MDCB questions and Answers Graded A+
The development of which of the following conditions is an example of a stochastic effect of
radiation? second primary
A dose of 30 Gy in 10 fractions to a depth of 7 cm from a 6 MV single posterior field using an
isocentric technique at 100 cm source-to-axis distance (SAD). The patient was incorrectly treated
five times at 100 cm source-to-surface distance (SSD). The approximate dose at 7 cm after five
fractions is: 3gyx(100/107)^2=2.6x5=13.1gy
A 20 cm diameter patient is treated to midplane by using a 100 cm source-to-axis distance (SAD)
technique. If the same patient is then treated by using a 100 cm source-to-surface distance (SSD)
technique, the monitor units would increase by approximately: (110/100)^2=1.21= 21%
If a field has a jaw setting to produce a 40 cm x 40 cm field at 100 cm from the source, at what
distance from the source will the field size measure 200 cm x 200 cm? 40/100=200/x
(100x200)/40=500
What is the approximate density of healthy tissue? 0.30 g/cc
, The accelerator component that ejects electrons in to the linear accelerator is? Electron
gun
Radiation damage to the fetus resulting in severe birth defects would most often occur when
radiation was delivered at which time post-fertilization? 3-12 Weeks
The decay constant for a radioactive source that has a half-life of 60 days is?
.693/60=0.0155 or 0.012
The function of a maze to a megavoltage treatment room is to: minimize radiation levels
at the door
The anatomic location of the seminal vesicles is: superior to the prostate and angled
posteriorly near the rectum.
Two missed treatment days due to LINAC malfunction: may be compensated by adding
the same or even more fractions to the treatment course with weekend treatment if possible.
The development of which of the following conditions is an example of a stochastic effect of
radiation? second primary
A dose of 30 Gy in 10 fractions to a depth of 7 cm from a 6 MV single posterior field using an
isocentric technique at 100 cm source-to-axis distance (SAD). The patient was incorrectly treated
five times at 100 cm source-to-surface distance (SSD). The approximate dose at 7 cm after five
fractions is: 3gyx(100/107)^2=2.6x5=13.1gy
A 20 cm diameter patient is treated to midplane by using a 100 cm source-to-axis distance (SAD)
technique. If the same patient is then treated by using a 100 cm source-to-surface distance (SSD)
technique, the monitor units would increase by approximately: (110/100)^2=1.21= 21%
If a field has a jaw setting to produce a 40 cm x 40 cm field at 100 cm from the source, at what
distance from the source will the field size measure 200 cm x 200 cm? 40/100=200/x
(100x200)/40=500
What is the approximate density of healthy tissue? 0.30 g/cc
, The accelerator component that ejects electrons in to the linear accelerator is? Electron
gun
Radiation damage to the fetus resulting in severe birth defects would most often occur when
radiation was delivered at which time post-fertilization? 3-12 Weeks
The decay constant for a radioactive source that has a half-life of 60 days is?
.693/60=0.0155 or 0.012
The function of a maze to a megavoltage treatment room is to: minimize radiation levels
at the door
The anatomic location of the seminal vesicles is: superior to the prostate and angled
posteriorly near the rectum.
Two missed treatment days due to LINAC malfunction: may be compensated by adding
the same or even more fractions to the treatment course with weekend treatment if possible.
