2nd Year: Brachytherapy Flashcards
How does the AAPM recommend specifying source strength?
Air kerma strength
Why is Air Kerma Strength recommended over mg Ra Eq, activity, or exposure rate constant?
Air Kerma Strength can be esrtablished directly from primary standard measurements
The other terms cannot be
Why do we use Air Kerma Strength instead of dose rate in tissue for source strength specification?
Because air kerma strength is directly and absolutely measurable in a wide-angle free-air chamber
and
Because air kerma strength is already proportional to dose rate in tissue. So the conversion is easy enough
What kind of detector does NIST use to calibrate LDR lower energy sources (such as I-125 and Pd-103)?
Wide-angle free-air ionization chamber with 2pi area geometry
This chamber is large enough volume so electronic equilibrium can occur
What is the difference between a 2pi geometry and 4pi geometry chamber?
2pi geometry chambers are able to measure in a complete radian, 2D circle
4pi geometry detectors can measure in complete 3D sphere
2pi geometry detectors are inherently limited to a maximum possible efficiency of 50% (since they see only one side of a source)
What setup does NSIT use to calibrate LDR low energy soruces (I-125 and Pd-103)?
WAFAC to detect exposure rate
Filter wheel with various aluminum filters to absorb contaminant characteristic photons from titanium encapsulation of seeds
Seed rotated along longitudinal axis to average out axial non-uniformity
Source placed on nylon base to limit photon scatter by base
What correction factors does NIST include in their calibration of LDR low energy sources?
Temperature and pressure
Decay correction
Ion recombination
Photon attenuation in air
Filter and front electrode attenuations
Inverse-square
What is the traceability workflow for calibrating your well chamber for low-energy LDR sources?
NIST WAFAC –> ADCL transfer well chamber –> your well chamber
At each step, a calibration coefficient is created
As an alternative to calibrating well chamber for LDR low energy sources using traceability, what else can the ADCL do for your chamber?
Providing you with a standard, NIST traceable calibration source, so you can calibrate your well chamber manually
Which source is used for LDR low energy source calibrations at NIST?
Trick question. It is not one singular source. ADCL’s perform well chamber calibrations for specified seed types, not any one general isotope
In the past, it used to be only Cs-137. But the manufacturer builds of seeds have evolved throughout the years and they directly impact measurements, so each calibration is dependent upon the seed itself
True or False
As of yet, NIST has no standard for calibrating HDR sources, so instead ADCL’s perform a extrapolation based method published by Goetsch et al
False
It’s 90% correct. It should just read this instead…
As of yet, NIST has no standard for calibrating HDR sources, so instead ADCL’s perform a interpolation based method published by Goetsch et al
What transfer chambers does ADCL use for calibration of HDR sources?
Either a exradin A3 spherical ion chamber or a thimble chamber
Describe the general workflow that ADCL use to calibrate your well chamber for HDR sources
- Retrieve calibration factor for a transfer chamber (either spherical ion chamber or thimble chamber)
- The calibration factor is valid for Cs-137 (662 keV) and a medium-filtration x-ray beam (250 kVp)
- Interpolate to get a calibration factor for Ir-192 (energy between Cs-137 and medium-filtration beam)
- Calibrate activity using the “seven distance measurement technique”
- Once activity of the Ir-192 source is confirmed, use the source to derive a calibration factor for the well chamber at the sweet spot of the chamber
What is the purpose of the “seven distance measurement technique” used by ADCL to calibrate HDR source strength? How does it work?
Measure source from seven distances in air using the chamber and an equilvane tplastic buildup cap applying a distance correction at each position
Technique removes effects of room scatter from measurement
What are the units of air kerma strength?
uGy m2 / hr
What is the relationship between air kerma strength and air kerma rate?
Sk = air kerma rate * d2
What are we trying to find during a source calibration measurement?
Activity of the source
When performing a source calibration, where should you place your well chamber and why?
Center of room (or atleast 1 meter away from any wall or scattering material), on a plastic cart
To limit backscattering (affect can be as large as 1.1%)
Per TG 56, what two chambers are allowed to be used for seed assays?
Well-type chamber or farmer chamber in a jig 10 cm away from source
At what positions in the well chamber is the ADCL supplied calibration factor valid?
Sweet spot for HDR sources
or
Source holder holding position for LDR sources
True or False
For low energy LDR source calibration, the calibration factor must be obtained for specific models of the seed used
True
True or False
For high energy sources, such as Ir-192, calibration factor must be obtained for specific model of the seed used
False
You can use the calibration for whatever seed model, as long as it is the same isotope
True or False
For LDR well-type chamber calibrations, the source holder must be sent with the chamber?
True
What is the main difference between a pressurized and non-pressurized well-type chamber?
Pressurized chambers have greater signal, but must be checked for constancy to ensure that there has not been a leak
Non-pressurized chambers are open to air, so they must have a pressure correction component
In theory, where does the LDR seed holder place the source in the well chamber?
In an area of uniform response, which in theory would also be the sweet spot
What correction factors are used to convert well-type chamber current reading to air kerma strength?
Electrometer correction factor (from ADCL)
Chamber calibration factor (from ADCL)
Aion (correction factor from collection efficiency at time of calibration) (from ADCL)
Pion (collection efficiency at time of measurement) (we assume this equals 1.000)
Temperature and pressure
Label the following diagram…
True or False
For a well-type chamber, the pressure correction factor really only matters for low-energy photon emitting brachytherapy sources.
True
This is why for Ir-192 we dpn’t even consider the factor
Describe the rationale behind the pressure correction factor for a well-type chamber
Electrons produced by low energy photons have a range in air on the order of the collecting volume
As such, there will be an apparent over response if pressure increases
This is less apparent for higher energy photon or electron emitters because the electrons will have a large enough range to clear the volume regardless
What 4 quantities are multiplied together to give calibrated activity of a source?
A = I*Cal Factor*Unit Conversion factor*CTP
I is the raw current reading in amperes
Cal factor converts current reading to air kerma strength by applying electrometer correction factor, chamber calibration factor, and ion collection factors
Unit conversion factor is used to convert from air-kerma strength to acvtivity. This is typically 1 / the exposure rate constant multiplied by exposure rate conversion to air-kerma
CTP is temperature and pressure correction
What are the four reports that give recommendations for LDR source assays, and what years did they come out?
TG-40 (1994)
TG-56 (1997)
TG-64 (1999)
Low Energy Brachytherapy Source Calibration Working Group (LEBSC WG) (2008)
For individual seed batches, what is the recommended amount of sees that should be assay’d?
>= 10% of total seeds or 10 seeds, whichever is larger
For cartridge seed batches, what is the recommended amount of sees that should be assay’d?
>= 10% of total, either whole cartridge assay or individual sources
For stranded/cartidge sources, what is the recommended amount of strands that should be assay’d?
10% or 2 strands, whichever is larger
or
5% or 5 loose seeds from the same batch, whichever is larger
For stranded sterilized batches, what is the recommended amount that should be assay’d?
10% of total, whole cartridge assay in a sterile environment
or
5% or 5 loose seeds from the same batch, whichever is larger
Per the AAPM LEBSC WG, what is the recommended action levels for if the source strength assay at your site disagrees with manufacturer?
If calibrations…
Differ by < 3%, no action is required
Differs by 3-5%, an investigation is warranted
Differ by > 5%, need to consult the manufacturer
If clinic assay differs from manufacturer, which strengths do you use in the TPS?
If discrepancy is < 5%, use the manufacturer spec
If discrepancy is > 5%, use clinic assay result
True or False
If you don’t want to assay a stranded seed assembly, you can contract a third party serrvice to do it for you then they reassemble the seeds back into the customer order
True
The third party service will provide you with a assay report with information regarding the seed strength within the order
What are some QA we do for our HDR remote afterloader?
Source decay verification with an independent calculator
Interlock checks
Audiovisual checks
Radiation area alert monitors
PVT
Timer error test
Cateheter integrity checks
Presence of emergency tools
What HDR QA tests do we perform quarterly (source exchange)?
Everything we do for daily
+
Assay via well counter
PMI by service engineer
Backup power and battery checks
Dwell position offset check using film
Interruption timer check
Dwell time dosimetric effect (transit dose)
How often is a leak test required to be performed for eligible sources?
At the minimum once every 6 months
Have a general idea of the inside of the bravos afterloader
For HDR source activity calibrations, what is the tolerance for difference between your measured activity vs manufacturer calibration?
5%
Why is Ir-192 most commonly used for HDR and not another isotope?
HDR has a very high specific activity, so you can get a activity in a small volume
Then why don’t we use Co-60?
Because Ir-192 also has a lower photon energy than Co-60
What is the main purposes of HDR annual?
Inventory check of all devices and probes
Documentation of sterilization counts for all devices
Device constancy (no bends, breaks, objects or insects stuck inside anything, liquid, etc)
What do we do for HDR annual at our site that most sites do not do?
E2E testing
TPS model constancy check using gamma analysis
What are some advantages to HDR over LDR? (7 listed)
Increased dose optimization capabilities
Outpatient treatment
More stable positioning
Can add packing or other instruments to increase distance to normal tissues (since treatment times are shorter, this can work, just like packing for T&O)
Smaller applicators
Better documentation for treatment (HDR units have automatic documentation)
Reduction of exposure to workers
What are some disadvantages to HDR over LDR? (6 listed)
Increased potential for more serious errors
More technical difficulty
More complicated TPS
Less clinical history/research
Increased need for accuracy in dosimetry, geometry and anatomical information
Increased danger from exposure to workers in an emergency situation
What are the two types of errors in HDR? Give an example of each.
Systematic error - an error as a result of correctly following procedures, but with an inherent flaw in an assumption of either the dose calculation or deliver (Ex. incorrectly commisioned TPS)
Random errors - errors due to human error, lapse in judgment, device malfunctions
Which TG report gives recommendations for a well run HDR program?
TG 59
Per 10 CFR 35, what requirements make a medical physicists involved in HDR an authorized medical physicist?
Board certification
Atleast 2 years of full-time practical training and/or supervised experience in medical physics at a site that offers both EBRT and brachytherapy services
At a minimum, vendor-supplied training or authorized medical physicist trained for treatment unit and TPS
Written attestation from an AMP attesting to individual’s knowledge and skill for use of specified type of treatment unit
What material should an HDR treatment plan document include?
Indication of catheters used
Dwell positions, insertion lengths, and spacing between dwell positions
Isodose plots
Secondary calculations
QA check-off list
Any available post-treatment reports
What 3 important checks should be performed immediately after conclusion of HDR treatment?
Checking area monitor and GM meter to verify source is retracted
Verifying actual treatment time and positions agree with treatment plan values
Storing the room and HDR keys in a secure location
What are some important things to look at when reviewing a HDR treatment plan? (8 listed)
Verifying patient name and treatment date
Verifying decay of source strength
Verifying correct system files were exported to treatment unit
Verifying the use of any magnification factors
Verifying step size
Verifying prescription criteria are consistent with clinical intent
Verifying that dose per fraction matches prescription
Verifying dwell times and positions at treatment unit match those of the plan
What 5 key pieces of equipment are needed to be in proximity of patient in an emergency situation?
