Test 2 Flashcards by Courtney W

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

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Geometric definition of position and extent of tumor volume and critical normal structures by using x-ray, CT, MRI and/or PET

Localization

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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

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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

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Measurement with calipers of a patient along the central axis or at any other specified point within the irradiated volume

Separation

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Dimensions of treatment field at isocenter determined by the collimator opening in simulation software, treatment planning system, and on the treatment unit

Field size

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2D image reconstructed from CT data that shows a beam’s eye view of the treatment field created at isocenter

Digitally reconstructed radiograph (DRR)

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Change in target position from one fraction to another due to setup error, change in marks, etc.

Interfraction motion

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Change in target position during treatment delivery; ex: respirations in thorax, gas in bowel, etc.

Intrafraction motion

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Palpable/solid tumor, macroscopic disease; different margins created in treatment planning computer

Gross tumor volume (GTV)

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GTV and surrounding volume of tissue that may contain subclinical or microscopic disease too small to visualize

Clinical target volume (CTV)

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CTV plus margins for geometric uncertainties; ex: patient motion, treatment setup differences (distance change, etc.), and penumbra

Planning target volume (PTV)

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Outer edges of radiation beam less intense

Penumbra

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CTV plus an internal margin that accounts for tumor motion; ex: gating for lung

Internal target volume

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Volume of tissue receiving a significant dose (over 50%) of the specified target dose

Irradiated volume

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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

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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

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Distance from target of radiation to the imager

Target-image receptor distance (TID)

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3 commonly used contrast media

Barium Z #56 (drink a lot of water)
Ionic or nonionic iodinated Z #53
Negative: air

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About ____% of anaphylactic reactions happen in about 5 minutes; usually occur within ____ min

70%; 30 min

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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

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When to use contrast for brain

IV push 10-30 minutes before scan because tumors are very vascular

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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

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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

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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

3 cm lateral of point A, 5 cm lateral to patient's midline

1 cm further lateral to point B

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