MOSBY ONLINE - TREATMENT PLANNING Flashcards
(226 cards)
1
Q
Tissue compensators are used to:
A. provide uniform dose distribution in tissue deficit areas
B. delineate field arrangements in soft tissue
C. register patient position during treatment
D. shape the treatment field around the tumor
A
A. provide uniform dose distribution in tissue deficit areas
Rationale:
Tissue compensators are used in areas where there are tissue deficits. The compensator helps provide uniform dose distribution in this area.
2
Q
A dose of 300 cGy was to be delivered to the thoracic spine at 95 cm SSD. An error caused treatment to be given at an SSD of 92 cm. The actual dose delivered was:
A. 281
B. 291
C. 320
D. 341
A
C. 320
Rationale:
The inverse square law applies here. 300(95/92)subscript2 = 320.
3
Q
While treating lateral fields in the treatment of the craniospinal axis, to avoid having the caudal margin of the lateral fields diverge into the posterior spine field, the couch should be rotated:
A. way from the collimator
B. toward the collimator
C. until the table is at 5 degrees
D. until the table is at 10 degrees
A
B. toward the collimator
Rationale:
To prevent divergence of the lateral fields into the posterior field, the couch should be rotated in toward the collimator and degrees calculated by considering the field size and distance.
4
Q
Perforated thermoplastics are better than nonperforated thermoplastics because they:
A. reduce the average skin dose
B. increase the average skin dose
C. are much more sturdy D. make it easy to reproduce the setup
A
A. reduce the average skin dose
Rationale:
Perforated thermoplastics reduce the average skin dose compared to nonperforated thermoplastics.
5
Q
When using lateral and anterior supraclavicular fields to treat a tumor in the oropharynx, the field junction should be placed:
A. cephalad of the thyroid notch
B. caudal of the thyroid notch
C. caudal of the larynx
D. cephalad of the mandible
A
A. cephalad of the thyroid notch
Rationale:
If field matching is done while treating the oropharynx, the junction can reasonably be placed cephalad, or superior to, the thyroid notch to avoid overdosing the larynx.
6
Q
“cephalad” means what?
A
superior
7
Q
“caudad” means what?
A
inferior
8
Q
Increasing the field size from 5 x 5 to 20 x 20, with all other factors remaining the same, the percent depth dose will:
A. increase
B. decrease
C. remain the same
D. move the Dmax point
A
A. increase
Rationale:
Increasing the field size will increase the percent depth dose.
FS and PDD are directly related!!!!!
9
Q
The volume of lung within an anterior supraclavicular field can be reduced when treating breast carcinoma by:
A. elevating the arm
B. treating the supraclavicular field every other day
C. placing the angle board under the chest
D. moving the breast down on the chest wall and making the match line as superior as possible
A
D. moving the breast down on the chest wall and making the match line as superior as possible
Rationale:
To keep the volume of lung as low as possible, the match line should be as superior as possible. This may be achieved in women with larger breasts by using a position or aid that will shift the breast tissue down.
10
Q
The tolerance dose (TD 5/5) for the whole brain is:
A. 45 Gy in 25 fractions
B. 60 Gy in 30 fractions
C. 60 Gy in 15 fractions
D. 45 Gy in 15 fractions
A
A. 45 Gy in 25 fractions
Rationale:
The tolerance dose for the whole brain is 45 Gy in fractions of 1.8 to 2.0 Gy.
11
Q
Where is the depth of the 80% isodose line for 12 MeV electron beam through water?
A. 3 cm B. 4 cm C. 6 cm D. 10 cm
A
B. 4 cm
Rationale:
Use the 80% rule. 1/3 of the electron energy is the approximate depth in centimeters of the 80% isodose line.
12
Q
An excerpt from an equivalent square table shows: Using the table, the equivalent square for a field size 9.5 x 13 would be:
A. 10.6 B. 10.9 C. 11.3 D. 11.45
A
B. 10.9
Rationale:
Using interpolation between the values 10.6 and 11.3. Take the average to get 10.95.
13
Q
The closest blocked equivalent square for a 10 x 20 rectangular field with a 4 x 6 block in the field is:
A. 8.6
B. 11.4
C. 13.3
D. 15.6
A
C. 13.3
Rationale:
Subtract the area of the block from the area of the open field, and then take the square root. 10 x 20 = 200, 4 x 6 = 24. 200-24 = 176. The square root of 176 = 13.3.
14
Q
Bolus should be composed of a material:
A. having higher absorption than tissue
B. having lower absorption than tissue
C. easy to clean with disinfectant solutions
D. equivalent to tissue in absorption and scattering properties
A
D. equivalent to tissue in absorption and scattering properties
Rationale:
Bolus should be made of tissue-equivalent material.
15
Q
The dose under a 5 HVL block would be approximately:
A. 3% to 5% of the given dose
B. 5% to 10% of the given dose
C. 10% to 20% of the given dose
D. 20% to 50% of the given dose
A
A. 3% to 5% of the given dose
Rationale:
A block 5 half-value layers thick should allow about 3% of the dose applied.
16
Q
When a missing tissue compensator is used, it should be placed:
A. directly on the skin surface
B. at some distance from the skin surface
C. on the end of an electron cone
D. on top of a bolus material at isocenter
A
B. at some distance from the skin surface
Rationale:
To preserve the skin-sparing effect, tissue compensators should be placed at least 15 cm from the patient’s skin surface.
17
Q
The field size of an X-ray or gamma ray beam is defined as the area enclosed within the boundary of the __________% depth dose line.
A. 50 B. 60 C. 80 D. 100
A
A. 50
Rationale:
The 50% isodose line defines the field size of X-ray or gamma ray beams.
18
Q
When using rotational arc therapy, monitor units or treatment time should be calculated using which of the following methods?
A. Mayneord's factor B. Paterson-Parker C. tissue air ratio D. Clarkson's
A
C. tissue air ratio
Rationale:
Rotational arc treatment time/monitor units are calculated using the TAR method.
19
Q
Field gaps or abutting junctions are often shifted (feathered) a few times during the course or treatment in order to:
A. reduce the risk of nausea and vomiting
B. reduce the risk of overdosing critical structures
C. make the gap larger
D. change the exit point
A
B. reduce the risk of overdosing critical structures
Rationale:
Feathering matching junctions, or gaps, are intended to decrease the risk of overdosing or underdosing critical structures.
20
Q
Total dose to the lumpectomy site following accelerated partial breast irradiation utilizing high dose rate brachytherapy will be approximately:
A. 20 Gy B. 35 Gy C. 45 Gy D. 60 Gy
A
C. 45 Gy
Rationale:
Using APBI techniques, dose to the lumpectomy site typically ranges from 40-50 Gy
21
Q
Posterior cervical nodes need to be treated and the patient’s shoulder will only allow a treatment distance of 115 cm SSD on the 100 cm SAD linear accelerator. The inverse square factor needed in the monitor unit calculation would be:
A. (100/115)2 B. (115/100)2 C. (100/15)2 D. (15/100)2
A
A. (100/115)2
Rationale:
The inverse square factor in extended distance dose calculations is computed by the relationship: (SAD/SSD + Dmax)superscript2.
Since the energy is not specified here, Dmax can not be accounted for in this exercise.
22
Q
The attenuation of Cerrobend is less dense than lead by about:
A. 5%
B. 10%
C. 15%
D. 25%
A
C. 15%
Rationale:
Cerrobend or Lipowitz metal is about 15% less dense than lead.
23
Q
Cerrobend or Lipowitz metal is about ____% less dense than lead.
A
15%
24
Q
The tumor lethal dose of 50 cGy will need to be given to a midline abdominal tumor through a single anterior port using the SSD technique. The abdominal tumor is located at the depth of the 80% dose line, and the spinal cord is at the depth of the 75% dose line. Dose to the cord will be:
A. 66 Gy B. 50 Gy C. 47 Gy D. 37.5 Gy
A
C. 47 Gy
Rationale:
The spinal cord will receive 47 Gy.
You can compute the applied dose by using TD/%DD. 50/.80 = 62.5 Gy and then taking 75% of the applied dose- 62.5(0.75) = 47 Gy.
Or use direct proportion; 50 Gy:80% as x:75%.
25
The focus-to-film distance on a conventional simulator is 140 cm. A 5 cm wire is placed on the patient's skin. The focus-to-skin distance is 100 cm. The magnification factor is given by:
A. 100/5
B. 140/100
C. 100/140
D. 5/100
B. 140/100
Rationale:
The magnification formula is FFD/FOD = magnification. Therefore, 140/100 = 1.4.
26
A treatment designed to be given at 120 cm SSD is mistakenly given at 100 cm SSD. What is the error in dose delivered?
A. 20% overdose
B. 20% underdose
C. 44% overdose
D. 44% underdose
C. 44% overdose
Rationale:
Use the inverse square theory. The distance has changed by 20%, so the dose must change in the opposite direction by a square of the distance changed. Check your work by substituting a number for an initial intensity.
27
A dose of 55 Gy will be given through anterior and lateral ports to the maxillary sinus. The lens is included in the treatment fields. The therapeutic ratio is approximately:
A. 0.9
B. 0.18
C. 5.5
D. 11
B. 0.18
Rationale:
The tolerance dose of the lens ranges from 5 Gy to 10 Gy depending on the source. Use the upper limit of the range and the therapeutic ratio formula: 1000/5500 = 0.18.
28
The purpose of an immobilization device is to:
A. make the patient's position comfortable
B. facilitate reproducing and maintaining the position
C. prevent the patient from falling off the PSA
D. help the therapist set up the treatment faster
B. facilitate reproducing and maintaining the position
Rationale:
Immobilization devices should help in reproducing position and maintaining position.
