CTP1 Exam 2 QUESTIONS AND CORRECT ANSWERS

CTP1 Exam 2 QUESTIONS AND CORRECT
ANSWERS
Percent Depth Dose (PDD) is defined as the dose at depth ddivided by the dose at dmax times
100. PDD=(D_depth/D_max)*100



T/F? - CORRECT ANSWER TRUE



On a dose profile, the field width is defined by the: - CORRECT ANSWER 50%
isodose line



A dose of 180 cGy prescribed to the 92% isodose line is giving what total dose to the
isocenter: - CORRECT ANSWER 196cGy



The wedge angle will:

a. Increase with depth
b. Decrease with depth

c. Does not change with depth

d. Increase and then decrease with depth after dmax - CORRECT ANSWER Decrease
with depth



Wedges can be defined as:

a. Depth at 10cm

b. Depth at dmax

c. Depth of the 50% line
d. Both A and C

e. All of the above - CORRECT ANSWER Both A and C



Factors that affect compensator isodose distributions are - CORRECT ANSWER Depth

Field Size

, Energy

Shape of Compensator



For an average AP/PA patient with a 20cm separation and treated with a 6x beam will have an
approximate hot spot of: - CORRECT ANSWER 15%



Intregal dose should be kept as low as possible in order to minimize toxicities and can be
calculated as the ID=mass*dose:



T/F? - CORRECT ANSWER True



When discussion AP/PA isodose distributions, the hot spot will increase as:

a. Field size increases

b. Separation decreases
c. Energy increases

d. Energy decreases - CORRECT ANSWER Energy decreases



Inhomogeneities in air for an 18MV beam will have a correction factor (%) per cm of lung in
the range of: - CORRECT ANSWER 1-2%



The formula for electron MU calculation is MU=Rx Dose/CF*ROF*ISL*Norm:



T/F? - CORRECT ANSWER True



ROF (Relative Output Factor) are dependent on: - CORRECT ANSWER Energy

Cone size

Cut out size

Shape