Which of the following areas should be included when irradiating a tumor of the nasopharynx?
I. nasopharynx proper
II. retropharyngeal nodes
III. base of the skull
All of the above
During a treatment calling for a tangential beam with a steep grazing incidence, the surface dose build-up is _________ (equal/not equal) to the entrance dose.
Equal
All of the following areas require the treatment of the surrounding lymphatics, EXCEPT for the T1 - T2 tumors involving the:
B. Larynx
The amount of geometric penumbra is NOT effected by the:
C. Field size
The rational behind using lower than 100% isodose curve for irradiation of the chest wall using an electron beam is:
1. increased skin sparing
2. lower lung exposure
3. reduced bolus use
2. Lower lung exposure
Ultrasound provides useful information for patient contours of the following structures, EXCEPT:
A. Lung tissue
A wedge pair technique may effectively treat to a tumor depth of:
0-7 cm
When a wedge pair technique is used, an acceptable value for a high dose region (hot spot) would be _____%.
10%
"Negative" shield blocks are more commonly used for treating tumors of the:
C. head & neck
During a 4 mV treatment, a sloping skin surface is corrected by a ________ shift toward the skin surface of the isodose curve.
2/3
The ICRU considers the minimum accuracy of the delivered dose to be ____% of the prescribed dose.
5%
The caudal margin of the target volume in patients with endometrial cancer is:
B. mid-obturator foramen
During rotation therapies with an arc angle of 100°, the point of maximum dose is normally located displaced ________ (toward/away from) the irradiated sector.
Toward
Tumors that are limited to the upper cervical esophagus are best treated with:
B. Three field technique with posterior obliques
A half value layer thickness for a 10 MeV photon energy is about ______ mm Pb.
13 mm Pb
What is the formula used to find Dmax from percentage depth dose?
The 6 field Stanford technique is most often applied to:
B. cutaneous lymphoma
During XRT of a pituitary tumor with the patient supine, the anterior field should enter:
A. above & behind the eyes
The target volume for carcinoma of the prostate may include the following regional lymph nodes:
I. Obturator
II. External iliac
III. Internal iliac
All of the above
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. 44% overdose
In treatment of the mediastinum, following a right lung pneumonectomy, the oblique field should enter on the _________ (right/left) side.
Right side
The principle concern in localizations of breast lesions is the:
D. position of underlying lung
Radiotherapy is most often indicated for carcinoma of the __________ portion of the esophagus.
B. upper
During a radiotherapy of the uterus using a 4 field box technique, which field includes the entire urinary bladder?
1. anterior 2. posterior 3. lateral
B. 2 & 3
Posterior & lateral
During XRT of the esophagus, rotational and arc therapy is usually NOT possible because of the:
1. heart movement 2. spinal curvature 3. position of the esophagus
A. 2 & 3
curvature of the spine and position of the esophagus
The AP/PA "stop sign" field is most often used in the treatment of:
Prostate ca
In order to include the hypogastric nodes in a lateral field of the pelvis, the posterior margin should transect the:
C. rectum
The TAR at Dmax is:
1. always less than or equal to 0
2. the backscatter factor
3. dependent on field size
C. all of the above
An increase in field size will increase dose in the ______ region.
Build-up
The Maynoerd F factor for a given energy is dependent upon material's:
A. atomic number
The energy range for photon beams above 2 MeV should be measured by:
B. isodose data
The amount of backscattering that occurs in a given treatment volume will increase as the:
1. field size increases 2. beam quality increases 3. Dmax increases
C. field size increases
The amount of backscatter at the depth of the depth maximum becomes negligibly small at beam energies above:
D. 8 mV
The scatter-air ratio (SAR) may be used in the determination of the scattered dose produced in:
1. square fields 2. irregular fields 3. circular fields
B. all of the above
An isodose curve can be employed to obtain measurements of the depth dose percentage as a function of the transverse distance from the:
C. central axis
When verifying an isodose chart using a water phantom, the acceptable amount of deviation is considered to be ______ or less in depth up to 20 cm.
B. 2%
Calculate the Dmax dose for a patient receiving 300 cGy/day for a single AP port to a depth of 8 cm. The PDD is 69.3%
432 cGy
The backscatter factor (BSF) depends on:
1. SSD 2. Beam quality 3. Field size
C. Beam quality and Field size
The Clarkson method is useful in the determination of the scatter produced in __________ fields.
Irregular fields
The ratio of dose at a given point in a medium to the dose at the same point in free space is called the:
C. tissue-air ratio (TAR)
Central axis depth dose distribution depends on beam energy, so the depth of a given isodose curve ________ (increases/decreases) with beam energy.
Increases
A bulge on the lateral region of the isodose curve at depth is most often associated with:
A. low energy beams
The sharpness of a shielding block gradient is dependent upon:
1. beam energy 2. block material 3. block divergence
A. Beam energy & Block divergence
The reduction of block transmission penumbra can be accomplished by:
D. employing divergent blocks
In general, when shielding blocks are employed, the acceptable amount of primary beam transmission is approximately:
D. 5%
During a wedge pair technique, hot spots are most commonly located near the:
C. thin edge of the wedge
Which of the following devices is employed to help obtain proper alignment of a treatment beam?
C. front/back pointer
The material most suitable for the reduction of electron contamination in megavoltage units is:
D. tin
The minimum thickness for blocks for a Cobalt 60 machine is:
C. 5 cm lead
Which of the following block designs permits the longest SSD?
A. divergent blocks
In order to produce the least amount of electron contamination from a shadow tray, the material should have a atomic number of about:
B. 50
In order to achieve a 5% or smaller block transmission, it must have a thickness of about:
D. 5.0 HVL
The required thickness for a cerrobend block for a narrow photon beam in the 2-22 mV range is about:
A. 7.5 cm
The main advantage of using Lipowitz metal over lead for blocks is that it:
D. Has a lower melting point
The tissue most likely to receive the highest dose at a bone tissue interface is bone mineral surrounded by __________.