Forceps
Wire cutters
Lead pig
GM meter
Timer
Which isotope is used to treat thyroid cancer?
I-131
True or False
The vast majority of thyroid cancer is slow growing and curable?
True
The vast majority (97%) are either papillary (86%) or follicular (9%). Both are slow growing and curable
What fraction of thyroid cancers are aggressive?
1%
anaplastic
Where is the thyroid gland located?
Inferior to the laryngeal prominence (adam’s apple), anterior portion of the neck
How is I-131 administered?
Orally in the form of a liquid or pill
How many lobes is the liver separated into? How many segments?
2 lobes (right and left), 8 segments
Each segment is functionally independent with its own vascular inflow, outflow, and biliary drainage
True or False
Y-90 radioembolization for hepatocellular carcinoma is typically curative
False
HCC is typically discovered late, so Y-90 radioembolization is palliative
What two systems are used for Y90 radioembolization?
TheraSphere or SIR-Spheres
Both are microspheres injected by the physicists which work to limit radiation exposure. The difference is in their apparatus, microsphere construction and activity per sphere
What imaging is needed for Y90 radioembolization?
CT and MR contrast enhanced images so interventional radiologist can plan vascular access
Angiograms for vascular mapping
Hepatic perfusion study (gamma camera) to determine fraction of uptake to liver and lung (shunt fraction). If shunt fraction > 20%, treatment may be canceled
SPECT and/or CT to image after treatment to confirm uptake
CT, PET, or MRI no earlier than 3 months for follow up
What isotope is used in lutathera?
Lu-177
How does Lutathera selectively target tumor?
Attached to a dotatate (molecule that binds to GEP-NET cells that have a molecule called somatostatin receptor on surface)
What are the decay modes of Lu-177?
Primarily beta emitter
Secondarily gamma emitter
What is the FDA approved usage for Lutathera?
Certain cancerous neuroendocrine tumors affecting the digestive tract (Gastroenteropancreatic neuroendocrine tumors (GEP-NETs))
These are typically slow growing tumors
For a lutathera infusion, the prescribed infusion activity is 207 mCi/infusion. But the actual administered activity is 201-206 mCi typically. Why is this?
Some activity is left in the vial. Some has decayed before administration
How is a good candidate for Lutathera identified?
Take a PET scan using dotatte tagged with gallium-68 or a copper isotope to locate somatostatin receptor-positive tumors
This scan will show you upfront the uptake of the lutathera
A radiologist will sign off if they ar ea good candidate or not after discussion at tumor board
Blood lab tests are performed very frequently, with certain parameters constantly checked to ensure that nothing is out of tolerance. If anything is approaching tolerance, increase frequency of blood work
What is the method of administration for lutathera?
Intravenous (IV) infusion
What is another FDA approved theranostic nuclear medicine that uses Lu-177? What is it used for?
Pluvicto
Lu-177 tagged PSMA-617
Used for adult men with prostate-specific membrance antigen (PSMA)-positive metastatic castration-resistant prostate cancer (mCRPC) whose cancer has worsened despite receiving traditional therapies
What administration method is used for pluvicto?
Intravenous infusion
How often is Pluvicto administered?
6 separate infusions
6 weeks apart
No amino acid administration since load on kidney is less
Why is lutathera given with an amino acid solution before, during and after treatment?
To protect the kidneys by reducing how much radiation they absorb
Describe the workflow of lutathera administration from room prep to clean up
- Prep room and bathroom with throw away padding surrounding floor, couch, toilet
- Administer amino acid solution to patient
- Begin lutathera administration with a slow titration (100 mL/hr for first 15 mL, then if patient tolerating well increase to 300 mL/hr for 150 mL)
- during infusion continue amino acid administration
- After infusion, administer amino acids for additional 2 hours
- Patient urinates and voids prior to physicist
- Physicist takes measurement to determine if patient can be released
- Patient is released
- Nuc med techs use GM counter to find any potential lingering waste
- environmental services performs a clean up
What equation from which report was used to derive the 2.1 mR/hr for individual infusions, release criteria for Lutathera? Why did these equations need to be used? Give a general description of how the calculation is done.
Equations 2 from NRC 8.39
Had to derive the release criteria because the report does not have it pre-calculated
The value is derived based off 4 total infusions, and a maximum possible dose to any one individual calculation to keep that value below 5 mSv
The calculation first figures out the maximum allowed activity admiistered over the course of all 4 infusions, (310 mCi), which we well exceed, then calcualtes the corresponding dose rate at 1 meter for 310 mCi of Lu-177 (8.6 mR/hr), then divides by 4 for the dose rate per infusion (2.1 mR/hr)
What recommendations are given to Lutathera patients following release?
For the next 3 days
- Sleep in a separate bed and at least six feet away from anyone else
For the next 6 days
- Stay at least six feet away from children and pregnant women
- Menstruating women should use tampons that can be flushed down toilet
- Avoid using disposable items that cannot be flushed down toilet
- Sit while urinating and flush toilet three times with lid down
- Wash hands often, including after each toilet use
- Shower immediately after discharge from the facility and shower daily
- Drink plenty of liquids
- Use separate towels, washcloths, and toothbrush from rest of household members
- Do not share a toilet
For the next 6 months
- Do not become pregnant or breast feed
Additional
- Carry around a card to shown to officials anytime you may come in contact with a radiation scanner (such as at the airport)
True or False
For select liver tumors, Lutathera can be paired with bland embolization. Also what is bland embolization?
True
Bland embolization is the cutting off of blod supply to the tumor using alcohol. It does not add any additional radiation toxicity, so it can be paired with Lutathera.
How is uptake determined for Pluvicto patients prior to administration of drug?
Using a PET scan of PSMA tagged with a positron emitter
What fraction of men with prostate cancer are PSMA+?
> 80%
What is the active length of our bravos source?
What about varisource?
Bravos source: 3.5 mm active length
Varisource: 5 mm active length
What information is needed for commissioning of a brachytherapy TPS? (4 listed)
- Source dosimetry information (TG-43 data)
- Source geometry (length, weld tip, thickness, any other info), always put in by manufacturer at installation
- Dwell position specification
- Sk and activity for your source
When performing a source exchange, assuming you keep the same source model between commissioned source and new source, what is the only value that will change?
Sk will change because activity will be different
What are two methods during brachytherapy TPS validation that you can do to verify that the correct data tables have been entered into the source model?
- Make a simple plan and compare dose at a point to what is expected from the tables
- Go to data admin, look at the tables, and literally compare it directly to the TG report tables
What is the most likely thing that can go wrong during an LDR procedure?
Misplaced seed in the OR
What are the two most critical things that can go wrong during an LDR procedure?
(Hint: think dosimetric and geometric)
Seeds are never assayed and calibration was wrong
or
Physician placed seeds in the wrong location
True or False
LDR seeds, if not secured in placed, commonly start to move and occasionally can be transported elsewhere in the body
True
It’s pretty normal for seeds to move a bit, and it isn’t unheard for some seeds to be urinated or pooped out. In rate situations they may even travel to the rest of the body.
In general, if only a few seeds are misplaced, it does not make a huge dosimetric difference
If you were performing an IORT procedure, and the dose calculation software or computer crashed, and you couldn’t generate a plan, but the patient was on the table, what should you do?
Manually calculate the time needed to deliver dose by using PDD information
If, in IORT, the timer to stop the beam was malfunctioning, or the probe was not secured and fell out of the patient, what should you do and how?
Immediately stop the beam
Two methods to stop the beam…
- Press the abort button
- Unplug the power supply to the machine
For an HDR emergency, what is most likely to go wrong?
Source gets stuck inside of the patient
Either because it fell out from a kink in the needle, or the retraction mechanisms aren’t working
For an HDR emergency in which the source isn’t retracting, what is the general workflow that you need to follow?
- Hit the interrupt button
- Turn the key
- Hit the emergency stop button
- If nothing up until now has retracted the source, start a stop watch and enter the room
- Press the afterloader stop button. If this doesn’t retract source…
- Use the manual hand crank
- If none of the above has worked, physician intervention is needed to applications from patient
- Physician will throw application into emergency pig
- Wheel patient away from pig, and survey to ensure that no source is present in the patient
- If a source is still present, you need to quickly run the patient to the OR for surgical removal
- Once source is removed and in the pig, immediately move everyone from area and call radiation safety
- Use rules of thumb and stopwatch timer to estimate dose to workers
- Use TPS and delivered/stopped dwell times to estimate dose to patient
In the case of an HDR emergency in which workers need to enter the room, what TG report gives rules of thumb for estimating dose received?
AAPM TG-59
When receiving a new source, what 3 measurements of the container must you perform?
- Dose rate reading at surface of container
- Dose rate reading 1 meter from container
- Wipe test over 300 cm2 of surface
How often does the service engineer perform preventative maintenance inspection (PMI) on the afterloader?
Quarterly
(typically at time of source exchange)
What tests does the engineer run during a PMI?
Series of mechanical and sensing tests that ensure things like…
Wire speed, wire force, indexing, sensors, PVT, etc
Fun fact: many of these tests are performed with the machine open, inside of the room, MEANING, the source cable needs to be replaced by a dummy cable during PMI
In what clinical scenarios is IORT optimally used? (2 types)
- In scenarios in which a complete surgical resection will be difficult
Ex. Locally invasive tumor surrounding nerve or vessel that cannot be resected
Ex. Tumor invading bone that cannot be cut away
- For patients with prior EBRT in which normal tissue tolerances will be difficult to meet with more EBRT
What is the most common use of IORT in current day radiation oncology?
Accelerated partial breast irradiation (APBI)
What is this? What is it used for? What does it do?
Mobetron
A modality for intraoperative electron radiotherapy (IOERT)
Uses electrons up to 12 MeV to resection site
What are the two most commonly used IORT devices for breast IORT?
Zeiss Intrabeam and Xoft Axxent
Describe the general operation of a Zeiss intrabeam
Electron beam accelerated down 10 cm tube that strikes a 3.2 mm diameter gold target
This produces x-rays that emerge from a spherical plastic applicator available in sies 1.5 to 5 cm
6DoF positioning accommodated
Suture closes cavity around applicator, skin retracted
True or False
Xoft Axxent is a low kV IORT modality
False
Xoft Axxent is an electronic brachytherapy IORT modality
What is the only electronic brachytherapy modality that is commonly used for cervical cancer?
Xoft Axxent
Describe the general operation of the Xoft Axxent system
Electronic brachytherapy
Miniature x-ray tube (2.2 mm diameter, 10 mm length) in a water-cooled catheter
2.5 hr lifetime
Tube operates up to 50 kV and is heavily filtered, this provides radial dose function similar to low energy brachytherapy sources
If used for breast, a 3-6 cm balloon applicator is used to treat 1 - 2 cm depth either single dose, or fractionated treatments
What is a proposed use of Xoft Axxent that can come into use in the future if the source size can be reduced?