29
Dose rates in air express the dose measured:
A. at 10 cm depth in a phantom
B. without a phantom, with a buildup cap at a certain distance
C. with a phantom, without a buildup cap at a certain distance
D. without a build up cap or phantom with a 10 x 10 cm field size
B. without a phantom, with a buildup cap at a certain distance
Rationale:
Dose rates in air are measured without a phantom and with a buildup cap to achieve electronic equilibrium at a certain distance from the source.
30
The angle between two beams is known as the :
A. arc angle
B. hinge angle
C. wedge angle
D. divergent angle
B. hinge angle
Rationale:
The degree of separation between two beams is the hinge angle.
31
If the exposure rate at 1 meter is 53.7 R/minute, at what distance is the exposure rate 35 R/minute?
A. 0.5 meters
B. 0.75 meters
C. 1.53 meters
D. 1.24 meters
D. 1.24 meters
Rationale:
Using the inverse square formula. 53.7/35 = 12 /x2, 1.53 = x2; x = 1.24.
32
Rotational arc therapy is elected for treatment to the pituitary gland. The arc is 240 degrees and the calculated monitor units are 196 MU. The MU/degree setting will be:
A. 0.817
B. 0.667
C. 1.22
D. 1.5
A. 0.817
Rationale:
To calculate the MU/degree: 196 MU/240 degrees = 0.817 MU/degree.
33
While using adjacent photon fields for treatment:
A. It doesn't mater where the hot spot occurs.
B. It doesn't matter where the cold spot occurs.
C. Dose nonuniformity due to error in abutting can be minimized by increasing the lengths every other day.
D. Dose uniformity can be improved by moving the junction or gap at regular intervals during treatment.
D. Dose uniformity can be improved by moving the junction or gap at regular intervals during treatment.
Rationale:
Adjacent photon fields should have a skin gap, and/or the junction should be feathered periodically.
34
When preparing to assist with the administration of iodine based contrast, the therapist should inspect the contrast container and use only when the content is:
A. expired
B. clear
C. viscous
D. warm
B. clear
Rationale:
Before use, contrast should be inspected and be confirmed as clear, not discolored or cloudy, and having a current date.
35
The physical size of the treatment field is defined at the interception of the central axis at the specific isocentric distance and which isodose line?
A. 10%
B. 20%
C. 50%
D. 80%
C. 50%
Rationale:
The geometric field size is defined at isocenter at the interception of the 50% isodose line.
36
A 6 MV photon beam on the linear accelerator has an output at isocenter of 1.2 cGy/MU. What is the output at an extended distance of 120 cm?
A. 0.8124
B. 0.9876
C. 1.45
D. 1.776
A. 0.8124
Rationale:
The new output can be found by multiplying the old output by the inverse square factor 0.677. Use the inverse square formula.
37
The tolerance dose (TD 5/5) for the whole lung in the adult is:
A. 1800 cGy in 5 fractions
B. 1500 cGy in 5 fractions
C. 1800 cGy in 10 fractions
D. 2400 cGy in 10 fractions
C. 1800 cGy in 10 fractions
Rationale:
The tolerance dose of the whole lung in the adult is about 17.5 Gy when standard fractionation is used:180 to 200 cGy/fraction.
38
Indian club needles have:
A. gold seed
B. one hot end
C. two hot ends
D. even activity
B. one hot end
39
The physician asks you to add a 5 x 4 corner block to a 12 x 14 open lung field. The blocked equivalent square is:
A. 7 x 7
B. 7 x 10
C. 12 x 12
D. 13 x 13
C. 12 x 12
Rationale:
To find the blocked equivalent square, subtract the blocked area from the open area. 12(14)-5(4) = 148. The square root of 148 = 12.1.
40
Diagnostic CT machines are often not suitable for therapy planning because (select two):
1. The table top is concave.
2. The bore is not large enough to accommodate various positions and devices.
3. The slice thickness cannot be varied.
4. The mode can not be switched from axial to helical.
1. The table top is concave.
2. The bore is not large enough to accommodate various positions and devices.
Rationale:
Diagnostic CT scanners do not have bores large enough to accommodate positions and positioning devices used in therapy. Although the table top is concave, the diagnostic CT table often has an insert to make the table flat.
41
An advantage to using custom compensators for missing tissue instead of bolus in megavoltage therapy is:
A. reduced penumbra
B. preservation of skin sparing
C. increased surface dose
D. increased exit dose
B. preservation of skin sparing
Rationale:
Custom compensators are placed near the collimators at a substantial distance away from the patient. This preserved the skin sparing effect of the megavoltage beam.
42
The energy loss of megavoltage (MeV) electron beams in water is approximately_____MeV/cm.
A. 10
B. 5
C. 2
D. 3
C. 2
Rationale:
Electron beams lose about 2 MeV per centimeter of tissue.
43
One disadvantage of using a vertex field to treat primary brain malignancies is that the field exits through the:
A. brain and mediastinum
B. pharynx and spinal cord
C. orbits
D. chest
B. pharynx and spinal cord
Rationale:
When treating the vertex with the patient in neutral position, the vertex field would exit through the pharynx. If the patient is treated with chin flexed, the vertex field exits through the pharynx and spinal cord.
44
A patient was to have received 250 cGy each fraction for 10 fractions at a distance of 100 cm SSD. A readout error demonstrated that the patient was actually treated at a distance of 105 cm SSD. What was the actual total dose delivered?
A. 2267 cGy
B. 2381 cGy
C. 2756 cGy
D. 2625 cGy
A. 2267 cGy
Rationale:
Use the inverse square. 2500(100/105)2 = 2267.
45
The posterior surface of the patient should be flat when treating the entire spine so that:
A. Skin gaps are smaller.
B. Dose is more uniform.
C. Position is reproducible.
D. Patients are most comfortable.
B. Dose is more uniform.
Rationale:
When treating the entire spine, the posterior surface should be as flat as possible so that dose distribution is uniform.
46
A TBI patient will be treated on a 100 cm isocentric accelerator at a distance of 450 cm. The calibrated dose rate at isocenter is 250 cGy/minute. The dose rate at the treatment distance is:
A. 55.5 cGy/minute
B. 1125 cGy/minute
C. 62.5 cGy/minute
D. 12 cGy/minute
D. 12 cGy/minute
Rationale:
Use the inverse square formula. 250(100/450)2 = 12.
47
A patient is receiving 3000 cGy total dose to a spine port using the SSD technique. The total given dose is 3636 cGy. What is the percent depth dose?
A. 100%
B. 120%
C. 82.5%
D. 75%
C. 82.5%
Rationale:
Use the applied dose formula. Given dose = TD/%DD. 3636 = 3000/x; 3000/3636 = 0.825.
48
The CTV is larger than the GTV because it includes the:
A. normal tissue
B. margins for daily uncertainties
C. areas of potential positive disease
D. lymphatic drainage
C. areas of potential positive disease
Rationale:
The CTV includes the tumor volume and areas of potentially positive disease.
49
The output of a 7 MeV electron beam, 12 x 12 cm field is 1.01 cGy/MU. Calculate the monitor units required to deliver 250 cGy to the depth of the 90% dose line.
A. 275 MU
B. 223 MU
C. 227 MU
D. none of the above
A. 275 MU
Rationale:
Use the monitor unit formula for SSD technique.
50
The ratio of dose at depth in tissue to the dose at electronic equilibrium on the beam axis is known as the:
A. tissue air ratio
B. percent depth dose
C. scatter air ratio
D. field size correction factor
B. percent depth dose
Rationale:
The percent depth dose is the ratio of dose at Dmax to dose at a certain depth in tissue.
51
ratio of dose at Dmax to dose at a certain depth in tissue = ______________
PDD
52
In order to reduce the potential for electron contamination, the preferred material for custom block and compensator holders is:
A. foil
B. Lucite
C. aluminum
D. tungsten
B. Lucite
Rationale:
Lucite is a sturdy plastic and is preferred over the other listed materials to reduce the potential for secondary, particle contamination.
53
An excerpt from an equivalent square table shows:
Using the table, the equivalent square for a field size 8 x 13.5 would be:
A. 9.3
B. 9.9
C. 10
D. 10.25
C. 10
Rationale:
Using interpolation between the values 9.9 and 10.1, the equivalent square for 8 x 13.5 would be 10 cm.
54
When treating adjacent, multiple fields on a patient:
A. Patient position should remain the same for all fields.
B. Field borders should abut on the patient's skin.
C. Fields should be treated on alternate days.
D. Patients should be positioned supine.
A. Patient position should remain the same for all fields.
Rationale:
For multiple, adjacent fields, the patient's position should remain the same to avoid hot and cold spots.
55
Calculate the equivalent square for a rectangular field 10 x 15.
A. 12 cm
B. 12.5 cm
C. 13.5 cm
D. 13 cm
A. 12 cm
Rationale:
Use Sterling's formula.
56
The clinical target volume (CTV) includes:
A. gross target and planning target volume
B. gross target and irradiation volume
C. gross target and subclinical disease
D. planning target and irradiation target volume
C. gross target and subclinical disease
Rationale:
The CTV is the gross tumor plus subclinical disease.
57
Total body irradiation must be administered with the patient at an extended distance of 450 cm SSD on our 100 cm SAD linear accelerator. The dose rate at isocenter is 250 cGy/min. The dose rate at the new treatment distance will be:
A. 12.3 cGy/min
B. 810 cGy/min
C. 55.5 cGy/min
D. 506 cGy/min
A. 12.3 cGy/min
Rationale:
The inverse square law applies. As distance changes, the dose rate (intensity) changes inversely, by a square of the distance.
