TG59 Flashcards
What is TG59 on?
HDR brachytherapy
advantages of HDR vs LDR
-patients are usually outpatients
This point is especially relevant for gyne brachy where long hospital stays were required to deliver adequate dose with LDR or PDR (source comes out for e.g., ~5 minutes every hour, requiring a 48 hours hospital stay).
-patients are not radioactive after treatment
-more stable positioning because less time therefore less movement
-also, seeds may shift during LDR due to prostate shrinking etc
o Having a single HDR source is easier to keep track of than a shipment of one-time-use sources; no need to wait on a shipment of new sources, do activity spot check, and possibly also manually arrange seeds into strand in preparation for treatment (some clinics purchase pre-made strands).
o With temporary implant prostate HDR, catheters can be safely implanted outside the prostate and in the seminal vesicles without the risk of seed migration (relevant for patients with ECE = extra capsular extension). Also, it may be difficult to treat patients who have had transurethral resection of the prostate (TURP) with LDR seeds due to missing tissue – not an issue with HDR since catheters provide a stable path for the seeds
downsides of HDR compared to LDR
-high dose rate- consequence or errors is greater
o Potential for serious errors due to more unforgiving nature of the treatment due to high dose rate.
o Due to the high dose rate, remote afterloaders need safety interlocks; overall the system is more complex than an LDR system; longer training period for staff.
o Greater room shielding requirements for HDR, depending on the energy of the source.
o The procedure needs to proceed quickly (stressful environment) to avoid patient motion, and to minimize expense and risk associated with anesthesia, if used.
o Due to high dose per fraction, normal tissue toxicity is a concern.
o There is potential for very high radiation doses to patients and staff in the event that the source fails to retract.
describe the remote afterloader
since Ir-192 source is welded to end of flexible cable
cable is connected to channels which are connected to transfer tubes
the transfer tubes connect to applicators that are implanted in the patient
describe Ir-192 source in remote afterloader
diameter 0.3 to 0.6 mm
length 3.5 to 10 mm
activity 10 Ci
pros and cons of using a remote afterloader
With the use of a remote afterloader, there is reduced radiation exposure to health care providers compared to hot loading. Also with remote afterloading, there is the potential for more consistent and reproducible treatments. Dose distributions may be optimized beyond what is possible with manual afterloading (due to ability to step the source through the patient)
remote afterloading devices are expensive; they are complex devices requiring detailed commissioning and QA procedures, and more training for staff.
can remote afterloading be used with HDR or LDR?
Yes
therapists’s pre-treatment QA checks
o Applicator inventory: check that all necessary applicators and accessories are available, sterilized, and in good working order (e.g., not broken, cracked, bent or rusty).
o Correct template is ready (check hole diameter)
o Any other equipment necessary should be ready in the operating room (e.g., sterile gloves)
o Remote afterloader: perform daily QA
- QA during applicator insertion
-QA during radiographic exam
daily QA for remote afterloader
Door interlocks e.g., source retracts when door opened
Treatment interrupt and emergency stop buttons
Unit survey plus survey of patient before and after treatment
Source positioning/timing check
Emergency equipment checklist e.g., bed crank, lead pig, tools for removing applicator
Independent radiation monitor and its battery backup.
Functioning audio-visual monitor of patient
Afterloader connection interlock
Audio-visual treatment status alerts.
what is the QA during applicator insertion?
o Applicator type and dimensions checked prior to insertion.
o Applicator adapters/clamps should be correctly assembled.
o Record of treatment: which applicators/needles were inserted and where.
what is QA during radiographic (or US or MRI) exam of the implant
o Check that radiographic markers are correctly inserted.
o Image quality is adequate for clinical evaluation of applicator/needle position/orientation, and for contouring (can identify necessary structures); radiographic markers are visible.
dose rate of HDR vs LDR
up to 12 Gy/h vs 50 cGy/h
typical dose rate for HDR is 0.5-1 Gy/min for a new source
examples of reportable issues in brachy
- deliver to wrong patient
- using wrong isotope
- treating wrong site
- using leaking sources
- failing to remove a temporary implant
- delivering radiation dose that differs more than 20% from prescription dose
advantages of HDR compared to LDR
- better optimization of isodose distribution to shape of treatment volume
- outpatient treatment
- more stable positioning (immobilized applicators and patient anatomy won’t change over treatment)
- smaller applicators in gyne
- reduce radiation exposure to health care workers
disadvantages of HDR compared to LDR
-more serious consequences for errors
(technical difficulty and compressed time frame mfor large fraction dose)
-treatment systems require safety interlocks
-Radiobiologically, HDR
treatment may be expected to result in more normaltissue
toxicity than LDR treatments, if the same tumor
effect is maintained with no change in geometry. Many
years of use will be required to determine the successful
use of HDR.
-Increased need for accurate dosimetric, anatomic and
geometric information. Maintaining doses below levels
that would compromise healthy tissues ~being more at
risk than with LDRB! requires more accurate anatomic
and geometric information.
-high radiation dose to staff if source doesn’t retract
what makes an error systematic?
~1! no individual lapse of judgment or failure to adhere
to procedure was the cause and ~2! all patients treated according
to these flawed procedures are at risk for similar
treatment delivery errors
examples of systematic errors
-using wrong diameter colpostat
discrepancy between time standard for calibration and time of remota afterloader that isn’t accounted for
-wrong length of transfer tube
-usually these errors are caused by inadequate QA
examples of random errors
- transient device malfunction
- team member doesn’t follow protocol
- making a mistakge
- relying on policies and procedures that don’t represent unusual situations
principles of HDR brachy program design
-use written documentation
-develop a formal procedure
-exploit redundancy (isolate the vulnerable actions and decision
points where mistakes could result in serious dose delivery
errors. Each key step and essential piece of information
should be independently verified)
-exploit quality improvement techniques (assess adequcy and introduce improvements)
what is IRAK
integrated reference air kerma
product of air kerma strength and dwell time
uGy m^2 or cGy cm^2
how long to start a new HDR program?
2-4 months for an experienced HDR physicist (full time)
time allocated to a MP to do 10 fractions per week
a full time physicist
use of a 2nd computer to check calcs?
not super useful since most errors are due to humans not entering data properly
2nd check of dose calc
-can use quick calculations to see if computer calcs are sensible. RadCalc