Interstitial brachytherapy
What is this and what is it used for?
HAM applicator
Surface applicator placed on placent with guide tubes that an HDR source can travel through.
Used for surface dose irradiation of certain surface level cancers
What is this?
Freiburg flap applicator
Besides breast, what are some other sites that may be treated using IORT? (list as many as you can, do not need to know all)
Colorectal
Pancreas
Gastric
Abdomen
Pelvis
Breast
gynecological
True or False
A 5 year study by TARGIT-A trial showed that 5-year local occurence rates between whole breast EBRT and IORT are similar
True
What three IOERT modalities are commercially available in the US, and which is the most commonly used?
Novac-7
LIAC
Mobetron (most commonly used)
In what scenario would internal shielding be needed in IORT for breast?
When tumor site is in close proximity to rib or chest wall
True or False
A freiburg flap applicator is a specific type of HAM surface applicator
True
What are the two major drawbacks to surface HDR?
- Since the source is not shielded on the side facing away from patient surface, you need heavy shielding for vaults. Additionally, the patient rest of body will also be given considerable dose
- Treatment times are relatively long (an excess of an hour in some cases)
Label the following diagram
True or False
There are currently no formal recommendations of the AAPM for dosimetry standards, formalisms, or adaptions of existing protocols for eBT
True
What are the two dose rate calculation datasets provided by Zeiss? Which is considered more accurate?
Calibration V4.0 (more accurate)
TARGIT (more commonly used)
What are the similarities between the two dose rate datasets used for IORT?
Both are a function of distance from the source
Both are measured by Zeiss
Both are measured in a water phantom
Both are measured in increments of 0.5 mm from depths 3 to 45 mm
What is the order of magnitude difference between the Calibration V4.0 and TARGIT datasets for Zeiss?
14% to 30% difference at surface of a spherical applicator
Difference depends on diameter
For Zeiss intrabeam, what for what applicator sphere sizes is the percent difference between the two available datasets larger?
Smaller or larger diameter ends?
Smaller
What is the procedure for Zeiss Intrabeam annual?
Send it back to the manufacturer
There it gets inspection, recertification, verification/updating of the dose rate data
Why do the TARGIT and the Calibration V4.0 datasets differ from one another? (two reasons)
- Because they used two different chambers to measure the dose distribution
The V4.0 uses a 0.005 cc parallel-plate chamber
TARGIT uses a 0.02 cc parallel plate chamber
- The TARGIT trial measures exposure then converts using 0.881 cGy/R (this is not specific to the photon energy spectrum of the INTRABEAM however, and so is not entirely accurate). The Calibration V4.0 has absorbed dose in water calibrations for different peak voltages
Describe the TARGIT-A clinical trial
This was a clinical trial that began in 1998 in which 2000 patients were treated
As part of the trial, a formalism was created and given to all participating sites so every single site would be using the exact same dose rate at applicator surface (20 Gy at surface regardless of applicator size or any new protocol)
True or False
For the Zeiss Intrabeam, you can switch between which protocols you want to use (TARGIT or Calibration V4.0)
This is partially true, partially false
One system allows you to (INTRABEAM 600)
One system forces you to use TARGIT (INTRABEAM PRS500)
Per TG-292, For spherical applicators, which protocol should you use?
TARGIT or Calibration V4.0?
If you have INTRABEAM 600 you can use either option since both are available
If you don’t have the choice, then of course you must use TARGIT
Per TG-292, for Zeiss INTRABEAM IORT, which protocol should you use for needle, surface and flat applicators?
TARGIT or Calibration V4.0?
Calibration V4.0 if available
True or False
If your clinic follows the TARGIT trial, you MUST use the TARGIT dataset provided by Zeiss for Intrabeam IORT
True
What QA tests are performed on the Zeiss IORT INTRABEAM system prior to every patient?
Probe adjuster check (rotating the probe to make sure it still stays center in holder)
Dynamic offsets (using photodiode to determine position of photons coming out of the accelerator)
PDA source check
PAICH (output check with spatially designed parallel-plate type chamber)
ERM check (dose rate check)
What safety redundancy does Zeiss INTRABEAM employ to ensure that the radiation does not stay on longer than it should?
It was a two check system
The first shield is the internal radiation monitor which stops treatment after prescription is given
The second shield is the timer, which stops treatment if the time exceeds 10% of what was expected
What kind of surgical procedure does breast IORT occur during?
Lumpectomy
In the case of a interstitial prostate emergency in which the usual steps from outside of the treatment room (retraction of source), and retraction of source from inside of the vault do not work, what is the following procedure and who performs it?
(keep it to small detail, 1 sentence answer)
Hold grid in place, grab all needles, and pull
Physician performs
In the case of a endobronchial emergency in which the usual steps from outside of the treatment room (retraction of source), and retraction of source from inside of the vault do not work, what is the following procedure and who performs it?
(keep it to small detail, 1 sentence answer)
Pull out catheter and dump in pig. Connect two translucent rubes to resume oxygen supply to patient
Physicist performs
In the case of a capri applicator usage emergency in which the usual steps from outside of the treatment room (retraction of source), and retraction of source from inside of the vault do not work, what is the following procedure and who performs it?
(keep it to small detail, 1 sentence answer)
Connect syring and deflate balloon and pull from patient
Physician performs
In the case of a T&O with gauze packing emergency in which the usual steps from outside of the treatment room (retraction of source), and retraction of source from inside of the vault do not work, what is the following procedure and who performs it?
(keep it to small detail, 1 sentence answer)
Remove gauze, loosen locking nuts, spread ovoids apart, remove only the offending applicator and keep removing applicators if the dose remains high
Physician performs
In the case of a T&O with balloon packing emergency in which the usual steps from outside of the treatment room (retraction of source), and retraction of source from inside of the vault do not work, what is the following procedure and who performs it?
(keep it to small detail, 1 sentence answer)
Deflate balloons and withdraw them both, loosen locking nuts, spread ovoids apart, retract offending applicator, and keep removing applicators if radiation is still high
Physician performs
In the case of a SAVI emergency in which the usual steps from outside of the treatment room (retraction of source), and retraction of source from inside of the vault do not work, what is the following procedure and who performs it?
(keep it to small detail, 1 sentence answer)
Engage locking mechanism, collapse device, and withdraw from patient
Physician performs
In the case of a mammosite/contura emergency in which the usual steps from outside of the treatment room (retraction of source), and retraction of source from inside of the vault do not work, what is the following procedure and who performs it?
(keep it to small detail, 1 sentence answer)
Connect syring to INF, collapse device and withdraw from patient
Physician performs
In the case of a AccuBoost emergency in which the usual steps from outside of the treatment room (retraction of source), and retraction of source from inside of the vault do not work, what is the following procedure and who performs it?
(keep it to small detail, 1 sentence answer)
Disengage chair brake, pull emergency lever to release compression paddle, wheel patient towards maze
Physicist performs
In the case of a single channel stump emergency in which the usual steps from outside of the treatment room (retraction of source), and retraction of source from inside of the vault do not work, what is the following procedure and who performs it?
(keep it to small detail, 1 sentence answer)
Loosen stump nut and remove flexible probe, place probe into pig
Physicist performs
In the case of a T&O with gauze packing emergency in which the usual steps from outside of the treatment room (retraction of source), and retraction of source from inside of the vault do not work, what is the following procedure?
(keep it to small detail, 1 sentence answer)
Release centering mechanism and withdraw catheter from patient
In the the case of exposure to unshielded HDR source, approximately how long will it take for the whole body limit to be reached for a radiation worker (1 cm and 10 cm from source)
1 cm: ~ ½ second
10 cm: ~ 40 seconds
True or False
For an endobronch procedure, an anasthesia tech (CRNA) will be present and will be in charge of resuscitating patient in an absolute worst case scenario
True
Why was pulsed dose rate brachytherapy (PDR) historically developed?
In the beginning, only LDR data existed, but HDR was starting to become more frequently used. So PDR was used as a transitional delivery method while the change was being made from LDR to HDR
What is the difference between PDR and HDR?
They’re essentially the exact same thing, but PDR delivers fractions of the total dose at preset times
Both use an afterloader and the same sources
What four systems are used for surface brachytherapy?
(1 is HDR and 3 are electron brachytherapy)
HDR with Ir-192 or Co-60
Axxent
Zeiss INTRABEAM
Esteya (Elekta)
Which manufacturer produced HAM flaps for surface brachytherapy?
E&Z BEBIG (formerly Mick)
Per TG-253 what is the recommended dose calculation protocol to use for surface brachytherapy applications?
There is no one recommendation. But…
For materials and applicators that are water equivalent, TG-43 is acceptable
For molds/flabs that aren’t water equivalent, a TG-43 hybrid is recommended
For cone applicators or other shapes that aren’t water equivalent such as Axxent or Intrabeam, use published dose distribution measurements
If model based dose calculation algorithms are available at the clinic, consider using them
What three limitations are inherent to TG-43?
- Does not account for heterogeneities in patient or applicator
- Does not account for interseed attenuation
- Does not account for patient dimensional boundaries
What are 4 classes of brachytherapy algorithms beyond TG-43?
- 1D ray tracing - this ultimately failed to account for secondary scatter and is no longer used
- Collapsed Cone Convolution/Superposition (Elekta) - Ray tracing used to scale primary fluence and primary scatter but multiple scattering is not accounted for
- Grid Based Boltzmann-Equation Solvers (Like Acuros) - attempts to solve boltzmann equation by discretizing spatial, angular and energy
- Monte Carlo - solves boltzmann equation through random sampling
What is the difference between reporting DM,M vs DW,M? Which does TG-186 recommend you using?
The first term is dose to medium calculated in a medium
The second term is dose to water calculated in a medium
TG-186 recommends dose to medium in medium
The 2nd term needs a conversion of dose to medium to water, and is often considered less accurate due to the conversion step. For EBRT this discrepancy can be up to 2%, but for low energy sources, this discrepancy can be up to 80-90%
True or False
For model-based brachytherapy algorithms, soft tissue is essentially water equivalent
False
Because of the lower energies in brachytherapy, there is more significant difference between soft tissue and water than there is in EBRT
True or False
Mass density is dircty proportional to electron density
True
What data is needed for a model-based brachytherapy algorithm?
CT voxel by voxel material determination in order to figure out…
Atomic number
Cross section vs energy
Effecive atomic number as a function of energy
What is the major lf assigning tissue types in model based brachytherapy algorithms?
Within the soft tissue range, -100 to 100 HU, for low energy sources, it is very difficult and somewhat a guessing game to determine exactly which tissue type and corresponding medium information
How do you validate a model based dose calculation algorithm in a homogenous medium? What about heterogenous?
