Test 2 Flashcards
Process carried out by therapist under the supervision of the radiation oncologist; part of treatment planning procedure, which delineate the treatment field and construct any necessary immobilization or treatment devices
Simulation
Geometric definition of position and extent of tumor volume and critical normal structures by using x-ray, CT, MRI and/or PET
Localization
Final check to ensure each of the planned treatment beams cover the tumor or target volume and don’t irradiate critical structures; port films
Verification
Small markers are often used to mark specific points on a patient during CT; ex: vaginal or rectal, wire for breast or scars (seeding)
Radiopaque marker
Measurement with calipers of a patient along the central axis or at any other specified point within the irradiated volume
Separation
Dimensions of treatment field at isocenter determined by the collimator opening in simulation software, treatment planning system, and on the treatment unit
Field size
2D image reconstructed from CT data that shows a beam’s eye view of the treatment field created at isocenter
Digitally reconstructed radiograph (DRR)
Change in target position from one fraction to another due to setup error, change in marks, etc.
Interfraction motion
Change in target position during treatment delivery; ex: respirations in thorax, gas in bowel, etc.
Intrafraction motion
Palpable/solid tumor, macroscopic disease; different margins created in treatment planning computer
Gross tumor volume (GTV)
GTV and surrounding volume of tissue that may contain subclinical or microscopic disease too small to visualize
Clinical target volume (CTV)
CTV plus margins for geometric uncertainties; ex: patient motion, treatment setup differences (distance change, etc.), and penumbra
Planning target volume (PTV)
Outer edges of radiation beam less intense
Penumbra
CTV plus an internal margin that accounts for tumor motion; ex: gating for lung
Internal target volume
Volume of tissue receiving a significant dose (over 50%) of the specified target dose
Irradiated volume
Difference between SSD and SAD setups
Changing isocenter; SAD at depth, SSD to skin
SSD requires more MUs because it’s further from treatment and have to move patient every time we move to new field
Two films taken at right angles/90° to one another; gives more information about depth and can see superimposed structures (ex: four field pelvis)
Orthogonal films/orthogs
Distance from target of radiation to the imager
Target-image receptor distance (TID)
3 commonly used contrast media
Barium Z #56 (drink a lot of water)
Ionic or nonionic iodinated Z #53
Negative: air
About ____% of anaphylactic reactions happen in about 5 minutes; usually occur within ____ min
70%; 30 min
When to use contrast for head and neck
Power injector seconds before scan to highlight vessels and distinguish them from lymph nodes (LN) or mass
When to use contrast for brain
IV push 10-30 minutes before scan because tumors are very vascular
When to use contrast for liver (abdomen)
Power injector 20-40 seconds before scan to visualize hepatic arterial phase and 60-90 seconds before to see venous phase
3 contrasts used for pelvis
IV push at least 15 minutes before scan for prostate to highlight bladder
Radiopaque marker for rectum (critical structure)
Barium 30-60 minutes before to see small bowel
3 contrasts used for GI tumors
Barium paste to coat esophagus
Dilute barium sulfate solution to highlight stomach or small bowel
Barium 30-60 minutes before to see small bowel
Deliver high dose to small volume, usually the GTV only, excluding regional lymph nodes or OARs
Boost fields
2 methods of CT simulation
Shift method
No-shift method
Reference marks placed on patient before CT
Later physician/dosimetrist determines treatment isocenter coordinates
Shifts between the marks placed on the patient while they’re on the CT scanner and the treatment isocenters are calculated
Initial reference marks removed and new treatment isocenters are marked on patient
Zero out isocenter
Shift method
Patient scanned and while patient is on couch, images reviewed by doctor and the treatment isocenter is determined based on the areas contoured on the images; isocenter coordinates programmed into the moveable lasers in scanner room and patient is marked accordingly
No-shift method
Patient has coordinates related to table they’re at every treatment
Registering/indexing patient to table
Respiratory gating currently used to account for moving tumor volumes
4D CT
Provides physiologic function by using the beta decay radiotracer 2-fluoro (fluorine 18) fluoro-2-deoxy-D-glucose (FDG) which accumulates in organs with high glucose utilization, which occurs in areas of more metabolic activity such as disease sites
Can be fused with CT acquired during simulation and used for treatment planning; maintains position which is very desireable
Positron emission tomography (PET)
Offers better soft tissue contrast and resolution than CT but inherently has some geometric distortion
MRI
External representation of patient’s surface/topography
Contour
4 contour devices
Lead solder wire
Plaster of paris
Aquatube
CT (best)
CPR compressions to breaths ratio
30 compressions : 2 breaths