58
Which of the following radioisotopes is sometimes administered into the peritoneal cavity in the treatment of gynecological malignancies?
A. Cesium-137
B. Iridium-192
C. Iodine-131
D. Phosphorus-32
D. Phosphorus-32
Rationale:
Phosphorus-32 can be suspended in liquid and administered intracavitarily for the management of gynecologic malignancies that have spread to the abdominal cavity.
59
Rotational arc therapy is elected for treatment to the pituitary gland. The arc is 240 degrees and the calculated monitor units are 196 MU. The MU/degree setting will be:
A. 0.817
B. 0.667
C. 1.22
D. 1.5
A. 0.817
Rationale:
To calculate the MU/degree: 196 MU/240 degrees = 0.817 MU/degree.
60
Adjacent fields with respective lengths of 40 cm and 36 cm should intersect at a depth of 10 cm. The patient will be treated on a 100 cm isocentric accelerator using the SSD technique. Calculate the skin gap.
A. 4.4 cm
B. 3.4 cm
C. 3.8 cm
D. 2.2 cm
C. 3.8 cm
Rationale:
Gap formula is L/2 (d/SSD) for field one + L/2 (d/SSD) for field two.
61
A good surface landmark to approximate the apex of the lung is the:
A. clavicle
B. sternal angle
C. thyroid notch
D. cricoid notch
A. clavicle
Rationale:
The apex of the lung is approximately 3 cm superior to the clavicle.
62
The linear accelerator dose rate is 250 MU/minute. What will be the treatment time for a treatment field receiving 100 MU?
A. 0.4 seconds
B. 2.5 seconds
C. 4.0 seconds
D. 24 seconds
D. 24 seconds
Rationale:
At 250 MU/minute. Using a direct proportion, it will take 0.4 minutes to deliver 100 MU. Convert the 0.4 minutes to 24 seconds also using direct proportion.
63
Assuming ideal patient contour, two fields utilizing 30 degree wedges have an optimal hinge angle of:
A. 20 degrees
B. 180 degrees
C. 120 degrees
D. 60 degrees
C. 120 degrees
Rationale:
Use the hinge angle formula.
64
A tumor that can be completely eradicated by radiation is known to be:
A. radioresistant
B. radiocurable
C. reoxygenated
D. recurrent
B. radiocurable
Rationale:
A tumor that can be completely eradicated by radiation is called radiocurable.
65
Surface mold brachytherapy is appropriate for all of the following except:
A. pelvic sidewall tumors
B. hard palate tumors
C. orbit tumors
D. superficial skin cancer
A. pelvic sidewall tumors
Rationale:
Mold therapy is appropriate in superficially located tumors in the oral cavity, skin, or eye.
66
The 50% isodose line for a 12 MeV electron beam would be at an approximate depth of:
A. 3 cm
B. 4 cm
C. 5 cm
D. 6 cm
C. 5 cm
Rationale:
Use the rules for electron beam therapy: 4(E) = depth of 50% isodose in millimeters. 4(12) = 48 mm or E = 2.5 x depth of 50% isodose in centimeters. 12 = 2.5(x).
67
Percent depth dose varies with:
1. depth
2. fractionation
3. field size
4. radiation quality
A. 1, 3
B. 2, 4
C. 1, 3, 4
D. 1, 2, 3, 4
C. 1, 3, 4
Rationale:
Percent depth dose varies with the depth in tissue, the field size, and beam energy.
68
Kidney tolerance (TD 5/5) in the adult would be:
A. 2000 cGy delivered in 5 fractions
B. 1500 cGy delivered in 5 fractions
C. 2000 cGy delivered in 10 fractions
D. 2400 cGy delivered in 10 fractions
C. 2000 cGy delivered in 10 fractions
Rationale:
The tolerance dose of the kidney in the adult is about 1800 to 2300 cGy using standard fractionation of 180 to 200 each fraction.
69
Calculate the monitor units necessary to deliver 150 cGy to a depth of 5 cm using a single field SAD technique. The reference dose rate is 0.998 cGy/MU. The field size factor is 1.02 and the TAR is .856.
A. 172 MU
B. 147 MU
C. 176 MU
D. 182 MU
A. 172 MU
Rationale:
Use the monitor unit formula. TD/dose rate x field size factor x TAR.
70
Radiation therapy to treat medullary thyroid cancer requires large treatment portals that include:
1. the lesion
2. bilateral supraclavicular nodes
3. superior mediastinum
A. 1, 2
B. 1, 3
C. 2, 3
D. 1, 2, 3
D. 1, 2, 3
Rationale:
If medullary thyroid cancer is treated with radiation, the field will include the lesion, bilateral supraclavicular nodes, and superior mediastinal nodes.
71
Because electrons scatter so readily in the air, they are:
A. removed before striking the target
B. focused by cones extending close to isocenter
C. bent by 90 or 270 degrees toward the collimator
D. used only at distances shorter than the SAD
B. focused by cones extending close to isocenter
Rationale:
Cones are used to help keep electrons focused due to their potential to scatter in air.
72
In the usual orientation of the three planes with respect to the patient:
A. The transverse plane lies across the patient.
B. The sagittal plane lies across the patient.
C. The coronal plane lies parallel with the x axis.
D. The sagittal plane lies parallel with the z axis.
A. The transverse plane lies across the patient.
Rationale:
The transverse plane corresponds to the axial plane and lies across the patient, dividing the patient into upper and lower halves
73
Using a 100 cm SAD machine, an anterior SSD reading of 86.5 cm, and posterior SSD reading of 85.5 cm are given. The total anterior to posterior separation along the central axis is:
A. 14.5 cm
B. 24 cm
C. 28 cm
D. 14 cm
C. 28 cm
Rationale:
The separation can be found by adding the depths of isocenter in parallel opposed fields. 13.5 + 14.5 = 28.
74
Hypogastric lymph nodes would likely be included in radiation field for the treatment of the:
A. base of tongue
B. stomach
C. esophagus
D. rectum
D. rectum
Rationale:
The hypogastric lymph nodes are part of external iliac chain of nodes in the pelvis and would likely be included in fields for rectal carcinoma.
75
An entire spine needs treatment with field dimensions of 9 x 45. The 100 cm SAD linear accelerator to be used has a collimator limit of 40 x 40. What treatment distance will be required?
A. 89 cm SSD
B. 140 cm SSD
C. 105 cm SSD
D. 112.5 cm SSD
D. 112.5 cm SSD
Rationale:
Using direct proportion. Take the largest dimension needed. 4:100 as 45:x. 40(x) = 45(100). X = 112.5.
76
The dose rate on a linear accelerator is 200 MU/minute. How long is a treatment requiring 240 MU?
A. 0.694 minutes
B. 0.833 minutes
C. 1.2 minutes
D. 1.44 minutes
C. 1.2 minutes
77
Wedge angle refers to:
A. the angle of the actual wedge filter
B. the angle at which an isodose curve at a specific depth is tilted as a result of the wedge being inserted in the beam
C. the angle at which an isodose curve at a specified depth is tilted with respect to the central axis of the beam
B. the angle at which an isodose curve at a specific depth is tilted as a result of the wedge being inserted in the beam
Rationale:
The tilt of the isodose curve at a specified depth when a wedge filter is inserted is how the wedge angle is specified.
78
If the output of a machine is 130 rad/min at 80 cm, what is the output at 60 cm?
A. 65 rad/min
B. 231 rad/min
C. 110 rad/min
D. 150 rad/min
B. 231 rad/min
Rationale:
Use the inverse square. 130 (80/60)2 = 231.
79
Assuming ideal patient contour, a suitable wedge angle for two fields separated by 90 degrees would be:
A. 30 degrees
B. 45 degrees
C. 60 degrees
D. 90 degrees
B. 45 degrees
Rationale:
Use the hinge angle formula. Hinge = 180 - 2(w). 90 = 180 - 2(x).
80
An entire spine is treated by matching two fields both treated at 100 cm SSD. Field number 1 measures 8 x 20 and field number 2 measures 8 x 25. In order to match these fields at a depth of 5 cm, a_______cm skin gap would be required.
A. 1.1 cm
B. 2.0 cm
C. 5.0 cm
D. 3.2 cm
A. 1.1 cm
Rationale:
Use the gap formula. L/2(d/SSD) + L/2 (d/SSD) = skin gap
20/2 (5/100) + 25/2 (5/100) = 1.1 cm.
81
What is the equivalent square for a 15 x 6 field?
A. 9.5 x 9.5
B. 8.6 x 8.6
C. 10 x 10
D. 2.1 x 2.1
B. 8.6 x 8.6
Rationale:
Use Sterling's formula. 2(w x L)/ w + L. 2(15 x 6)/ 15 + 6 = 8.6.
82
A TBI patient will be treated on a 100 cm isocentric accelerator at a distance of 450 cm. The calibrated dose rate at isocenter is 250 cGy/minute. The dose rate at the treatment distance is:
A. 55.5 cGy/minute
B. 1125 cGy/minute
C. 62.5 cGy/minute
D. 12 cGy/minute
D. 12 cGy/minute
Rationale:
Use the inverse square formula. 250(100/450)2 = 12.
83
A patient is treated using the SAD technique on a 100 cm isocentric linear accelerator. The field size is 24 x 20. The isocenter is located 5 cm below the patient's skin surface. What does the field measure on the patient's skin?
A. 24 x 20
B. 19 x 15
C. 23 x 19
D. 22 x 22
C. 23 x 19
Rationale:
Use direct proportion.