Homogenous - compare against TG-43 protocol calculation in water phantom for a single dwell position. 2% tolerance or gamma analysis of 2%/2mm with pass rate > 99%
Heterogenous - compare against MC calculated dose that has been calc’d in a heterogenous phantom. 2%/2 mm with pass rate > 99%
Fill in the blanks regarding MC, Collapsed Cone, and Acuros for brachytherapy calculations
As distance from source increases, dosimetric uncertainty _______
As CT voxel size decreases, dosimetric uncertainty _______
As distance from source increases, dosimetric uncertainty increases
As CT voxel size decreases, dosimetric uncertainty increases
True or False
Due to the difference in calculated dose using more accurate models vs the TG 43 historically prescribed doses, TG 186 recommends sticking to the TG 43 protocol for dose calculations until more research is available.
True
If all empiracle data is based off TG-43, then TG-43 should be used
Which isotope has been historically most commonly used for prostate LDR?
I-125
Which isotope is starting to gain popularity for prostate LDR and why?
Pd-103
Data is starting to show slightly increased control while reducing side effects
For patients with a high gleason score, would you use longer or shorter half-life isotopes for LDR prostate seed implants?
Shorter half-life
A high gleason score means the cancer is more aggrssive, so you would want to give dose as quickly as possible
What is the title of TG 56? What does it go over?
Code of practice for brachytherapy physics
Goes through recommendations of what makes a good brachytherapy program. This includes documentation, workflow, recommended quality checks, etc
True or False
Activity needs to be specified in the TPS for each source
False
Almost true… you don’t actually know the activity of a source, you only know the apparent activity. So apparent activity must be specified in the TPS for each source
What does a nomograph show?
Total seed strength required to deliver given dose to a tumor of measured dimensions
Independent variable: size of target volume
Dependent variable: Total cumulative dose or strength utilized
True or False
Nomographs were originally designed to plot target volume vs number of seeds needed for LDR, but can be used to plot target volume vs Curie*Seconds instead
True
Prior to computer planning for seed/source locations, what systems were used to define interstitial implant orientations?
Manchester system (peripheral sources define target region, and you want max uniformity)
Quimby system (equally spaced, uniform strength sources distributed over source plane) (never picked up, but it’s uniform source placement rule is still widely used)
Paris System - parallel, uniformly spread source lines of equal strength and length. Yields significant normal tissue within treatment isodose line
What are some examples of LDR seeds (non-prostate) procedures?
T&O
Eye plaques
Californium-252 for advanced GYN tumors
Permanent Mesh Lung Implants
Intravascular brachytherapy
What type of radiation does Californium-252 emit? Why is this important?
Emits gamma and neutrons
Neutrons have high RBE and low OER. THis is great for hypoxic tumor cores as you’d see in advanced GYN tumors
Since dose fall-off is drastic as well, the neutrons wouldn’t be a big concern for the rest of the body
This was the original rationale of the treatment, but is no longer used
True of False
Intravascular brachytherapy can be either LDR or HDR?
True
Which isotopes would be used for intravascular LDR with mesh stents?
P-32 or Y-90 (both beta emitters)
When is intravascular brachytherapy used?
Following angioplasty or stenting of a blocked artery
This is to avoid restenosis and recurrent arterial blockage due to scarring for blockages resistant to drug infuse stents or anti-coagulant drugs
Why is intravascular brachytherapy LDR no longer used?
Due to “candy wrapper effect”
That is, restenosis forming at the end of the LDR stent
So now HDR is exclusively done for these procedures
What sources are most commonly used in eye plaques?
I-125 or Pd-103
What does COMS stand for and what is it?
Collaborative Ocular Melanoma Study
Study which standardized treatment for brachytherapy patients (including prescription and plaques to use)
What is eye plaque LDR used to treat?
Ocular Melanoma
What are two alternative treatments to eye plaque LDR?
Proton beam therapy and enucleation (removal of eye)
What are the available diameters for COMS eye plaques?
10 mm to 22 mm diameters with 2 mm increments
What is the general rule of thumb for deciding which diameter eye plaque to use?
Largest diameter of tumor + 2 mm margin
Ex. if tumor max dimension is 14 mm, you want 14 + 2 + 2 = 18 mm plaque
If odd number, round up
True or False
COMS has defined the plaques, prescription, calculation methods and reporting criteria for I-125 and Pd-103 treatments
False
Only I-125
What is the name of the ophthalmologist provided illustration that shows a projection in a coronal view of the white of the eye and is used to localize the lesion in eye plaques?
Fundus Diagram
True or False
For right eyes, the optic nerve enters the eye from the right side, and vice versa for left
False
For right eyes, the optic nerve enters the eye from the left side, and vice versa for left
What two localization techniques can be used for eye plaques to localize the tumor during treatment?
Ultrasound or transillumination
What is the purpose of the dummy plaque in an eye plaque surgical procedure?
Placeholder for ophthalmologist to begin suture placement around localized/marked lesion
Will be replaced with the actual plaque during the surgical procedure
How is a fundus diagram produced?
Tumor is localized using fundoscopy, ultrasound, CT or MRI
From there an ophthalmologist will make the fundus diagram
Which AAPM report gives reference tables for dose calculations for eye plaques central axis and radial doses for homo and hetero and is essentially just an improved TG-43 specifically for eye plaques?
TG-129
What is the eye plaque made out of?
Gold alloy
i.e, it’s expensive. So they are constantly sterilized and re-used
And silastic insert that contains the seeds
What plan documentation was needed from our site for LDR seeds when we had the program?
- Written directive
- Treatment plan report and isodoses (from variseed)
- Needle pre-plan configuration (example shown below)
- Theragenics order form (seed needle configurations for stranded seeds, if stranded were used, otherwise pre-loading instructions)
- Seed order confirmation
- LDR seed calibration spreadsheet
- Physics consult
- Post-plan (variseed)
What information goes into a seed order form for LDR?
- Stranded vs unstranded
- Sterile vs non-sterile
- Number of seeds needed
- Sleeves needed depending on applicator used
- Assay services
- Isotope
- Activity per seed
At our site, for LDR prostate, what isotope did we use?
I-125
Per Tg-64, how soon after LDR prostate implant should you follow up post-plans for I-125 and Pd-103?
I-125: after 4 weeks
Pd-103: after 2-3 weeks
What is the general LDR prostate workflow?
Volume study
Pre-plan
Seed order
Receiving seeds
Seed calibration
Implant
Post plan
What is the general procedure of a LDR prostate seed post plan?
Acquire a volume study
Ask physician to contour prostate, or do it yourself with other imaging guidance if they’re not available
Count total number of seeds and compare with what was originally implanted
Identify seeds and assign prescribed activity
Calculate dose distribution and compare to original plan (this can be done with comparing dose to a point in radcalc)
What makes a person a good candidate for prostate seed LDR alone vs prostate seed + EBRT?
Monotherapy: Patient has lower risk disease, good life expectancy, acceptable urinary function and favorable anatomy
LDR+EBRT: Select patients with intermediate or high risk disease
What are some commonly used isotopes for prostate seed LDR? What is THE most commonly used?
I-125 is THE most commonly used
Others include Pd-103, Cs-131, Au-198
What is the encapsulating material of prostate seeds typically?
Titanium
In addition to a titanium encapsulation, most seeds also have high electron density material embedded in them. Why? What are some examples of ones that are used?
To improve visibility on x-ray images
Commonly are lead, silver, gold, or tungsten
For on the spot planning, what kind of seeds would most definitely be used? Loose of stranded?
Loose
You don’t know the distribution you want ahead of time so you can’t pre-plan a strand
What are two major benefits to using stranded seeds over loose seeds in LDR procedures?
Seeds are less likely to migrate
Less radiation exposure to staff
What is the major benefit to using loose seeds over stranded in LDR?
Better control of distribution optimization on the spot
In general, as half-life of a LDR prostate seed decreases, the prescribe dose __________
In general, as half-life of a LDR prostate seed increases, the prescribe dose decreases
Since you’re giving dose over a shorter time, you need to give less dose in order to give the same biological effect as a longer half-life isotope with higher dose over longer time
In an LDR prostate written directive, there is typically two sections, one for before implanting and one for after. Why?
Because edits may be made to strategy due to unforeseen medical circumstances arising during the implant procedure
In a typical clinic, when is the pre-implant planning performed?
Several days to weeks before the implant
For pre-planning prostate seed LDR, what is the earliest you are allowed to take a imaging study for pre-planning?
2-3 weeks
Any earlier than that and the prostate may change significantly
What is the most accurate pre-planning image modality that we can use?
Trans-rectal ultrasound
This is because it A) gives a nice visualization of the prostate, bladder and urethra, and B) is the exact setup that will be used when implanting the seeds
Terminology:
The base of the prostate refers to the most ______ portion of the gland, and the apex refers to the most _______ portion
The base of the prostate refers to the most superior portion of the gland, and the apex refers to the most inferior portion
How is a nomogram used in LDR prostate seeds?
Once the volume of the target is measured, the nomogram is used to predict how many seeds would need to be ordered
This holds true for both pre-planning and live-planning
What anatomical structure is the limiting factor for whether or not a LDR prostate seed procedure (or even HDR) can be performed?
Why is it so important?
The Pubic Arch
You need to be able to access the entire prostate, and you can’t send needles through bone
For patients with a narrow pubic arch and a relatively large prostate gland, what portion of the gland will be difficult to access with needles?
Anterior-lateral sectors
How are the urethra and bladder visualized during LDR and HDR prostate procedures?
Foley catheter
What is the major benefit to live-planning vs pre-planning? What is the major downside?
Live-planning allows you to plan in the exact setup that the patient is in during the implants
Live-planning is also more difficult and faster paced since you need to do more inside of the OR. There is more possibility of error. And it also increases staff dose since you’re in proximity to sources for a longer time since pre-loading is not possible without a pre-plan
For all brachytherapy procedures, when should you survey the patient?
Before the procedure to get a baseline
After the procedure to either ensure no radiation present (HDR), or to see if release is possible (LDR)
What are the two major sources of error in LDR which are the reason why we have to post-plan?
Seed migration (can be limited using stranded seeds)
Edema (which increases volume of prostate by 40-50% soon after procedure)
What is the some purposes of post-implant dosimetry?
Ensure quality of implant and dosimetric coverage
Provide ongoing quality control metrics
Verify seed count
Give clinician opportunity to anticipate potential complications or to implant additional seeds or supplement with EBRT
What is the most practical time to perform a post-plan for LDR prostate seeds?
Immediately after or within 24 hours
It allows you to make any corrections on the spot as soon as possible
However this will cause coverage to be underestimated by about 10% since prostate volume will seemingly increase
According to the ABS, what is the most common LDR prostate seed post-plan timeline?
After 30 days
73% of clinics use this according to ABS survey in 2010
In the old days, x-rays were used to check for seed migratio in lung or brain. Why is this no longer recommended?