Process of aligning multiple data sets into a single coordinate system so that the spatial locations of corresponding points coincide
Registration
5 types of image-guided radiation therapy (IGRT)
Ultrasound (around 2000, prostate) On-board imager (OBI) Exac Trac from BrainLab CT-on-rails Cone beam CT (CBCT)
kV imager provides better soft tissue contrast than MV (depends on electron density)
Generally only used to view anatomy because it has different geometry than treatment
Mounts x-ray unit and IR system by using robotic arms on the accelerator gantry at 90° from electronic portal imaging device (EPID)
On-board imager (OBI)
Not attached to the accelerator and uses two floor-recessed x-ray units and two ceiling mounted amorphous silicon flat panel detectors
Images from system can be analyzed and couch corrections calculated to position the patient before treatment
Infrared tracking system used to track patient during treatment
Exac Trac from BrainLab
CT in treatment room
Accelerator treatment table rotates 180° and CT unit moves on rails while patient is imaged with couch in a stationary position
CT-on rails
At certain degree intervals during rotation of gantry single projection images are acquired; ex: 1°
These different angle images are slightly offset from one another and are the basis upon which 3D volumetric data sets are generated
Net result is a 3D reconstructed data set, which can project images in three orthogonal planes (axial, sagittal, and coronal)
Final product is 3D data set with patient in treatment position
Cone beam CT (CBCT)
MV imager, photoelectric depends on Z^3/E^3 = grainy images
Electronic portal imaging device (EPID)
2 forms of respiratory motion management
Abdominal compression
Gated treatments
Respiratory cycle
Adult at rest breathes in and out 12-16 breaths per minute
Tracks tumor and radiation is turned on when the target is within the treatment volume and radiation is turned off when target is outside target volume
Increases treatment time
Gated treatments
2 gated treatment devices
Real time positron management system (RPM)
Electromagnetic transponder near x-ray tube reads movement 10-12 times per second by using electromagnetic detector system
Lesions in lower lobe of lung movement as much as ____ mm in the superior inferior directions and as much as ____ mm in the AP and left and right lateral directions
Lesions in lower lobe of lung movement as much as 12 mm in the superior inferior directions and as much as 5 mm in the AP and left and right lateral directions
In a study of 22 patients, 10 showed no tumor motion in the superior-inferior direction, in remaining 12 patients. ___-___ mm motion
3-22 mm
Therapy that delivers nonuniform exposure across the radiation field using a variety of techniques and equipment
Intensity modulated radiation therapy (IMRT)
Therapy that with the use of 3D treatment planning, allows the delivery of higher tumor doses to selected target volumes without increasing treatment morbidity; set specific shapes in and around a volume to exclude critical structures
Conformal radiation therapy (CRT)
Used to define a coordinate system in the treatment planning and delivery process
Fucidals
4 IMRT delivery methods
Physical modulators: brass block, .decimal pieces
MLC’s: bimodal - open or shut
Arc therapy
Fan beam
2 types of MLC’s
Static
Dynamic
Machine turns off when field moves
Static MLC
Constantly moving MLC
Dynamic
Radiation therapy delivered while the gantry moves through its arc of rotation, thus effectively delivering radiation through a continuous sequence of individual overlapping treatment portals; ex: ion linacs
Arc therapy
Treatment unit where the linac rotates continuously while the treatment couch moves through the gantry bore producing a spiral treatment beam
First treatment machine capable of spiral/arc therapy
Like CT but has the 6 MV tube in it
Tomotherapy
Fan beam
Lower dose of radiation is released at the surface but a sharp burst of radiation is released as the beam reaches the tumor site
Stops at the tumor, leaving the healthy cells beyond it unaffected
The beam can be contoured to the exact shape of the tumor, further decreasing radiation exposure and limiting side effects
High dose to tumor volume near critical structures
Proton therapy
Sum of several individual Bragg peaks at staggered depths that provides a useful beam over a greater range in patient; maximum energy can treat the entire tumor from the most distal to proximal edges
Spread-out Bragg peak (SOBP)
8 times radiation therapy with protons can be used
CNS Prostate (right and left lateral) Lung Ocular Head and neck Esophagus Pediatric Retreatment possibilities (limit dose to previously treated area)
Placing the radiation sources in or at close proximity to the treatment volume and away from normal tissue, very high tumoricidal doses of radiation can be delivered to the target area while sparing surrounding tissues and organs at risk (OARs)
Isotopes placed right up against tumor/islands at very high dose close to proximity to radiation
Short amount of of time, treatment at a short distance
Supplemental boost treatment
Up to 100 Gy
Immediate
Low dose to critical structures because it falls off rapidly
Brachytherapy
Time source is in body determined by activity, etc.