84
Custom tissue compensators are used to:
A. filter scattered electrons
B. reduce the beam energy
C. compensate for surface irregularity
D. none of the above
C. compensate for surface irregularity
Rationale:
Custom compensators compensate for surface irregularities.
85
In the maintenance phase of managing ALL, whole brain irradiation may be given with the inferior border of the treatment field at the:
A. base of skull
B. mastoid tip
C. cervical spine #2
D. cervical spine #7
C. cervical spine #2
Rationale:
In the maintenance phase of ALL, whole brain irradiation may be administered using the helmet technique where the inferior border is at C2.
86
An advantage of using the wedged pair technique is that beyond the point of beam intersection, there is:
A. rapid dose buildup
B. rapid dose falloff
C. isodose uniformity
D. heel-effect dose
B. rapid dose falloff
Rationale:
When using the wedged pair, the highest dose concentration is near the hinge, and then there is rapid dose falloff beyond the hinge.
87
A patient is receiving 3000 cGy total dose to a spine port using the SSD technique. The total given dose is 3636 cGy. What is the percent depth dose?
A. 100%
B. 120%
C. 82.5%
D. 75%
C. 82.5%
Rationale:
Use the applied dose formula. Given dose = TD/%DD. 3636 = 3000/x; 3000/3636 = 0.825.
88
Monitoring setup reproducibility:
A. is usually accomplished by weekly port films
B. is always accomplished by using electronic portal imaging
C. can be accomplished by visual comparison of simulation films/DRRs and port films, or by electronic portal imaging
D. is not necessary in most patients
C. can be accomplished by visual comparison of simulation films/DRRs and port films, or by electronic portal imaging
Rationale:
Periodic comparison of treatment verification ports to DRRs or conventional simulation films is a means to monitor setup reproducibility.
89
The isodose chart shown is for an electron beam energy of approximately:
A. 5 MeV
B. 7 MeV
C. 9 MeV
D. 12 MeV
C. 9 MeV
Rationale:
Using the rules for electron energy and isodose depths, you can apply the 80% rule: E/3 = 3 cm (depth of the 80% dose line).
90
What thickness of cerrobend would be equivalent to 5 cm of lead?
A. 4.2
B. 5
C. 6
D. 7.2
C. 6
Rationale:
Cerrobend is about 15% less dense than lead. To figure the equivalent attenuation of cerrobend to lead, use the factor 1.2. 1 cm lead = 1.2 cm cerrobend.
91
Bone metastasis to the thoracic spine is often managed using________treatment field(s).
A. parallel opposed
B. 90 degree hinged
C. single posterior
D. IMRT
C. single posterior
Rationale:
The thoracic spine is usually treated using a posterior port since the thoracic spine is located near the posterior surface.
92
The _____% isodose line defines the field size of X-ray or gamma ray beams.
50
93
A treatment designed to be given at 120 cm SSD is mistakenly given at 100 cm SSD. What is the error in dose delivered?
A. 20% overdose
B. 20% underdose
C. 44% overdose
D. 44% underdose
C. 44% overdose
Rationale:
Use the inverse square theory. The distance has changed by 20%, so the dose must change in the opposite direction by a square of the distance changed. Check your work by substituting a number for an initial intensity.
94
Digitally reconstructed radiographs (DRRs) can be generated from:
A. conventional simulation fluoroscopic images
B. ultrasound images
C. conventional X-ray images
D. CT images
D. CT images
Rationale:
DRRs are generated from CT images.
95
The depth of the 80% dose line for a clinical electron beam energy is given by:
A. 1/4 of the energy
B. 1/3 of the energy
C. 1/2 of the energy
D. 1/10 of the energy
B. 1/3 of the energy
Rationale:
The depth of the 80% dose line is found by dividing the energy by 3.
96
The factors that determine the number of treatment fields to be used includes:
1. beam quality
2. adjacent normal tissue
3. tumor depth
4. tumor shape
A. 1, 3
B. 1, 4
C. 1, 2, 3
D. 1, 2, 3, 4
D. 1, 2, 3, 4
Rationale:
The number of treatment fields to be used depends on the depth of the tumor, adjacent tissue, shape of the tumor and beam quality.
97
If a patient is to be treated at 140 cm SSD on a linear accelerator and the treatment field size is 22 x 40 at this extended distance, what would be the required collimator setting?
A. 22 x 40
B. 16 x 29
C. 11 x 20
D. 8 x 16
B. 16 x 29
Rationale:
Use direct proportion: 22:140 as x:100. Use this for both dimensions. The collimator setting is the measured field size at isocenter.
98
In order to make custom Cerrobend blocks, the following information is needed:
1. target-to-film distance
2. beam energy
3. patient thickness
A. 1, 2
B. 2, 3
C. 1, 3
D. 1, 2, 3
A. 1, 2
Rationale:
In order to make custom blocks, the cutter must know the energy of the machine, the target-to-film distance, and the target-to-tray distance.
99
The use of special blocks or multileaf collimators to create a treatment beam area of proportions other than those capable of the primary collimator system is known as:
A. beam shaping
B. beam spoiling
C. beam shifting
D. beam flattening
A. beam shaping
Rationale:
Beam shaping is accomplished with customized blocks or collimators.
100
The average life of a radioactive source with a half-life of 32 minutes is:
A. 64 minutes
B. 320 minutes
C. 46 minutes
D. 96 minutes
C. 46 minutes
Rationale:
Use the average life formula. Ta = 1.44(half-life).
101
The collimator setting on a 100 cm SAD linear accelerator is 10 x 20. When treating a patient at 120 cm SSD, what does this field measure on the patient's skin?
A. 8.3 x 16.7
B. 12 x 24
C. 10 x 20
D. 20 x 40
B. 12 x 24
Rationale:
Field size and distance have a direct relationship. Direct proportion can be used here. As distance increases, field size increases.
102
The Dmax for a 6 MV photon beam is approximately:
A. 1 cm
B. 1.5 cm
C. 2 cm
D. 2.5 cm
B. 1.5 cm
Rationale:
The point of electronic equilibrium for a 6 MV photon beam is 1.5 cm.
103
Increasing the distance from 80 cm to 90 cm causes the dose rate to change by:
A. 0.888
B. 0.79
C. 1.125
D. 1.265
B. 0.79
Rationale:
Increasing the distance from 80 to 90 will change the dose rate by a factor of 0.790. Use the inverse square factor (80/90)*superscript*2.
104
Radiation therapy using a solid or sealed radioisotope for the body surface or tissue implantation is:
A. brachytherapy
B. total body irradiation
C. large field irradiation
D. cobalt therapy
A. brachytherapy
105
When treating an extremity, the limb should be positioned:
A. parallel to the horizontal axis of the beam
B. perpendicular to the table
C. resting on a sponge
D. parallel to the torso
A. parallel to the horizontal axis of the beam
Rationale:
For dose homogeneity, limbs should be positioned parallel to the table or to the horizontal axis of the beam.
106
During verification placement imaging for radioactive needles, the image receptor is located 120 cm from the source. The 3-inch needles measure 4.0 cm on the film. How far away were the needles from the image receptor?
A. 130 cm
B. 120 cm
C. 90 cm
D. 30 cm
D. 30 cm
Rationale:
Using direct proportion and magnification rules: 4/3 = magnification and 120/SAD = magnification. By substitution 4/3 = 120/SAD. SAD = 90 cm therefore, the needles had to be 30 cm from the image receptor. Draw a diagram to visualize.
107
If the cGy/MU is 1.0 at 100 cm SSD, what is the cGy/MU at 200 cm SSD?
A. 0.25 cGy/MU
B. 2.0 cGy/MU
C. 0.5 cGy/MU
D. 4.0 cGy/MU
A. 0.25 cGy/MU
Rationale:
Use the inverse square formula.
108
Treating a patient with a 4 MV photon beam delivers maximum dose below the skin surface at a depth of:
A. 0.5 cm
B. 1.0 cm
C. 1.5 cm
D. 2.0 cm
B. 1.0 cm
Rationale:
Dmax dose for a 4 MV beam is at 1.0 cm below the skin surface.
109
When comparing an isodose profile from a linear accelerator with one from an orthovoltage machine, the linear accelerator isodose will have the following characteristics:
1. greater penetration
2. greater side scatter
3. higher % DD at depth
4. flatter isodose lines
A. 1, 2, 3
B. 2, 3, 4
C. 1, 3, 4
D. 1, 2
C. 1, 3, 4
Rationale:
The linear accelerator beam will be of greater energy so it will show greater penetration, less side scatter, higher percent depth dose and flatter isodose lines.
110
A dose of 300 cGy was to be delivered to the thoracic spine at 95 cm SSD. An error caused treatment to be given at an SSD of 92 cm. The actual dose delivered was:
A. 281
B. 291
C. 320
D. 341
C. 320
Rationale:
The inverse square law applies here. 300(95/92)2 = 320.
111
When treating the maxillary antrum, the organ at the greatest risk for damage is the:
A. pituitary
B. brain
C. lens
D. sphenoid
C. lens
Rationale:
The floor of the orbit is the superior edge of the maxillary sinus. Treatment fields are in close proximity to the radiosensitive lens.
112
A source of I-131 has an activity of 2.5 mCi. What is the activity after 12 days?
A. 0.9 mCi
B. 30 mCi
C. 0.21 mCi
D. 2.5 mCi
A. 0.9 mCi
Rationale:
Recall that the half-life of iodine 131 is 8 days. Use the activity formula.
113
A patient treated with two fields separated by 120 degrees, likely needs a ________degree wedge inserted for even dose distribution.
A. 30
B. 45
C. 60
D. 15
A. 30
Rationale:
Use the hinge angle formula.