- It was rare
- New tech and manufacturing makes it even less likely
- X-ray generated unecessary dose to brain or lung
- Even if it was discovered, a procedure to remove the seed is more dangerous than keeping the seed there itself
True or False
The most commonly used post-plan imaging modality is MRI?
False
Due to the seeds having no signal in MRI, it’s not practical to use. Instead CT is the most commonly used (and in some isntances CT + MRI may be used to contour the prostate)
What equation is used to estimate LDR seed implant dose? (the general equation)
D = initial dose rate * 1.443 * T½
or
D = initial dose rate * mean time
In our clinic, what are the four major categories on our written directive form?
- Preliminary written directive (dose, isotope, signature, date of signature)
- Final written directive (activity per source, total activity implanted, prescribed dose, consult requested or not, signature, date of signature)
- Room survey (performed by, date, meter model and SN, reading, trash reading, linen reading, OR table reading)
- Seed inventory data (seeds ordered, seeds implanted, leftover seeds, who performed inventory, activity per seed)
In the LDR seed inventory form, what is some important information to list?
seeds ordered,
Patient names,
prescription,
remaining seeds,
total initial measured activity of remaining seeds and all other preceeding checking dates,
Date of disposal
Exposure reading at disposal
Method of exposure
Time in storage (10 half-lives)
For essentially all seed implant systems, what are the two major dose distribution design goals?
Uniformity within target volume
Sharp dose gradient outside of target volume
Fill in the blank
Per the Paterson-Parker planar implant rules, the larger the cross sectional area of a target is, the _________ the contribution of activity from the periphery will be
Per the Paterson-Parker implant rules, the larger the cross sectional area of a target is, the smaller the contribution of activity from the periphery will be
In the Paterson-Parker Planar and Volume implant systems, what is the approximate needle spacing?
< 1 cm
What are interstitial needles commonly made of? What is the material that we use in our clinic?
We use plastic. But they can also be made of…
Titanium
Surgical steel
What is a pro and a con to using surgical steel interstitial needles?
Pro: It’s the most durable of the available material
Con: It produces the worst CT artifacts of the available material
Up to what magnetic field strength is titanium MR safe?
3T
The implication of this being that for most clinical MRI’s, titanium will be MR safe
When would interstitial needles ever be used for gynecological applications?
When EBRT fails to shrink the tumor size efficiently enough such that intracavitary implants alone are able to get satisfactor coverage
Intersitital needles, typically two or three, would be used along side the T&O or T&R implants for bulky disease to help improve coverage
In what situations would HDR not be a viable mono treatment modality?
When the HDR by itself is not enough to target the entire spread of disease
Ex is in prostate + EBRT, where the EBRT is needed if there is disease spread to local lymph nodes. The HDR will not be able to reach the nodes
In addition to prostate, what are some other sites in which intersitial can and has been used for LDR or HDR?
Breast
Base of tongue
H&N
Sarcomas
Lung cancers
These have all been largely phased out by IMRT, but in rare situations you may see them
If any seeds were accidentally placed in the bladder or urethra, what is the procedure that can be used at the end of the implant procedure to remove those seeds?
Cystroscopy
(endoscopy through the urethra up to the bladder to check for any loose seeds)
What is the region of muscle in which intersitial needles are inserted through to access the prostate?
Perineum
area between anus and scrotum
The exact muscle is the perineal body
What is the first and most important step in creating a workflow for a new brachytherapy procedure?
Determining who is responsible for what
What is everyone’s role in the team?
Are our prostate templates (“Best Medical”) MRI safe?
NO!
What equipment is needed throughout the course of a HDR prostate procedure? (include the manufacturer names)
- “Best Medical” Prostate template
- 15G “Best Medical” Plastic Flexible Needles
- “Best Medical” Steel stylets (the thin steel needles that you put through the plastic needle to help push)
- Civco stepper/stabilizer
- BK Ultrasound and rectal probe
- “RPD Inc” Slessinger Board
- Transfer guide tubes
- Survey meter
What is this? Is it MRI safe?
Slessinger board
Yes, it is MRI safe
For a prostate patient, what is the general patient transfer workflow? (where do they start, where do they finish)?
- OR
- Recovery room
- CT Sim
- HDR Vault
- Urology
- Recovery
When inspecting a prostate needle placement, what are some things you should check for?
Do needles reach the bladder/prostate interface? (if not, push is necessary)
When inspecting a prostate needle placement, what are some things you should check for?
Do needles reach the bladder/prostate interface? (if not, push is necessary)
Needles that penetrate critical structures
Bladder is full and catheter is clamped
Prior to using the bravos for checking obstructions/length of channels, what would the physicists have to do instead?
Run the “pokey stick” through every needle to make sure that the lengths are consistent and there are no obstructions/broken tips
What is the purpose of marking needles/applicators in brachytherapy CT sim?
To ensure that nothing slipped in the time between CT sim and delivery of radiation
Marking should be performed immediately after an acceptable CT is taken
Run through the entirety of the HDR prostate treatment planning and delivery workflow outloud from the moment the patient arrives to CT sim to the moment the needles are pulled
- Patient arrives at CT sim
- CT is taken
- If needles need to be pushed, they are pushed and CT is retaken
- Once acceptable scan is taken, needles are marked
- Alcohol pads are used to remove any blood outside of needles
- Visual inspection is performed to ensure nothing is inside of the needles
- Patient is transferred onto mobile bed
- Patient transferred to HDR vault
- Treatment planning begins
- Once the needles have been numbered on the grid, one physicist (resident) goes in and marks with colors
- AMP double checks color marks
- Resident hooks up TGTs to afterloader
- Resident hooks up TGTs to needles
- Treatment plan is completed
- AU planning approves
- AMP performs checks
- AMP treatment approves and exports to treatment delivery system
- (in the case of Bravos, path lengths and obstructions are checked by afterloader), otherwise physicist runs wire manually through all channels (this would’ve been done before step 13)
- Final treatment time-out is performed with everyone present, ensure emergency pig is by afterloader
- Deliver treatment
- Physicist unhooks TGTs from needles
- Nurse removes sutures
- Physician removes needles and template
True or False
It is difficult to distinguish SpaceOAR from rectum muscles in a CT?
True
When reviewing a HDR plan after before treatment approval, what are some things you would check?
Correct patient
Correct fraction number
Correct dose/Fx
Correct activity of the day
Total curie-seconds agrees with any previous treatments (or with nomogram)
Total treatment time on console = treatment plan
No obstructions in needles and lengths make sure
Correct channel needles are identified on plan vs in real life
No dwell times < 0.4 seconds
Secondary dose check is within tolerance
While checking the HDR prostate needles marks before hooking up the TGTs, you notice that one of the needles black mark is not on the grid.
Before pushing needle, what can you check first to make sure that a push is actually necessary, and that the mark was not poorly made?
Check the longitudinal difference between that needle and a correctly marked needle
Go to CT, double check the longitudinal difference between the same two needle ends on that as well
If they agree with one another, then a push was not necessary and the marks were just poorly made
Alternatively, you can check the longitudinal location of the two needle tips, and the difference should also be the distance between the connection ends (since all needles are the same length)
In our clinic, what is the channel selection criteria for T&O patients?
Channel 1 is tandem
Channel 2 is pt right ovoid
Channel 3 is pt left ovoid
What is seroma?
Build-up of clear fluid inside of the body
Most commonly occurs after surgery
For APBI treatments, what are the critical structures of concern?
Chest wall, rib, skin, lung
In APBI with balloon catheter, how is the target volume defined? How is PTV eval defined?
1 cm annulus around balloon, subtracting out balloon and air/seroma
And subtracting any PTV that extends closer than 5 mm to skin surface
And subtracting any PTV that extends into ribs or pectoralis muscles
For PTV_Eval, subtract the balloon from the PTV
What are the three major types of breast brachytherapy?
- Interstitial
- Partial breast using applicators implanted in surgical cavity
- IORT
For HDR APBI, what are the two most commonly used applicators?
MammoSite (intracavitary balloon)
Savi (strut adjusted implant)
What is the main limiting critical structure in APBI HDR?
Skin dose, specifically 5 mm thickness to skin surface
Which calc algorithm is used for MammoSite?
TG-43
Briefly describe the design of a MammoSite applicator
Device that fills a sphere with a saline solution. A silicone catheter is located in the cetner of the balloon (can be one applicator, or often more)
Balloons are available in a number of sizes and will mold to the lumpectomy cavity tissue into a spherical shape
How long after implanting of the MammoSite is it recommended to wait before imaging for treatment planning? Why?
A few days
This will allow time for air pockets to resolve and seroma to drain
Remember: you need air/seroma surrounding applicator to be < 10% of the PTV_Eval
By surrounding applicator: this means within 1 cm of applicator
What MammoSite devices did we use in our clinic? Briefly describe it
Contura (shown below)
It was a 5 channel applicator that allowed for some some additional dose optimization, oriented in a cross or X depending on orientation
Additionally, we also had MammositeML which was smaller and 4 channel oriented in a Y
What is the limiting factor for MammoSite single channel applicator usage? How does a multi-channel applicator help work around this?
Proximity of lumpectomy cavity to skin
Need at least 7 mm spacing to avoid late-term toxicity with unsatisfactory cosmesis outcome
Multi-channel applicators allow for better dose shaping, thus allowing work-around from this limit
Describe the general design of the SAVI applicator for breast?
SAVI stands for Strut Adjusted Volume Implant
It’s a multi channel catheter that is shape conforming to fill the cavity
What is this?
Intersitial needle template grid for breast HDR
When would interstitial breast HDR be used over the other applicators?
Non-resected or irregularly shaped volumes
For interstitial breast HDR, what is the optimal way to orient the needles in order to minimize dose to contralateral breast and minimuze patient exposure?
Needle tips oriented towards midline
(Recall, radiation is strongest radially)
What modality is shown here? Very briefly describe it.
AccuBoost
Think mammogram, but with a brachytherapy applicator attached to a holding with openings in them. Afterloader delivers the radiation.
Breast compression to stabilize and remove overlapping tissue surrounding tumor
Image guidance with mammogram
Which applicator has better dose modulation capabilities, SAVI or Contura? Which is easier to implant?
SAVI has better modulation
Contura is easier to implant
For APBI CT sim, why do we ask patient to perform a small breath hold?
To reduce motion artifacts and make catheter tracing easier
What markings are done for APBI using Mammosite/Contura?
- Marking on skin where applicator meets skin. Mark both applicator and skin
This is to check for rotation of applicator (remember it’s spherically symmetric, but the dose distribution isn’t, so you need to be extra careful to make sure that it didn’t rotate)
- Marking to denote skin insertion depth to make sure it isn’t slipping out fraction to fraction
What type of TGTs does Contura/Mammosite use?
Collet style
In tracing channels for Mammosite, the highest number channel always corresponds to the center channel. The other channels are numbered starting by identifying Channel 1, then labeling CW
Due to the symmetry of the applicator and the possibility for rotation, what is an easier and safer way to distinguish the outer channels on a CT?