Dwell time
4 applications of brachytherapy
Interstitial
Intraluminal
Topical/surface
Intracavitary
Placement of radioactive sources directly into a tumor or tumor bed; commonly used in neck, breast, prostate, and soft tissue sarcoma treatment (ex: catheters in breast or skin)
Interstitial brachytherapy
Placement of radioactive sources in body tubes such as esophagus, trachea, bronchus, and endometrium via catheters
Intraluminal brachytherapy
Placement of radioactive sources on top of area to be treated; ex: skin, eye plaque, etc.
Topical/surface brachytherapy
Placement of radioactive sources within a body cavity; ex: cervical
Intracavitary brachytherapy
3 roles of source strength
Provides a commonly accepted means for measurement when describing quantities of emitted radiation
Provides practitioners dose calculations
Serves as a prescription basis
Rate of decay
Quantity of radiation emitted from the source to be used; describes strength of a source
Number of disintegrations per unit time
Activity
Traditional unit of activity; 1 gram of radium
Curie (Ci)
SI unit of activity
Becquerel (Bq)
1 Ci = ? disintegrations per second
3.7 x 10^10 disintegrations per second
1 Bq = ? disintegrations per second
1 disintegrations per second
3.7 x 10^10 Bq = ? Ci
1 Ci
Total number of atoms that decay per unit time
Radioactive decay
Decay constant
λ = 0.693/half-life
Decay constant and activity are ________ while half-life and activity are ________ (takes longer = less activity present)
Proportional; inversely proportional
Activity formula
At = Aoe^-λt
Ao = initial source activity At = activity after time
Average lifespan for decay of radioactive atom/source
Know when last half-life (T^1/2) of permanent implant is
Mean life
Mean life formula
T^1/2(1.44)
2 permanent implants
Gold-198
Iodine-125
First isotope used in brachytherapy, equivalent substitutes used today
Brachytherapy sealed, encapsulated
Radium
Disadvantage of radium
Daughter product radon can leak as gas and be harmful because of its high specific activity
Activity per unit mass of radioactive material
Specific activity
Actual length of source (shorter/smaller)
Active length
Capsule length (longer)
Physical length
Measures air kerma strength
Exposure rate
Mass of radium required to produce the same exposure rate at 1 cm from the substitute source
mg-Ra-eq
1 mg-Ra-eq = ? mCi
0.98 mCi
3 methods for applying brachytherapy
External/mold applicators
Interstitial applicators
Intracavitary applicators
Surface lesions requires higher localized doses; ex: eye plaque
External/mold applicators
2 interstitial applicators
Permanent
Temporary
Interstitial applicators used when tumor is inaccessible; deep-seated tumors like lung, abdomen, pelvis, etc.
Permanent
No body cavity or orifice to accept source so it’s placed near tumor and removed later
Temporary interstitial applicators
3 intracavitary applicators
Tandem and ovoids
Heyman capsules
Vaginal cylinders
Intracavitary applicator inserted through cervical os into endometrium/uterus
Tandem
Intracavitary applicators set in fornices of cervix
Ovoids
Intracavitary applicator in uterus, can be used with tandems (only one point of source) and offers the best dose distribution
Heyman capsules
Used for uveal melanoma of eye (most common eye CA but rare)
Stitched and placed in eye
Source: Iodine-125 (low energy)
Thin layer of gold on outside shields radiation from getting out
5000 cGe (cGy equivalent because it takes alpha beta ratio into effect/biological effect)
Only takes a couple days
Eye plaque
Measures length of uterus (don’t want to perforate it)
Uterine sound
Histometer
Fletcher suit
3 hand calculations
Paterson-Parker/Manchester system
Quimby/Memorial system
Paris system
Uses nonuniform distribution of radioactive material and produces a uniform dose distribution based on how sources are placed in patient
+/- 10% accurate
Uses specific points: A, B, P, rectum, and bladder
Paterson-Parker/Manchester system
2 ways to calculate Paterson-Parker/Manchester system
Planar implants
Volume implants
Sources in order, calculation based on shape
Planar implants
Representation of sources takes specific shape
Volume implants
Uniform distribution of activity within the implant; 1 cm apart
Rectilinear
Quimby/Memorial system
Uses uniform distribution of the radiation sources like Quimby; rectilinear
Paris system
Distance paths/lines which are always parallel to the axis at right angles
Recitlinear
Used today, can be checked by hand calculations
Computer calculation method
2 cm lateral to the midline of the cervical canal/tandem/patient 2 cm superior to cervical os/end of the tandem
Can go from midline of tandem because patient’s cervical canal may not be exactly midline
Uterine vessels cross ureters at this point; critical structures that limit dose
A
3 cm lateral of point A, 5 cm lateral to patient’s midline
B
1 cm further lateral to point B
P
At point of foley catheter
Bladder
5 mm posterior to vaginal wall
Rectum
Tandem and ovoids distribution ______-shaped because of ovoids; get better coverage
Dose falls from inside-out
Pear
Measures uniformity of dose
Autoradiograph
