Dosimetry Board Review questions with verified
answers
A cerrobend block, 5.5 cm thick, 10.0 cm wide, and 10.0 cm long, was
used to shield a field on a patient who was treated on an 18 MV linear
accelerator. If 4000 cGy in 20 fractions would be delivered to dmax in
the open field, what is the approximate dmax dose to the center of the
shielded area under the block? Ans✓✓✓ 360 cGy
A patient is receiving radiation to the chest. The calculated dose to the
tumor while "on cord" is 35 Gy at 2.5 Gy per fraction. The cord is
receiving 3 Gy per fraction. Assuming alpha/beta of 3 for late effects,
what is the cord equivalent dose at 2 Gy per fraction? Ans✓✓✓ 50 Gy
A photon field abutting an electron field at the skin surface will result in
a: Ans✓✓✓ photon side hot spot and electron side cold spot
According to the AAPM TG-40, what is the minimum recommended
frequency and percentage tolerance for checking x-ray beam symmetry
on the linear accelerator? Ans✓✓✓ Monthly, +/- 3%
According to The Quantitative Analysis of Normal Tissue Effects in the
Clinic (QUANTEC) review, what is the percentage rate of optic
neuropathy when treating the optic nerve to a dose greater than 60 Gy
with conventional fractionation? Ans✓✓✓ >7 and < 20
, Based on the ratio of linear quadratic terms (alpha/beta model) in
multifraction experiments, which of the following tissues would be
classified as an early responding tissue? Ans✓✓✓ skin
Craniospinal irradiation is to be performed using a PA spine port (100
cm SSD, 38.0 cm long) and right/left lateral brain ports (100 cm SAD,
18.0 cm long). How many degrees must the collimator and the table be
rotated to make sure all beam edges match? Ans✓✓✓ <coll = tan(-1)
(.5L1 x 1/SSD)
<couch = tan(-1) (.5L2 x 1/SAD)
Collimator 10.8 degrees, Couch 5.1 degrees
Examples of radiation-induced, chronic skin changes do NOT include:
Ans✓✓✓ moist desquamation.
For which of the following malignancies has hyperfractionated radiation
therapy been shown to significantly improve local control compared
with standard fractionation? Ans✓✓✓ head and neck cancer
ICRU -62 is a method of delineation of an Internal Target Volume (ITV)
to provide extra margin for: Ans✓✓✓ anatomy that may move with
respiration and breathing
answers
A cerrobend block, 5.5 cm thick, 10.0 cm wide, and 10.0 cm long, was
used to shield a field on a patient who was treated on an 18 MV linear
accelerator. If 4000 cGy in 20 fractions would be delivered to dmax in
the open field, what is the approximate dmax dose to the center of the
shielded area under the block? Ans✓✓✓ 360 cGy
A patient is receiving radiation to the chest. The calculated dose to the
tumor while "on cord" is 35 Gy at 2.5 Gy per fraction. The cord is
receiving 3 Gy per fraction. Assuming alpha/beta of 3 for late effects,
what is the cord equivalent dose at 2 Gy per fraction? Ans✓✓✓ 50 Gy
A photon field abutting an electron field at the skin surface will result in
a: Ans✓✓✓ photon side hot spot and electron side cold spot
According to the AAPM TG-40, what is the minimum recommended
frequency and percentage tolerance for checking x-ray beam symmetry
on the linear accelerator? Ans✓✓✓ Monthly, +/- 3%
According to The Quantitative Analysis of Normal Tissue Effects in the
Clinic (QUANTEC) review, what is the percentage rate of optic
neuropathy when treating the optic nerve to a dose greater than 60 Gy
with conventional fractionation? Ans✓✓✓ >7 and < 20
, Based on the ratio of linear quadratic terms (alpha/beta model) in
multifraction experiments, which of the following tissues would be
classified as an early responding tissue? Ans✓✓✓ skin
Craniospinal irradiation is to be performed using a PA spine port (100
cm SSD, 38.0 cm long) and right/left lateral brain ports (100 cm SAD,
18.0 cm long). How many degrees must the collimator and the table be
rotated to make sure all beam edges match? Ans✓✓✓ <coll = tan(-1)
(.5L1 x 1/SSD)
<couch = tan(-1) (.5L2 x 1/SAD)
Collimator 10.8 degrees, Couch 5.1 degrees
Examples of radiation-induced, chronic skin changes do NOT include:
Ans✓✓✓ moist desquamation.
For which of the following malignancies has hyperfractionated radiation
therapy been shown to significantly improve local control compared
with standard fractionation? Ans✓✓✓ head and neck cancer
ICRU -62 is a method of delineation of an Internal Target Volume (ITV)
to provide extra margin for: Ans✓✓✓ anatomy that may move with
respiration and breathing