Run different style radio-opaque wires through one of the channels, this should give you a reference point of your “channel 1”
From there you can number them CW
For APBI, how often should you CT?
For cases in which site is near critical structure, and a small change in anatomy can bring dose into critical structure, you should Re-CT for all AM fractions and double check distance and air/seroma (suck any out if needed)
If re-plan is necesary, it should be done
PM-fractions are typically scout only
For APBI, how often should you perform scout imaging?
Before every fraction
For Mammosite, this is to check the volume of the balloon to make sure nothing changed and rotation
For SAVI, this is to check expansion/size against the reference scout and rotation
How is patient reproducibly setup for APBI in our clinic?
Vaclok
Arms down for comfort
How is the MammoSite balloon filled/deflated?
There is a port that directly accesses the balloon for that exact purpose
What is the main safety concern with PDR vs HDR?
In PDR you are moving to source more times than in HDR and in an uncontrolled/unspecialized holding area
Not only is there a higher probability of machine error, but the staff in vacinity is also not specialized in radiation therapy
What markings are necessary to make on the SAVI setup?
To check for rotation, make mark on applicator and on skin. Marks should align
Distance of skin to hub
For SAVI, what kind of TGT is needed?
Collet Style
For SAVI, what do you need to account for around the applicator?
Air
Seroma is not as much of an issue for SAVI procedures
For SAVI procedures, what is the maximum limit of air that is allowed to surround the SAVI?
Maximum volume of air < 10% PTV eval
How many channels does SAVI have? How are they oriented?
7, 9 or 11
Channel 1 in the center, surrounded by the other channels in a circular formal
How is the size of SAVI usage decided?
Based off of the measurement of te cavity along the long axis and the daiameter of the cavity under ultrasound
True or False
Before every Accuboost procedure, you should review the emegrency procedures with the patient
True
Essentially the procedure is that, in an emergency situation, the patient is asked to stay seated and do not stand up or aid
Describe the general workflow of a Accuboost treatment delivery?
Patient set up with compression paddle
Mammogram to align (IGRT) (using surgical clips in lumpectomy site)
From the mamogram, the rad onc decides the position and type and shape of applicator
Consult nomogram to calculate dwell time for each opposed pair for the specific applicator. NOTE: NOMOGRAM CALC IS APPLICATOR SPECIFIC
Applicator (using grid that follows mammogram) is then snapped into place (see image below)
Attach catheter of source holder to TGT, then afterloader, HDR
Deliver at dwell locations specified by nomogram
Remove then snap applicator to opposing location
Copy and paste the plan and deliver on the opposite side
Repeat the entire process again but for the two orthogonal opposed fields (if APBI) or the one orthogonal field (if boost)
Note: For each pair of opposing fields, a mammogram, the location/size/applicator is decided, and dwell time calculations are done with the nomogram for each step of the process. So that is 2 mammograms
Note: For Accuboost, there is no CT sim. All treatment planning is done using mammogram. And all planning is done on the spot. Total treatment is about 20 mins per fraction
What is the main benefit of Accuboost over EBRT for boost treatment (non-monotherapy)
AccuBoost is able to get a much tighter dose distribution and it uses on the spot mammogram image guidance daily
What are the three most common HDR afterloaders? Which do we currently have, which did we use to have?
GammaMedPlus iX
Varisource iX (used to have)
Bravos (currently have)
What information input does the nomogram for AccuBoost require for dwell time calculations?
Applicator type and size
Planned activity from first fraction (the times will get scaled for subsequent fractions on the machine console itself)
Plate separation Separation (thickness of breast)
Percent isodose line
Prescription (Note: if you have 2 sets of opposed fields, divide prescription by two and make two different nomograms for the two different pairs)
How many nomograms are made per AccuBoost fraction?
If it’s only 1 pair of opposed fields, then 1 nomogram
If it’s 2 pairs of opposed fields, then 2 nomograms
Essentially, 1 nomogram per opposed pair per fraction
What dose calc algorithm is used for Endobronch at our site?
TG-43
What is the limiting normal tissue in Endobronch procedures?
Surrounding healthy lung
How is the CTV defined in endobronch?
A camera (endoscope) is sent through the patient to guide catheter placement
A marker wire specific to that channel will be sent through as well. Once the marker wire is fully through the catheter, the remaining length of the marker wire outside of the TGT is noted (call it ‘E’)
The pulmonologist retracts the camera and on the way out decides the most distal location of the disease
The marker wire is retracted out to match that location. The remaining length of the wire outside of the TGT is noted again, (Call it ‘D’)
The pulmonologist retracts the camera and on the way out decides the most proximal location of the disease
The marker wire is retracted to match that location. The remaining length of the wire outside of the TGT is noted again, (Call it ‘P’)
The distal point is located on the CT following the catheter starting at the end then moving backwards a distance of D - E. Viewing planes are aligned to this point and a point is set.
Similarly, the proximal point is located on the CT following the catheter starting at the end then moving backwards a distance of P - E. Viewing planes are aligned to this point and a point is set. Note: P - E will also be the last dwell location that you enter in the TPS
Then in contouring, use either a 1 cm or 2 cm diameter 3D brush and draw along the catheter from distal to proximal point (edge of contour should be touching the proximal and distal points). This is your CTV. 1 cm would mean 0.5 cm margin, this is for smaller lesions. 2 cm diameter would mean 1 cm margin, this is for larger lesions. At our site we exclusively did 1 cm for everything
In an endobronch HDR with multiple treatment sites/multiple catheters, it can be difficult on the CT to identify which catheter belongs to which channel. What is one work-around to this?
Push a marker wire through the catheter. The marker wires have unique patterns that will appear on the CT. Associate each pattern with the respective catheter/channel number. Mark the TGT in real life accordingly to help distinguish as well (colored markers)
Prior to CT scan of an endobronch, the patient will need to slow breathing in order to reduce motion artifacts. How is this done if the patient is unconscious?
The CRNA nurse controls the breathing period
In theory also, if the breathing cycle can be monitored, which it is, a 4D CT or gated CT can be taken
Why, for most vaginal cylinder patients, is there no uterus?
These patients, atleast in our clinic, are almost always following a hysterectomy before their cylinder treatment
How is cyclinder selection done by the rad onc? Why?
Largest possible cylinder that the patient can comfortably tolerate
This reduces ISL fall off to get to the 0.5 cm target. Thus, the surface of the vaginal wall gets less dose the larger the cylinder is
It also helps to remove air gaps at the cylinder surface
And in some cases for patients with large anatomy, it lets us go deeper
Which cancer are cylinders used to treat?
Endometrial (lining of uterus)
Treated to the vaginal cuff following a curative hysterectomy
What cancer are T&O’s used to treat?
Cerival cancer
Besides gynecological applications, what are some other intracavitary HDR applications?
Endobronchial
Esophageal
Nasopharynx
For endobronchial HDR, why is the catheter inserted as far down the airway as possible?
To anchor it in place in case the patient coughs during treatment. You don’t want the catheter moving
How many channels are typically used for nasopharyngeal and esophageal HDR?
1 channel
It’s usually just a straight shot treatment
Why, for the most part, are esophageal, endobronchial and nasopharyngeal brachytherapy being phased out by IMRT?
An inherent flaw in all 3 of them is that, because of their cylindrical dose distribution, they can only treat small lesions
Disease typically, in most cases, will not symmetrically surround a catheter/entranceway. Thus, if you want to treat large lesions, you need to pump a lot of dose to get coverage, and that results in a lot of healthy tissue getting excessive dose
Which system first defined point A and point B?
The Manchester System
In our clinic, what is the vaginal cylinder prescription point?
Surface of cylinder (that is, 100% of PTV gets prescription dose)
Where the PTV is drawn as an inner wall of the cylinder. So the surface gets prescription dose
What kind of cancer is this?
Endometrial
Label the following diagram
What is T&O used to treat?
Cervical cancers with intrauterine disease for patients who are unsuitable for hysterectomy
Describe the anatomical placement of the tandem
Tandem is inserted as far into the uterus without perfurating the uterine wall
The phlange (thick part of tandem) sits at the cervical os, and is often considered the surrogate for the location of the cervical os
Describe the anatomical placement of the ovoids?
Nested in the vaginal fornices
Made is the tandem made out of? What angles do they come in?
Steel
30, 40, 45, etc
How is the diameter of the ovoids chosen for T&Os?
To be as large as possible while also being comfortable
Same rationale as with cylinders, you want to minimize dose at surface by minimizing effects of ISL while still maintaining required coverage
What is the purpose of balloons used in T&Os?
Packing and dose constraints
Packing - the lock everthing in place in the fornices
Dose constraints - they create separation by moving the ovoids a bit further from the bladder and rectum
How are the right and left Pt A’s defined using the original manchester system? (this is also how we draw at our site)
Align viewing planes such that cervical os is horizontal in both sagittal and coronal planes (which are technically not sagittal and coronal anymore when you re-align)
Go up 2 cm from cervical os following the tandem and 2 cm out
Pt A line should be orthogonal with tandem
How are the right and left Pt A’s defined using the updated manchester system (ICRU 89)?
Align viewing planes such that cervical os is horizontal in both sagittal and coronal planes (which are technically not sagittal and coronal anymore when you re-align)
Connect a line between the centers of the two ovoids
Move superiorly for a distance equal to radius of ovoids + an additional 2 cm following the tandem, then 2 cm out
Pt A line should be orthogonal with tandem
What are the Pt A’s supposed to represent?
The point where the uterine arteries cross the ureters, forming the paracervical triangle
It is thought that the tolerance dose here is the limiting factor, so you give prescription dose to Pt A’s
What is Pt B meant to represent?
Location of obturator nodes (one of the external iliac lymph nodes) and also the pelvic side wall
In general, Pt B dose is also a good measure of the lateral spread of dose
What is the ICRU 89 (updated manchester system), recommendation for how to locate your Pt B’s? What about original manchester system?
ICRU 89: Connect a line between centers of the two ovoids. Move superiorly a distance equal to the radius of the ovoids + an additional 2 cm following the midline
Old Manchester: Same thing, but start at cervical Os and only move 2 cm
Your Pt B line should be orthogonal to midline
What does the rectum point from the manchester system represent?
the point of maximum dose to the rectum
How do you locate rectum point in a T&O plan?
Point marked on frontal radiograph with a line drawn from midpoint of ovoid sources to 5 mm posterior of the vaginal wall
What does the bladder point represent in the manchester system?
Point of maximum dose to the bladder
How do you find the bladder point in a T&O?
Locate the center of the foley catheter ballon, then draw a line to the posterior surface of the ballon. You should arrive at a point in the center-posterior portion of the balloon
Which paper do we reference for our T&O dose constraints?
Ribble GYN (paper by the ABS)
In our clinic for T&Os, why do we not prescribe dose to the CTV?
That CTV is not a real CTV. It’s just a shape that we create that describes the ideal pear shape of our dose distribution. We really prescribe to get prescription dose to Pt A’s
A real CTV would be drawn from potentially an MRI by the physician. They do not draw that pear shaped CTV that we use in TP
In a T&O plan, how do we get the pear shape that we want?