114
The best position for treating the vertex field is:
A. chin extended as much as possible
B. chin flexed
C. chin turned to one side
D. chin extension at 12 cm
B. chin flexed
Rationale:
The vertex is best treated with the chin flexed. This position makes the field easy to image.
115
Applying a radioactive material inside or in close proximity to the patient is known as:
A. external beam radiation therapy
B. proton beam radiation therapy
C. tomotherapy
D. brachytherapy
D. brachytherapy
116
The tolerance dose (TD 5/5) for the whole brain is:
A. 45 Gy in 25 fractions
B. 60 Gy in 30 fractions
C. 60 Gy in 15 fractions
D. 45 Gy in 15 fractions
A. 45 Gy in 25 fractions
Rationale:
The tolerance dose for the whole brain is 45 Gy in fractions of 1.8 to 2.0 Gy.
117
The use of the wedge filter helps to:
1. achieve a more homogenous dose distribution
2. compensate for the absence or presence of tissue
3. avoid hot spots
A. 3
B. 2
C. 1, 2, 3
D. 2, 3
C. 1, 2, 3
Rationale:
The wedge compensates for the absence or presence of tissue to achieve more homogenous dose distribution and avoid hot and cold spots.
118
The width of penumbra increases with increasing:
A. SSD
B. source to collimator distance
C. energy
D. SAD
A. SSD
Rationale:
Penumbra increases with increasing SSD and source size.
119
If a tumor receives 225 cGy at a point where the percent depth dose is 75%, the dose at maximum buildup is:
A. 150 cGy
B. 170 cGy
C. 250 cGy
D. 300 cGy
D. 300 cGy
Rationale:
Using the applied dose formula. Applied dose = TD/%DD. 225/75% = 300.
120
Calculate the magnification factor for an object measuring 6 cm on a film. The SOD was 70 cm and the SFD was 100 cm.
A. 1.43
B. 0.7
C. 0.08
D. 4.6
A. 1.43
Rationale:
Use magnification formula. SFD/SOD = magnification.
121
A patient is treated on a linear accelerator. The treatment distance is 94 cm SSD. The TAR at the treatment depth is 0.888 and the output is 1.02 cGy/monitor unit. How many monitor units are required to deliver 100 cGy?
A. 98 MU
B. 110 MU
C. 113 MU
D. 100 MU
B. 110 MU
Rationale:
Use the monitor unit formula. TD/output x TAR. Use the factors given.
122
For patients with bladder cancer, the preoperative radiation treatment fields should be large enough to include the bladder and regional nodes such as:
A. obturator and inguinal
B. obturator, external iliac, and internal iliac
C. hypogastric and external iliac
D. external iliac, hypogastric, and inguinal
B. obturator, external iliac, and internal iliac
Rationale:
Treatment fields for bladder carcinoma should include the tumor volume, external and internal iliacs, and obturator lymph nodes.
123
Which of the following formulas represents the activity formula?
A. A = mc*superscript*2
B. *superscript* A = Aoe^(λ)(t)
C. A = A/ λ
D. T 1/2 = 1/ λ
B. *superscript* A = Aoe^(λ)(t)
Rationale:
The activity formula should has an ending activity (A) and original activity (A0). The formula should show the relationship between activity and decay constant and the elapsing of time.
124
Treatment planning involves selection of:
1. daily dose
2. beam arrangement
3. fractionation
4. tumor dose
A. 2, 3
B. 1, 4
C. 2, 3, 4
D. 1, 2, 3, 4
D. 1, 2, 3, 4
Rationale:
Treatment planning involves prescription of dose and fractionation and beam arrangement.
125
A 6 MV photon beam on the linear accelerator has an output at isocenter of 1.2 cGy/MU. What is the output at an extended distance of 120 cm?
A. 0.8124
B. 0.9876
C. 1.45
D. 1.776
A. 0.8124
Rationale:
The new output can be found by multiplying the old output by the inverse square factor 0.677. Use the inverse square formula.
126
A large area must be treated measuring 45 x 60 cm. On a 100 cm SAD linac with a limited collimator setting of 40 x 40, a distance of ______ would be required to accommodate this field size.
A. 145 cm
B. 160 cm
C. 95 cm
D. 150 cm
D. 150 cm
Rationale:
Field size and distance have a direct relationship. Direct proportion can be used here. Since one field dimension is larger than the other, the largest field dimension required should be used in the direct proportion formula
127
The expected total dose to point A for treatment of the cervix from both external radiation and brachytherapy is approximately:
A. 35 Gy
B. 70 Gy
C. 90 Gy
D. 140 Gy
C. 90 Gy
Rationale:
A patient with bulky disease can receive 40 to 45 Gy with external beam and an additional 40 to 50 Gy with low-dose or high-high dose brachytherapy.
128
A fixed point in air around which the treatment machine rotates is called the:
A. isocenter
B. surface dose
C. isodose curve
D. gantry
A. isocenter
Rationale:
The isocenter is a fixed point in air around which the gantry, collimator, and table rotate.
129
A wedge transmission factor of 0.895 indicates a wedge attenuation of the beam by:
A. 89.5%
B. 10.5%
C. 100%
D. 3% to 5%
B. 10.5%
Rationale:
The transmission factor indicates the percent of beam coming through. 100%-89.5% = 10.5% (attenuated).
130
All thermoplastic materials need some kind of base plate support on the couch top. It is preferable to have these plates made of:
A. high-density material
B. nontissue equivalent material
C. carbon fiber material
D. Lucite
C. carbon fiber material
Rationale:
The base plate support for thermoplastic immobilization devices should preferably be made of carbon fiber due to its low attenuation.
131
The dose under a 5 HVL block would be approximately:
A. 3% to 5% of the given dose
B. 5% to 10% of the given dose
C. 10% to 20% of the given dose
D. 20% to 50% of the given dose
A. 3% to 5% of the given dose
Rationale:
A block 5 half-value layers thick should allow about 3% of the dose applied.
132
The equivalent square field size must be determined in order to calculate the:
A. dose to be delivered to the central axis of an irregular field
B. relative dose values from a reference beam
C. spread of the beam from a certain distance from the target
D. air gap on the patient's external contour
A. dose to be delivered to the central axis of an irregular field
Rationale:
The equivalent square is necessary to calculate the dose to be delivered to the central axis of a nonsquare field.
133
***As SSD increases, depth dose:***
A. does not change
B. increases
C. decreases
***B. increases***
Rationale:
The dose at depth increases as the source to skin distances increases.
134
Overall, most intracranial malignancies are:
A. glioblastoma multiforme
B. astrocytoma
C. metastatic
D. pituitary adenoma
C. metastatic
Rationale:
Overall, the majority of intracranial malignancies are metastatic.
135
The percent depth dose is 91.8% for a 10 MV beam with a field size of 12 x 12 at 5 cm depth and 80 cm SSD. Calculate the percent depth dose for the same field size and depth for 100 cm SSD.
A. 81.5
B. 83.8
C. 87.4
D. 92.9
D. 92.9
Rationale:
Use Mayneord's formula. Use the F factor then multiply by the old percent depth dose.
136
What is the range in soft tissue of a 12 MeV electron beam?
A. 3 cm
B. 4 cm
C. 6 cm
D. 10 cm
C. 6 cm
Rationale:
The range, in centimeters, of an electron beam in tissue/water is 1/2 of the beam energy.
137
The tumor lethal dose of 50 cGy will need to be given to a midline abdominal tumor through a single anterior port using the SSD technique. The abdominal tumor is located at the depth of the 80% dose line, and the spinal cord is at the depth of the 75% dose line. Dose to the cord will be:
A. 66 Gy
B. 50 Gy
C. 47 Gy
D. 37.5 Gy
C. 47 Gy
Rationale:
The spinal cord will receive 47 Gy. You can compute the applied dose by using TD/%DD. 50/.80 = 62.5 Gy and then taking 75% of the applied dose- 62.5(0.75) = 47 Gy. Or use direct proportion; 50 Gy:80% as x:75%.
138
The physician asks you to add a 4 x 4 cm corner block to a 15 x 15 cm open lung field. The blocked equivalent square is:
A. 11 x 11
B. 14.4 x 14.4
C. 19 x 19
D. 12.6 x 12.6
B. 14.4 x 14.4
Rationale:
To find the blocked equivalent square, subtract the blocked area from the open area. 15(15) - 4(4) = 209. The square root of 209 = 14.4
139
What would be the finishing angle for a clockwise rotational arc starting at 280 degrees with an MU setting of 205 and MU/degree of 1.21?
A. 94 degrees
B. 101 degrees
C. 89 degrees
D. 132 degrees
C. 89 degrees
Rationale:
Draw the gantry dial. Compute the number of degrees rotated when administering 205 MU. 205/1.21 Mu/dgree = 169 degrees. Then, count degrees from the starting angle.
140
The maximum, acceptable amount of dose transmitted through the multileaf collimators is:
A. 1%
B. 5%
C. 10%
D. 15%
B. 5%
Rationale:
The acceptable amount of transmission through the MLC, or fabricated blocks, is 5%.
141
Anatomical data for CT imaging and reconstruction is acquired through the:
A. coronal plane
B. transverse plane
C. sagittal plane
D. none of the above
B. transverse plane
Rationale:
Anatomical data is acquired through the transverse plane during scanning.
142
What type of image would yield the poorest contrast quality when visualizing soft tissue?
A. CT image
B. MRI image
C. mega-voltage portal image
D. diagnostic X-ray image
C. mega-voltage portal image
Rationale:
Mega-voltage photons are highly penetrating, so there is little tissue absorption on a portal image compared to a CT or diagnostic X-ray image.
143
The actual physical dimensions of the tumor, including regions of presumed occult spread, is the:
A. absorbed dose volume
B. irradiation volume
C. treatment volume
D. tumor volume
D. tumor volume
Rationale:
The tumor volume shows the physical dimensions of the tumor, including regions of presumed spread.
144
Opposed tangential fields would likely be used in the treatment of the:
A. breast
B. spleen
C. femur
D. esophagus
A. breast
Rationale:
Opposing tangential fields are used in the treatment of the breast.
145
Which of the following therapeutic ratios would be expected to provide the highest probability of cure?
A. 0.85
B. 1
C. 1.45
D. 1.75
D. 1.75
Rationale:
The highest probability of cure is expected with the highest therapeutic ratio. Normal tissue tolerance/tumor lethal dose = therapeutic ratio.
146
When performing manual contouring, it is important to:
A. contour the patient in treatment position
B. verify the beam energy to be used.
C. establish the beam arrangement planned
D. all of the above
A. contour the patient in treatment position
Rationale:
When contouring, patient data must be acquired while the patient is in the treatment position. It is not necessary to know energy and beam arrangement at the time of contouring. However, the therapist should acquire contour data in every possible aspect of anatomy that might be encountered by the beam after planning.
147
The half-life of I-125 is 60 days. In 6 months, the activity of the source will be ____ of the original.
148
The half-life of I-125 is 60 days. In 6 months, the activity of the source will be ____ of the original.
A. 70%
B. 50%
C. 1/8
D. 5%
E. 1/64
C. 1/8
Rationale:
Follow the principle of half-lives. One half-life is 60 days. There are 3 half-lives in 6 months. Three half-lives decrease activity to 1/8 of the original.
149
In preparation for Fletcher's suite brachytherapy, an orthogonal set of films was acquired on the conventional simulator. The hinge angle for the set of films was:
A. 45 degrees
B. 90 degrees
C. 180 degrees
D. not enough information given
B. 90 degrees
Rationale:
An orthogonal set of films are films taken 90 degrees apart.
150
With all other factors remaining the same, increasing the field size from 6 x 6 to 10 x 10, backscatter would:
A. increase
B. decrease
C. remain the same
D. fall away
A. increase
Rationale:
Increasing the field size increases the backscatter.
151
A device used to measure patient diameter and body thickness is called a:
A. wedge
B. compensator
C. bolus
D. caliper
D. caliper
152
The ratio of dose at depth in tissue to the dose at electronic equilibrium on the beam axis is known as the:
A. tissue air ratio
B. percent depth dose
C. scatter air ratio
D. field size correction factor
B. percent depth dose
Rationale:
The percent depth dose is the ratio of dose at Dmax to dose at a certain depth in tissue.
153
An advantage to using custom compensators for missing tissue instead of bolus in megavoltage therapy is:
A. reduced penumbra
B. preservation of skin sparing
C. increased surface dose
D. increased exit dose
B. preservation of skin sparing
Rationale:
Custom compensators are placed near the collimators at a substantial distance away from the patient. This preserved the skin sparing effect of the megavoltage beam.
154
Target volume delineation for lung tumors may involve cardiac or respiratory gating procedures. The rationale for this is that lung tumors:
A. often metastasize
B. are difficult to image
C. move with cardiac and respiratory motion
D. change shape with cardiac and respiratory motion
C. move with cardiac and respiratory motion
Rationale:
Due to cardiac and respiratory motion, lung tumors move as the heart beats and also on inspiration and expiration. To decrease the risk of target miss, cardiac or respiratory gating procedures may be utilized.
155
What is the dose at Dmax for a patient receiving 200 cGy to a depth of 3 cm where the percent depth dose is 97%?
A. 206 cGy
B. 394 cGy
C. 400 cGy
D. 300 cGy
A. 206 cGy
Rationale:
Use the applied dose formula. 200/97% = 206.
156
One disadvantage of using a vertex field to treat primary brain malignancies is that the field exits through the:
A. brain and mediastinum
B. pharynx and spinal cord
C. orbits
D. chest
B. pharynx and spinal cord
Rationale:
When treating the vertex with the patient in neutral position, the vertex field would exit through the pharynx.
If the patient is treated with chin flexed, the vertex field exits through the pharynx and spinal cord.
157
The range in water of a 20 MeV electron beam is approximately:
A. 10 cm
B. 3.33 cm
C. 5 cm
D. 2 cm
A. 10 cm
Rationale:
The range of an electron beam is found by dividing the energy by 2.
158
When treating the whole brain with opposing laterals, one way to minimize beam divergence into the eye opposite the entrance port would be to:
A. rotate the collimator
B. center the axis near the lateral canthus
C. turn the patient's head slightly away from the beam
D. rotate the couch away from the gantry
B. center the axis near the lateral canthus
Rationale:
Since there is no beam divergence at the central axis, placing the central axis near the lateral canthus and then using beam shaping would minimize beam divergence to the opposite eye.
159
Which radioisotope is commonly used for permanent, interstitial implants of the prostate gland?
A. Cesium-137
B. Cobalt-60
C. Gold-198
D. Iodine-131
C. Gold-198
Rationale:
Gold-198, Iodine-125, or Palladium-103 seeds are commonly used for permanent prostate implants.
160
A magnification ring measures 5.0 cm on a simulation film. The actual size of the ring is 3.0 cm. The ring is located 85 cm from the target. What is the target to film distance?
A. 85 cm
B. 100 cm
C. 142 cm
D. 167 cm
C. 142 cm
Rationale:
Use the magnification formula. Image size/object size = mag factor and target to film distance/target to object distance = mag factor. 5/3 = 1.67; x/85 = 1.67; 85(1.67) = 142 cm.
161
The term used to define the area on the surface of the patient on which radiation is incident is the:
A. irradiated volume
B. central axis
C. target volume
D. entrance point
D. entrance point
Rationale:
The entrance point is the area on the surface of the patient on which radiation is incident.
162
A volume that consists of the demonstrated tumor and any other tissue presumed to contain tumor is called the:
A. integral volume
B. treatment volume
C. target volume
D. irradiated volume
C. target volume
Rationale:
The tumor and any other tissue presumed to contain tumor is the target volume.
163
The shape of the isodose curves depends largely upon:
1. field size
2. depth dose
3. flattening filters
4. SSD
A. 1, 4
B. 1, 3
C. 2, 4
D. 2, 3
B. 1, 3
Rationale:
The shape of the isodose curve depends on the field size, filters and accessories such as blocks, wedges, cones and multi-leaf collimators.
164
Tissue inhomogeneites that may alter dose distribution would include:
1. air cavities
2. lung
3. fat
4. bone
A. 1, 2
B. 3, 4
C. 1, 3, 4
D. 1, 2, 3, 4
D. 1, 2, 3, 4
Rationale:
During treatment planning, any tissues without the same density as water may alter dose distribution.
165
The dose rate used for low dose rate (LDR) brachytherapy procedures is typically:
A. 20 Gy/minute
B. 10 Gy/minute
C. 2 Gy/minute
D. 0.05 Gy/minute
C. 2 Gy/minute
Rationale:
The normal range for LDR brachytherapy is 0.5 to 2.0 Gy/minute.
166
A dose of 4500 cGy is delivered at a depth of 10 cm where the percent depth dose is 62%. What is the dose to an organ anterior to the target where the percent depth dose is 72%?
A. 4950 cGy
B. 4050 cGy
C. 5226 cGy
D. 5676 cGy
C. 5226 cGy
Rationale:
You may use direct proportion or solve for the applied dose and multiply by 72%. 4500/62% = 7258. 7258(72%) = 5226.
167
For patients with pancreatic cancer, extra care is taken to limit dose to the radiosensitive:
A. heart, stomach, and small bowel
B. stomach, kidney, and small bowel
C. stomach, rectum, and bladder
D. liver, kidney, and spinal cord
D. liver, kidney, and spinal cord
Rationale:
Beam arrangement and field shaping should keep doses low to the low tolerance liver and kidneys and spinal cord during radiation to the pancreas.
168
An 8 MeV electron beam is used to deliver 300 cGy to the 90% isodose line. The cone size is 15 x 15 and the SSD is 100 cm SSD. The cone factor is .872 for the specified cone, and the reference dose rate is 1.0 cGy/MU. What MU setting should be used to deliver this treatment?
A. 344 MU
B. 300 MU
C. 382 MU
D. 333 MU
C. 382 MU
Rationale:
Use the monitor unit formula for SSD technique. TD/cone factor x dose rate x %DD.
169
What type of tissue will appear darkest on a CT image?
A. bone
B. water
C. muscle
D. lung
D. lung
Rationale:
Lung tissue has the lowest density compared to the other tissues, so it will absorb the least amount of radiation, resulting in the appearance of a darker image.
170
A left-sided brain lesion is to receive 3000 cGy using parallel opposed lateral fields with 1.5:1.0 (left: right) weighting. The total dose delivered to the left lateral field will be:
A. 1800 cGy
B. 4500 cGy
C. 1200 cGy
D. 2000 cGy
A. 1800 cGy
Rationale:
For unequally weighted fields, add the weights: 1.5+1 = 2.5. Then divide the total dose by the total weights to figure one portion: 3000/2.5 = 1200. The left lateral receives 1.5 portions: 1200 (1.5) = 1800
171
The dose at the point where the axis of the beam emerges from the patient is known as the:
A. entrance dose
B. exit dose
C. integral dose
D. cumulative dose
B. exit dose
Rationale:
The dose at the point where the beam comes out of the patient is the exit dose.