Bravos gives initial dwell time recommendations to get the initial shape pre-normalization
Give first ⅓ of tandem dwells a 15 second dwell time each, and the remaining 10 seconds
Give all ovoid dwell positions a 15 second dwell time
Then normalize to give prescription dose to the Pt A line
The pear shape will be the 100% isodose line, and assuming a Pt A plan, we’re actually done right there
Which ICRU report is the update to the Manchester System?
ICRU 89
Which dose reporting system is recommended by the AAPM?
None is offocially recommended
Per Khan, there is no universal agreement as to the superiority of any one system. It’s a matter of taste, ease, preference and imaging capabilities
BUT, if you can figure out how to delineate the target volume, then ICRU system would be the best
Per ICRU 38, what is the “Reference Volume”
The volume encompassed by the 60 Gy EQD2 isodose line of T&O + EBRT
60 Gy doesn’t have to be used, but that’s what it usually is
What kind of dose reporting for T&O/T&R is recommended by the GYN GEC-ESTRO?
A combination of…
dose to risk level target structures visualized on MRI (GTV, HR CTV, IR CTV, LR CTV)
Total reference air kerma
Pt A doses
Bladder and rectum reference point doses
And OAR volumetric constraints from Ribble
What is the recommended MRI protocol for contouring T&O?
T2
It best visualizes tumor, cervix, bladder, vagina, rectum and sigmoid
T1 may also be used to visualize extent of nodal involvement
What is this?
Rotte “Y” Shaped Applicator
Kind of looks like the fletcher, but isn’t
True or False
The same dose constraints recommended for HDR T&O, are the ones recommended for LDR T&O?
True
As long as everything is converted to EQD2
In comparing T&O vs T&R, which yields a larger treatment volume and has longer treatment times?
T&O
In comparing T&O vs T&R, which has a better Pt A and Pt B dose?
T&O
In comparing T&O vs T&R, which has better dose conformity and thus better OAR dose reduction?
T&R
In comparing T&O vs T&R, which has a better 3D HR-CTV coverage?
T&R
If your T&O or T&R coverage is poor, what is one thing you can do to improve the coverage?
Combine it with interstitial needles
It has been shown that intracavitary + interstitial yields better dose conformity, better reduction of critical structure doses, and better CTV coverage
On a CT, how would you identify a patient who would likely need T&O?
Take a look at the shape of the cervice and uterus
Cervix and uterus should have the shape shown below
If there’s gross disease, it will look “barrel-shaped”
What is one potential downside to starting Pt A tracing based off of the ovoids, as opposed to the flange?
If the ovoids are not snug into the fornices, Pt A will be lower than what it should be
In T&O treatment planning, how would you use opti structures?
Make an opti structure of the CTV standard pear cropped 0mm from all critical structures, then optimize to give that structure 100% prescription dose
It will serve as an anchor to help retain the pear shape, while also removing competeing objectives that will confuse optimizer while you’re trying to lower normal tissue constraints
Briefly describe the ABS recommended dose reporting for T&O
Critical structure 2 cc (we include this)
Pt A dose (we include this)
Bladder and Rectum point doses from ICRU (we don’t include this)
Target D90 coverage (this is shown in DVH so we include it, specifically for the CTV - Std Pear, not the opti!!!!)
At what point can a radioactive source be considered a point source?
When r > 3L
Where L is the active length
What is “midline” when talking about T&O Pt B
Midline is in reference to the orientation of the bony pelvis
Label the following
Don’t be shocked that the uterus and cervix are in the same axial plane, they most definitely can be
Remember, the anatomy is on a slant, it’s not completely inferior to superior
Which of the following is NOT accounted for in TG-43?
Intraseed Attenuation or Interseed Attenuation?
Interseed Attenuation is not accounted for
Intraseed Attention is included in the seed model, and therefore is herently accounted for in TG-43
What are some tests recommended to perform for TRUS per TG-128? (8 listed)
- Grayscale display accuracy
- Depth of penetration
- Axial and Sagittal resolution
- Axial and Sagittal distance scales
- Cross sectional area accuracy
- Volumetric accuracy
- Needle and grid alignment
- Treatment planning computer volume accuracy
What phantom is used for TG-128 annual?
CIRS Model 45 phantom
How is focal spot location influenced by transducer frequency in ultrasound
The lower the frequency, the deeper the focal spot will be
For use of ultrasound, when trying to image an object near the probe, what is best to use, high or low frequency?
High frequency
How is ultrasound depth of penetration influenced by frequency?
Higher frequency is worse depth of penetration
Lower frequency is increased depth of penetration
Which detector type is the detector of choice for experimental determination of TG-43 dosimetry parameters for low-energy photon-emitting brachytherapy sources?
LiF TLD detectors
True or False
It is approprtiate to have a sole GM counter for radiation monitoring during brachytherapy
False
When very high exposures are present, GM meters can register zero exposure. So it’s recommended that a back-up area monitor in conjunction to the GM meter should be present
What are the 4 major types of brachytherapy?
(hint, 1 of them is a subset of another)
Interstitial
Intracavitary
Intraluminal (subset of intracavitary) (blood vessels, bronchus, esophagus or bile duct)
Surface
For beta emitting brachytherapy sources, how is source strength secified?
Activity
What instrument is best for surveying of patients for release criteria?
A calibrated ion chamber
Typically with a large, pressurized gas-filled chamber
Per NRC requirement, what information MUST be present on a inventory log for all RAM?
Isotope
Type of source
Source strength
Location
Why are I-125, Pd-103 and Cs-131 the most commonly used/preferred permanent seed sources? (two reasons)
Low average photon energies and short half-lives
What is the medical term for the patient position in a prostate implant/needle sticking surgical procedure?
Dorsal Lithotomy
In addition to ocular melanomas, what other cancer can be treated with eye plaques? What is the prescription?
Retinoblastomas
40 - 45 Gy in 2 days
What was the COMS original dose calculation assumptions. How have they changed now?
COMS: Assume point source model for seed, no anisotropy, no heterogeneity
Current AAPM recommendations: Use line source approximation, still assume homogeneity
What additional radiation safety concerns are present for eye plaque patients?
Patients stay in hospital during the days of therapy
Housing room must include a radiation sign posted outside of the room
Patient wears special leaded glasses that reduce exposure by a factor of 5 or 6 when visitors or nursing are present
Nurses require annual radiation safety training
What sources are applicable to the Patterson-Parker and Quimby systems?
Both systems were designed for radium implants, so only isotopes similar to radium (such as Ir-192 or Cs-137), may be used with the system. Low-energy sources cannot be used with the syetms
What are some pros and cons to using Cs-137 for HDR instead of Ir-192?
Pros: Cs-137 has a higher average energy that could be beneficial for coverage, and it has a longer half-life (meaning less replacement)
Cons: Higher energy means more shielding, And Cs-137 has a lower specific activity, meaning larger source and larger catheters
Endometrial cancer and vaginal cuff are somewhat synonymous, both are treated with HDR cylinder to the exact same area, for all purposes, they are the same.
Cylinders follow hysterectomies typically however, so why do you still give radiation when the uterus is gone?
Vaginal Cylinders are prophylactic. They are meant to reduce recurrences by irradiating the vaginal cuff
If there’s one thing you should remember, it’s that endometrial and vaginal cuff are synonymous and often times used interchangeably when talking about cylinders
What anatomical site is treated with cylinders?
The dome of the vagina (typically upper one-third to one-half
True or False
The dose constraints to critical structures used for T&O are exactly the same as would be used for a cylinder?
True!
We usually never even mention it because cylinder doses are so low to the critical structures, but yes, they are the same constraints
In what clinical situation would solely interstitial brachytherapy be used for GYN cancer?
With recurring endometrial and cervical cancers post hysterectomy that relapse after surgery in and around the vaginal cuff area with a depth greater than 5 mm
To deep for cylinder, no place for tandem
In what clinical situation would solely interstitial brachytherapy be used for GYN cancer?
With recurring endometrial and cervical cancers post hysterectomy that relapse after surgery in and around the vaginal cuff area with a depth greater than 5 mm
To deep for cylinder, no place for tandem
What is this? What is it used for?
Capri applicator
It’s a multi-lumen (13), inflatable balloon applicator that can be used in place of a vaginal cylinder for treating vaginal cuff/endometrial cancers. Gives more dose shaping capabilities.
Inserted in patient then inflated to fill space
What is the construct difference between contura, savi and mammosite?
Contura - balloon with multiple curved channels on the inside, 1 straight channel in center. Curved like savi, but they’re rigid, they don’t change curvature.
Mammosite - balloon with 1 or more channels, all channels are straight. For multiple channels, you have one channel in center, others surround
Savi - no balloon, curved channels fit the cavity and touch the tissue
Between contura and mammosite, which can give the best dose conformity? Why?
It depends…
What you care about the most is the separation of the channels. For contura, the separation of your channels is very slightly greater than mammosite near the center of the applicator. BUT, at the ends of the applicator, the channels meet back for contura, meaning the modulation is worse at the ends than mammosite
True or False
Contura has different dose constraints than mammosite and savi?
False. It should actually be…
Savi has different dose constraints than mammosite and contura. Specifically for target dose constraints. That’s because with Savi the source is touching the tissue, so some hot spots are impractically difficult to avoid
Why did we stop doing IORT?
Study that physicians read showed that local control for IORT was poor compared to EBRT boost
Why did we stop doing savi?
Since channels can be deformed and bend so drastically, it became an integrity scare
Why did we stop doing accuboost?
Inconvenient, long, needed physician present the entire time, uncertainty in breast moving, and we need surgical clips ahead of time
Why did we stop doing contura/mammosite?
We preferred EBRT which is easier
What loading technique did we used to use for LDR prostate?
We used stranded seeds with spacers are the end. This allowed us to insert all seeds starting at the same depth. This is called baseline loading
What imaging modality did we use for LDR pre-planning prostate?
TRUS
Most places use it
Which imaging modality will yield the largest target contour, CT or TRUS?
CT
Because you need to do some slight over-estimating
If you have air vs water within a few cm of your source, why do you really not care dosimetrically speaking?
In the first few cm from source, ISL dominates, and that is medium independent
Although it is true that water will have more attenuation, the loss in dose due to attenuation is roughly compensated by the increase in dose due to scattering. So dose in water will still be close to dose in air for the first few cm
What is the procedure for taking a pre-plan LDR volume study done at our site?
TRUS, on stepper, with imaginary grid, no anesthesia
Begin at the deepest depth to find the base of the prostate
Step out at 5 mm increments to obtain slice by slice in the axial
When we used to do LDR prostate, what structures did we contour?
Only the prostate (CTV) + a 3 mm margin (PTV)
We did not analyze urethra and rectum wall volumetrically, we only accounted for them in seed placements visually
What isotope, manufacturer and seed model did we used to use for LDR prostate?
Theragenics
I-125, AgX100 model
We tell theragenics the activity and the date of activity that we want a batch from
For LDR prostate seed placement, what rules did we follow?
1 cm seed separation in all directions
Do not place any seeds on ‘D’ column because urethra will be there
Avoid placing seeds on row ‘1’, rectum will be near there
A needle needs to have at least 2 seeds
Needles must be within the prostate (only exception is end slices if the volume on the slice is too small to keep them within)
Note: If after following these rules, coverage is not met, you can increase the source activity that you want to order
Note: even if your DVH numbers are met, you need to make sure that the isodose lines look good, (no missing coverage, no bowing in, no high dose to rectum or urethra, etc.)
Why is a minimum distance of 1 cm required for seed separation?
The seeds are titanium, but TG43 (which we use in our calcs), does not take into account attenuation due to the material of a nearby seed
At distances of 1 cm or more, the uncertainty in dose calc becomes small enough that we’re comfortable
For our LDR prostate program, what were all the dose constraints?
Prostate D90% > 100% (>95% variation)
Prostate V150% < 50%
Note: We did not have a urethra or rectum constraint because we never contoured them
For an LDR prostate procedure, what happens when your patient is delayed by a day relative to your plan? Do you abort?
Consult with the physician. For I-125, 1 day is a little more than 1% loss in activity
Not the end of the world, they’ll likely be fine with it
Why for LDR seed ordering, do we always order extra strands?
In the case of the prostate growing between the pre-plan and the day of, we want extra strands to be able to get coverage. Or in the case of a strand being pulled out by urologist during cystoscopy
Also for assay we get a single extra seed. This is because the theragenics strands are sterilized and pre-loaded. Theragenics will assay the rest
For Variseed planning, where is the source position defined?
At the center of the active length
What calibration coefficient is given by ADCL for the well-type chamber? What are the units? What is the approximate order of magnitude?
Air Kerma Strength Calibration Coefficient
Gy m2 / Ampere hr
Order of magnitude: 105
What are the units of the conversion factor? What does it convert? What is the equation to derive it?
uGy m2 / hr mCi
Converts air kerma strength to activity
CF = (Γ * w/e)-1
What is the name of the well chamber we use?
Standard Imaging HDR1000 Plus
Our source calibration time is 12 PM, but the source calibration time we enter into the console is 1 PM, why is that?
Alpha-Omega calibrates the source in Louisiana (CST)
So 12 PM CST = 1 PM EST
So we tell our console that it was calibrated at 13:00 local time
How would you measure channel length using the racetrack?
Before attaching TGT to needles, use a small wire to check consistency of length among all needles, and also to check for obstructions
Then attach TGTs to needles
Then run a wire through to the end of a needle, use a screw to signal end of TGT, then remove and run through racetrack, stopping at the screw, to measure the length
Doing this for every single channel for a prostate can be very time consuming, so most people only check for a random sample of 5 or 6
This is fine since you checked needle constancy earlier, and also all TGTs have the length noted at time of commissioning
Which isotope is used to treat Xofigo? And what is Xofigo used to treat?
Radium-223 (HL 11.4 days)
Used to treat prostate cancer that has spread to the bone that no longer responds to hormonal or surgical treatment (treats the bone metastasis)
Which softwares are FDA approved for dose calculation for Pluvicto and Lutathera? What about Y90?
Pluvicto and Lutathera - MIM
Y90 - Velocity
For LDR seed inventory, how did we measure activity of the source on the day of survey?
We didn’t. We used decay calculation to find activity
All we did was survey
How many half-lives did we store I-125 for?
10 half lives
But we would also check at 7 half lives, and if survey is slightly above background, we could release in theory
Is patient release calculations for lutathera based off physical or effective half-life?
Physical half-life
So it’s actually more conservative, since effective half-life, which is more accurate, would mean you are getting rid of the isotope quicker, so patient release can actually be lower than what we have it
We use 2.1 mR/hr release for Lu-177, but what do most other places use?
2 mR/hr
So we’re actually more liberal in that sense
True or False
Since patient release is based off effective half-life, Lutathera and Pluvicto will have different patient release criteria?
False
Release if based off physical half-life, so in theory Lutathera and Pluvicto will have roughly the same release
For Bravos, what is the allowed channel lengths for the system? What happens if length is > tolerance + length, what happens if it’s < length - tolerance?
[designated channel length in plan] +- 2 cm
Let’s say for example. Ch length = 150 cm
If length measured is > 152, bravos assumes there is no channel end and retracts the source, not allowing you to treat
If length measured is < 148, bravos will detect it as a blockage and retract
Why is there a channel length +- 2 cm tolerance for bravos? Where does that 2 cm come from?
That’s the distance prior to programmed channel length that the bravos afterloader starts to slow down the dummy wire
True or False,
For endobronch, the patient may be awake.
This is TRUE
In fact many sites have the patient awake as it is generally easier. BUT, it introduces more uncertainty
True or False,
Endobronch HDR is good for treating all bulky tumors in bronchus?
False
It’s only good for treating bulky disease that symmetrically surrounds the catheter
What is the functional difference between the slave monitor and the master monitor?
The master monitor has a radiation detection volume in it
The slave monitor has no radiation detection volume, all it does is receive the signal from the master monitor so it can start blinking inside the console area
What is the prescribed activity for pluvicto?
Something very slightly under 200 mCi
With SAVI, how can you tell on a CT which channel is which?
The SAVI applicator has a metal mark at the middle part of a known channel. From there you number them clockwise
And channel one for SAVI is always the central channel
Why don’t we do a wipe test when receiving the Ir-192 source?
- Manufacturer does a wipe test of package at time of manufacturing and packaging
- Engineer does ANOTHER wipe test at time of source exchange
- It’s a sealed source, it’s very unlikely that anything would change throughout shipping. So it’s very unlikely that your wipe test would show anything that the prior wipe tests wouldn’t show
- And also, we measure activity on surface with a survey meter, it would touch any existing contamination, and it would show as the signal not going away as you move away from the container
What contamination might be present from the Ir-192 source?
Possible shavings, or bits of the source that are present in the air to get on the container or the wire
How is Ir-192 produced?
Neutron bombardment of Ir-191 (which is a naturally occuring stable isotope)
What is the decay of Ir-192?
Ir-192 → Excited Pt-192 (95%) (beta minus then gamma emission)
Ir-192 → Excited Os-192 (5%) (electron capture then gamma emission)
What MRI protocol do we use for HDR prostate?
T2
True or false
For prostate HDR, the bladder is filled right before sim, and right before treatment delivery
False
The bladder is filled before the patient ever reached rad onc. From there the drainage is clamped so it doesn’t drain
Where is dwell position defined for our source model in brachyvision? What about variseed?
Brachyvision: End of weld tip
Variseed: center of seed/active length
What is the distance from active length to tip of wire/seed for our model Ir-192 seeds?
0.7 mm
For cylinders, would you want a seed with a smaller or larger weld tip?
You want smaller weld tip, that way the active length is closer to the end of the cylinder and you can get coverage easier
What Ir-192 seed model do we have? What is the active length, what is the length of the tip?
GammaMed plus
- 5 mm active length
- 7 mm
Why does bravos specify no dwells ≤ 0.3 seconds
Because bravos corrects transit times. So what ends up happening is some seconds are subtracted off from a given dwell position
Below 0.4 seconds, subtracting off for transit dose gives a negative dwell time, which is an error in the system
What is the concept behind a HDR universal plan?
Assume 10 Ci is the day of strength, then scale on the machine
Many places do this
For us, however, we do not do this for two reasons.
- It’s an extra step, which means extra possible chance of error
- If a dwell time ends up being >0.4 s for a 10 Ci plan, but your source is actually over 10 Ci, then you get the transit time issue
For Bravos, what is the function(s) of the dummy wire?
- Make sure there are no obstructions before sending out the source wire
- Measure channel length, and adjust plan relative to the difference. Ex. if the plan says that the end of a tandem is 150 cm, but Bravos, based off their measurement, says its 150.2 cm, then all positional data for the source cable will be adjusted by that .2 cm difference to agree with real conditions
For all other systems besides Bravos, what is the function(s) of the dummy wire?
To make sure there are no obstructions before sending out the source wire
How does Bravos determine dwell location mechanically?
Most likely based off pressure or tension of wire and a calibration curve
How do other afterloaders besides Bravos determine dwell location mechanically?
They wheel out the wire to the very end, retract back a certain distance to remove slack, and that distance is calibrated to a certain value. Then they wheel from there and know the relative wheeling length
What is the purpose of PVT?
To make sure that what the machine thinks is a position, is true
Why do we measure the difference between dummy wire and source wire during morning QA and why do we use such a tight tolerance?
- Because we can, it’s very easy to measure and calibrate with bravos
- Because bravos adjusts source positioning based off dummy wire before treatment, so you would hope that the two wires agree very closely to one another
True or False
As part of annual, we measure the actual lengths of the ruler that is used in the bravos PVT test
False
We assume that the ruler is accurate and that engineering/installation has already checked this. This is purely an assumption
Per Dr. Wei, why do all HDR systems define dwell position as the physical tip of the wire?
So you can also define the deepest location of the wire to equal the channel length
Why for varisource is the first dwell location 0.3 cm, but for bravos it’s 0.1 cm?
Varisource measures distance based off sending the wire to the very end, then wheelign it back. The wheeling back requires a little bit of distance to remove slack
Bravos goes off pressure or tension and in theory doesn’t actually need the 0.1 cm, that 0.1 cm is just recommended for safety so the source doesn’t ram into the tip
DoseCheck most likely uses the same tables that TPS uses for their dose calcs. In that case, why is the agreement not 100%?
Tables are continuous, so there can be interpolation discrepancies
Dose grid size can make a huge difference as well
Location of origin of seeds make s a difference as well
What kind of agreement between TPS and Dosecheck would you expect for gamma and point dose for HDR cases?
Point dose: within 1%
Gamma: nearly 100%
If your physician approached you and wanted to begin a new HDR procedure at your site, what are some things you want to consider when commissioning the program? (8 things listed)
- Read up on background information
- Determine budgeting and required devices/equipment
- Consider logistics (sim, scheduling, OR involvement, implants, etc.)
- Develop a multidisciplinary standard operating procedure (SOP) for the parties involved
- Develop an SWI as needed for role specific
- Acceptance test the device
- Perform an end to end
- Get some practice planning some test patients
What is hysteresis?
It is the idea that if you measure the exact same thing, 2 different ways, you can get different measurements
Ex. If you measure dwell position by sending cable all the way to the tip and retracting back, versus measuring location based off wheeling rotations, you will likely get two different results
What is the alternative to using balloon packing for T&O?
Gauze packing
This is not preferred as gauze can dry up and is not as comfortable
Label the following blanked out parts
Which type of treatment would result in more normal toxicity (if the same tumor effect is maintained with no change in geometry)? HDR or LDR?
HDR