172
An excerpt from an equivalent square table shows: Using the table, the equivalent square for a field size 9.5 x 13 would be:
A. 10.6
B. 10.9
C. 11.3
D. 11.45
B. 10.9
Rationale:
Using interpolation between the values 10.6 and 11.3. Take the average to get 10.95.
173
If the pituitary gland is treated using a three-field technique, including laterals and vertex fields, wedges will be used in:
A. the lateral fields
B. all three fields
C. the vertex field
D. none of the fields
A. the lateral fields
Rationale:
Due to the contour of the skull in the coronal plane, wedges would be used in the lateral fields only for a midline tumor such as one located in the pituitary gland.
174
Assuming ideal patient contour, the optimal hinge angle for a 45 degree wedged pair is:
A. 30 degrees
B. 45 degrees
C. 60 degrees
D. 90 degrees
D. 90 degrees
Rationale:
Use the formula: hinge = 180 - 2(wedge angle).
175
A tumor lethal dose is 5000 cGy. The spinal cord is adjacent to the tumor. The approximate therapeutic ratio is:
A. 0.9
B. 1
C. 1.11
D. 2.1
A. 0.9
Rationale:
Therapeutic ratio is normal tissue tolerance/tumor lethal dose. Without considering the volume of cord irradiated, the accepted tolerance is 45 Gy. 45/50 = 0.9.
176
The most likely photon beam energy used to treat areas in the head and neck would be:
A. 6 MV
B. 10 MV
C. 18 MV
D. 25 MV
A. 6 MV
Rationale:
The anatomy in the head and neck area is thin so the photon energy most likely used would be 6 MV.
177
A 6 MV photon beam on the linear accelerator has an output at isocenter of 1.2 cGy/MU. What would be the inverse square factor used in the monitor unit calculation for an extended distance treatment at 120 cm SSD?
A. 0.677
B. 0.823
C. 1.21
D. 1.48
A. 0.677
Rationale:
The inverse square factor is (SAD/SSD+Dmax)2. Using this formula, the inverse square factor would be 0.677.
178
A dose of 3000 cGy is to be delivered at a depth of 5 cm with a %DD of 85%. What is the applied dose?
A. 3529 cGy
B. 2550 cGy
C. 5550 cGy
D. 6000 cGy
A. 3529 cGy
Rationale:
Use the applied dose formula. Applied dose = TD/%DD. 3000/85% = 3529.
179
An excerpt from an 18 MV TAR chart shows:
The TAR for a field size 11 x 11 at a depth of 4.5 is:
A. 1.009
B. 1.011
C. 2.02
D. 1.006
D. 1.006
Rationale:
Interpolate-take the average-between 10 cm square at 4 cm depth and 12 cm square at 5 cm depth. 1.009 + 1.002 = 2.011/2 = 1.055.
180
A dose of 55 Gy will be given through anterior and lateral ports to the maxillary sinus. The lens is included in the treatment fields. The therapeutic ratio is approximately:
A. 0.9
B. 0.18
C. 5.5
D. 11
B. 0.18
Rationale:
The tolerance dose of the lens ranges from 5 Gy to 10 Gy depending on the source. Use the upper limit of the range and the therapeutic ratio formula: 1000/5500 = 0.18.
181
When planning portal arrangements, it is important to keep in mind that the treatment couch can be rotated:
A. 360 degrees and moved right to left
B. to any position and moved up and down
C. up to 90 degrees and moved up and down and right to left
D. about 180 degrees, moved up and down and right to left
D. about 180 degrees, moved up and down and right to left
Rationale:
Due to the immobile gantry, the treatment couch can be rotated approximately 90 degrees to the right and left of neutral/0 degrees, up and down and right to left, according to safe limits set by the manufacturer.
182
The physical size of the treatment field is defined at the interception of the central axis at the specific isocentric distance and which isodose line?
A. 10%
B. 20%
C. 50%
D. 80%
C. 50%
Rationale:
The geometric field size is defined at isocenter at the interception of the 50% isodose line.
183
A magnification ring measures 5.0 cm on a simulation film. The actual size of the ring is 3.0 cm. The ring was located 85 cm from the target. What is the magnification factor?
A. 0.6
B. 0.85
C. 1.17
D. 1.67
D. 1.67
Rationale:
Using the magnification formula image size/object size = magnification factor. 5/3 = 1.67.
184
Positron Emission Tomography (PET) is based on imaging with photons produced in:
A. pair production
B. annihilation of positrons by electrons
C. fluorescence caused by positrons in certain screens
D. Compton scattering of photons
B. annihilation of positrons by electrons
Rationale:
PET scan images are a result of positron annihilation.
185
When treating opposed oblique fields for a lung tumor:
A. SSDs for each field should be documented and verified.
B. SSDs for each field should be the same and verified.
C. Isocenter should be at the mid point of the tumor.
D. Isocenter should be at midline of the patient.
A. SSDs for each field should be documented and verified
Rationale:
Oblique fields for the treatment of lung tumors will not necessarily be at the midpoint of the tumor or the midline of the patient's measured separation. Oblique fields should be verified against the treatment plan and SSD reading documented
186
What thickness of cerrobend would be equivalent to 8 cm of lead?
A. 6.7
B. 7
C. 9.6
D. 12
C. 9.6
Rationale:
Cerrobend is about 15% less dense than lead. To figure the equivalent attenuation of cerrobend to lead, use the factor 1.2. 1 cm lead = 1.2 cm cerrobend.
187
For a sloping skin surface, even dose distribution and maintenance of skin sparing using a high energy beam can be achieved by using a:
A. wedge
B. bolus
C. laser
D. wider beam
A. wedge
Rationale:
A sloping skin surface will cause inhomogeniety of dose lines. A wedge can be inserted to even dose distribution while, at the same time, maintaining skin sparing.
188
If the exposure rate at 1 meter is 53.7 R/minute, at what distance is the exposure rate 35 R/minute?
A. 0.5 meters
B. 0.75 meters
C. 1.53 meters
D. 1.24 meters
D. 1.24 meters
Rationale:
Using the inverse square formula. 53.7/35 = 12 /x2, 1.53 = x2; x = 1.24.
189
The backscatter factor depends on (select two):
1. field size
2. distance
3. energy
4. time
1. field size
3. energy
Rationale:
The backscatter or peak scatter factor is dependent on the field area and energy of the beam.
190
Total dose to the lumpectomy site following accelerated partial breast irradiation utilizing high dose rate brachytherapy will be approximately:
A. 20 Gy
B. 35 Gy
C. 45 Gy
D. 60 Gy
C. 45 Gy
Rationale:
Using APBI techniques, dose to the lumpectomy site typically ranges from 40-50 Gy.
191
The dDmax dose for a 250 cGy tumor dose if the depth dose percentage is 96% would be:
A. 240
B. 260
C. 300
D. 350
B. 260
Rationale:
Using the applied dose formula. Applied dose = TD/%DD. 250/96% = 260.
192
An 8 MeV electron beam will be used to deliver 300 cGy to Dmax. The SSD is 100 cm, dose rate for 10 x 10 is 1.0 cGy/MU, an 8 x 8 cm cone will be used and the cone factor is 0.872. What MU setting should be used?
A. 344 MU
B. 430 MU
C. 172 MU
D. 3.44 MU
A. 344 MU
Rationale:
Using the monitor unit formula: 300/1 x .872 x 1.00 = 344 MU.
193
For a field treated with the isocenter at a depth of 12.5 cm on a 100 cm SAD linear accelerator, the collimator setting is 20 x 25. The field would measure ______ on the patient's skin surface.
A. 20 x 25
B. 7.5 x 12.5
C. 17.5 x 21.9
D. 22.9 x 28.6
C. 17.5 x 21.9
Rationale:
Use direct proportion. Figure the SSD: 100-12.5 = 87.5 cm. The collimator setting is the measured field size at isocenter. 20:100 as x:87.5. Do the same for the length.
194
Clarkson's method is used to determine the scatter produced in:
A. irregular fields
B. rectangular fields
C. square fields
D. extended fields
A. irregular fields
Rationale:
Clarkson's method is for use in irregular fields.
195
The closest blocked equivalent square for a 10 x 20 rectangular field with a 4 x 6 block in the field is:
A. 8.6
B. 11.4
C. 13.3
D. 15.6
C. 13.3
Rationale:
Subtract the area of the block from the area of the open field, and then take the square root. 10 x 20 = 200, 4 x 6 = 24. 200-24 = 176. The square root of 176 = 13.3.
196
The closest blocked equivalent square for a 10 x 20 rectangular field with a 4 x 6 block in the field is:
A. 8.6
B. 11.4
C. 13.3
D. 15.6
C. 13.3
Rationale:
Subtract the area of the block from the area of the open field, and then take the square root. 10 x 20 = 200, 4 x 6 = 24. 200-24 = 176. The square root of 176 = 13.3.
197
What is the CT number of water on a Hounsfield scale?
A. 1000
B. -1000
C. 0
D. -3000
C. 0
Rationale:
The CT number of water is 0.
198
The skin dose, in the case of electron beams, is about:
A. 80% to 90%
B. 30% to 40%
C. 100%
D. 10%
A. 80% to 90%
Rationale:
Electron beams do have some skin sparing. Skin dose is usually 80% to 90% of dose.
199
The treatment plan for an esophagus calls for a total dose of 3000 cGy to the AP field, 1500 cGy to the RPO field, and 1500 cGy to the LPO field. The prescription is for a total of 6000 cGy to be delivered in 40 fractions. What will the daily dose be to each field AP:RPO:LPO?
A. 100:50:50
B. 150:150:150
C. 50:100:100
D. 75:37.5:37.5
D. 75:37.5:37.5
Rationale:
This plan calls for unequal weighting. Each fraction should deliver a total of 150 cGy. The AP field is weighted at 50% of the total. 150 x 50% = 75. The remaining 75 will be equally distributed between the oblique fields. 75/2 = 37.5. Check your work. Dose for each field should total 150 cGy.
200
Shoulder retractors are important for:
A. pushing the shoulder into the treatment field
B. pulling the shoulders out of the treatment field
C. improving dose uniformity
D. patient comfort during long procedures
B. pulling the shoulders out of the treatment field
Rationale:
Shoulder retractors are used to pull shoulders down out of the field.
201
In one month, the output of a cobalt machine would reduce by about:
A. 0.1%
B. 1%
C. 2%
D. 5%
B. 1%
Rationale:
Cobalt output decreases at about 1% a month.
202
The natural slope of the chest may cause high dose regions in the upper mediastinum. This area of increased dose may be managed by the use of a:
A. bolus
B. custom compensator
C. bite block
D. wing board
B. custom compensator
Rationale:
The slope of the chest causes uneven dose distribution leading to higher dose regions in the upper mediastinum, where the anatomy is thinner. Custom compensators, standard wedges, or dynamic wedges may be used to produce more even dose distribution.
203
A representation of the dose in an irradiated volume, as a function of spatial position along a single line is known as a/an:
A. isodose curve
B. percent depth dose line
C. dose profile
D. dose volume histogram
C. dose profile
Rationale:
A dose profile shows the dose in a volume as a function of position along a single line.
204
When it is determined that an immobilization device is needed, the therapist should:
A. make the device, then determine beam orientation
B. determine beam orientation, then make the device
C. determine device, patient position, and then beam orientation
D. make the device, then determine patient position
B. determine beam orientation, then make the device
Rationale:
Before fabricating a device, the therapist should consider the most appropriate patient position, likely beam orientation, and then which device.
205
Which of the following is not a necessary step in tumor volume definition?
A. contour of the tumor highlighted throughout the patient volume
B. measurements of anatomical separation
C. staging of the disease
D. identification of adjacent normal tissue
C. staging of the disease
Rationale:
In defining the tumor volume, patient measurements are taken, visible tumor margins are highlighted, and normal adjacent tissue is identified.
206
The calculated treatment time on a cobalt unit is 4.23 minutes. This treatment time in minutes and seconds is:
A. 4 minutes 23 seconds
B. 4 minutes 30 seconds
C. 4 minutes 14 seconds
D. 4 minutes 19 seconds
C. 4 minutes 14 seconds
Rationale:
Use direct proportion. 60 sec 1 minute as x sec: 0.23 minutes.
207
The depth of inguinal lymph nodes :
A. can range from 5 to 10 cm and is not influenced by patient size
B. is at approximately 4 cm from the surface in all patients
C. can range from 2 to 18 cm depending on patient size
D. is always one-third of the patient's anterior to posterior separation
C. can range from 2 to 18 cm depending on patient size
Rationale:
There are both deep and superficial inguinal lymph nodes located from 2 to 18 cm deep depending on the patient's size.
208
For breast irradiation, internal mammary lymphatics would be best treated using:
A. an anterior 10 MV photon field
B. widened tangential fields
C. an anterior electron field
D. a posterior electron field
C. an anterior electron field
Rationale:
Internal mammary lymphatics may be included in tangential fields; however this would increase lung volume. An anterior field could be matched to tangential fields using low-energy photons or electron beam. The electron beam would be best so that dose to limit dose to the mediastinum. Internal mammary nodes are located approximately 3 cm below the anterior surface in patients of normal body habitus.
209
The range of a 10 MeV electron beam in tissue is approximately:
A. 10 mm
B. 10 cm
C. 5 cm
D. none of the above
C. 5 cm
Rationale:
The range of an electron beam can be found by dividing the energy by 2.
210
During CT simulation, laser alignment marks should be placed:
A. at the level of anticipated treatment isocenter
B. at the level of the central scan
C. at the first image level
D. at the final image level
A. at the level of anticipated treatment isocenter
Rationale:
Markings should be placed at the level of the anticipated treatment isocenter during CT simulation.
211
External beam radiation for cancers of the midesophagus is best delivered using:
A. anterior field only
B. right and left lateral fields
C. posterior and two posterior obliques
D. anterior and two posterior obliques
D. anterior and two posterior obliques
Rationale:
Feedback: The middle section of the esophagus is best treated with an anterior and two posterior obliques to adequately deliver dose to the volume while sparing the dose-limiting spinal cord.
212
A field area measures 14 x 23 at a distance of 80 cm. What is the measured field size at a distance of 60 cm?
A. 10.5 x 17.25
B. 18.6 x 30.6
C. 25 x 41
D. 7.9 x 12.9
A. 10.5 x 17.25
Rationale:
Use direct proportion.
213
A midline brain tumor will be treated to 4500 cGy, through right and left lateral ports. Of concern is the normal brain tissue. The therapeutic ratio is approximately:
A. 0.75
B. 1
C. 1.33
D. 1.5
C. 1.33
Rationale:
Therapeutic ratio is normal tissue tolerance/tumor lethal dose. The tolerance of brain tissue is accepted as 60 Gy. 60/45 = 1.33.
214
The depth of electronic equilibrium for a 10 MV photon beam is:
A. 0.5 cm
B. 1.0 cm
C. 1.5 cm
D. 2.0 cm
D. 2.0 cm
Rationale:
The depth of electronic equilibrium for a 10 MV beam is 2.0 cm.
215
What is the first objective in radiation therapy treatment planning?
A. identify routes of tumor spread and beam energy
B. define critical structures and beam angles
C. determine tumor boundaries and critical structures
D. choose beam energy and angles
C. determine tumor boundaries and critical structures
Rationale:
The first objective of treatment planning is to define the tumor volume and identify critical structures and where they lie in respect to the tumor volume.
216
A method of radiation therapy in which the source is moved around the patient, but only through certain sectors of a circle is called:
A. step and shoot
B. arc therapy
C. adjacent field technique
D. feathering technique
B. arc therapy
Rationale:
Arc therapy is a method of radiation therapy delivery in which the source is moved around the patient through certain sectors of a circle.
217
Standard wedges are designed for use in high voltage beams and vary in angle from_____to____degrees.
A. 15 to 75
B. 30 to 60
C. 45 to 75
D. 15 to 60
D. 15 to 60
Rationale:
Standard wedges vary in size from 15 to 60 degrees.
218
Isodose curves would shift away from the skin surface for underlying:
1. lung
2. air cavities
3. bone
A. 1, 2
B. 2, 3
C. 1, 3
D. 1, 2, 3
A. 1, 2
Rationale:
Isodose lines would shift away from the skin surface for underlying lung tissue or air-filled cavities.
219
Increasing the field size from 5 x 5 to 20 x 20, with all other factors remaining the same, the percent depth dose will:
A. increase
B. decrease
C. remain the same
D. move the Dmax point
A. increase
Rationale:
Increasing the field size will increase the percent depth dose.
220
The volume larger than the treatment volume receiving some significant dose is the:
A. tumor volume
B. target volume
C. irradiated volume
D. clinical volume
C. irradiated volume
Rationale:
The volume receiving some dose that is larger that the treatment volume is the irradiated volume.
221
When using film for portal imaging, the size of the enlarged image or shadow on the film is dependent on:
1. target-to-object distance
2. object-to-table distance
3. target-to-film distance
A. 1, 2
B. 2, 3
C. 1, 3
D. 1, 2, 3
C. 1, 3
Rationale:
Magnification of objects on film depends on target-to-object distance, target-to-film distance, and object-to-film distance.
222
If a patient has a large pelvic tumor involving the bladder and prostate, and there is a presacral mass, the best arrangement would be:
A. opposed anterior and posterior fields
B. opposed lateral fields
C. four-field box technique
D. 90 degree wedged pair
A. opposed anterior and posterior fields
Rationale:
In this instance, the goal would be to treat all areas of tumor at various depths in the patient's pelvis. At least, the initial fields would be opposing anterior and posterior fields to give even dose to all points of interest and spare pelvic bones.
223
In radiation therapy planning, the x, y, z coordinate system is used to:
A. align patients daily for treatment
B. describe a point in space relative to isocenter
C. describe the location of isocenter
D. assure all planes are parallel
B. describe a point in space relative to isocenter
Rationale:
The x, y, z coordinate system is used to describe the location of a point in space relative to isocenter.
224
Partial breast irradiation may involve treatment techniques that employ all of the following except:
A. 5-field breast technique
B. brachytherapy
C. 3-D conformal IMRT
D. intraoperative radiation therapy
A. 5-field breast technique
Rationale:
Partial breast irradiation may be accomplished by using brachytherapy, intra-operative therapy, or 3-D conformal IMRT.
225
Electron beams are useful in radiation therapy primary because they:
A. have a greater biological effect that X-rays
B. provide more skin sparing than gamma rays
C. have a definite range in tissue
D. have maximum LET at electronic equilibrium
C. have a definite range in tissue
Rationale:
Electrons have a definite range in tissue, making them useful in the treatment of superficial lesions with critical tissues beyond.
226
An 8 MeV electron beam is used to deliver 200 cGy to the 80% dose line. The field size is 8 x 8 and the SSD is 100 cm. The dose rate is 1.0 cGy/MU for a 10 x 10 field. The cGy/Mu for this cone size is 0.872. What are the calculated monitor units?
A. 229 MU
B. 287 MU
C. 143 MU
D. 115 MU
B. 287 MU
Rationale:
Using the monitor unit formula: 200/1 x 0.872 x 0.80 = 287 MU.
