DOS UNIT 3 EXAM QUESTIONS & ANSWERS
Which of the following remains constant for isocentric treatments?
a. SSD
b. energy
c. SAD
d. field size - Answer -SAD
Percent depth dose decreases with - Answer -increasing depth
Field matching techniques used in the treatment of the craniospinal axis include all of
the following exept:
a. turning the collimator for the lateral brain fields
b. kick the couch for lateral brain fields
c. turn the collimator for the PA spine field
d. shifting junctions 22-3 times during the course of treatment
e. all of the above are field matching techniques used in craniospinal irradiation -
Answer -c. turn the collimator for the PA spine field
The size at which a hot spot starts to be considered clinically significant is - Answer -
2cm^2
Mayneord's F factor is used to correct PDD for changes in - Answer -distance
A craniospinal case as planned for a tall, 12 year old child. His spone field required a
treatment field of 8x48cm at the skin surface. The limit of the collimator on a 100cm
isocentric linac is 40x40cm. What is the required extended distance for this case? -
Answer -120 cm (40/100= 48/x)
What are the two classes of wedge filters? - Answer -physical and nonphysical
The dose distribution below is a result of breast tangents planned with a 15-degree
wedge. Which of the following statements is true? (theres a picture but the free version
doesn't allow me to upload it :/ #12 on exam 3)
a. the isodose distribution could be improved if mixed with an open field
b. the plan is underwedged and the isodose distribution could be improved if a larger
wedge angle were used
c. the plan is overweighted and the isodose distribution could be improved if a smaller
wedge angle were used
d. the isodose distribution could be improved if the wedges were flipped
, e. the isodose distribution cannot be improved - Answer -b. the plan is underwedged
and the isodose distribution could be improved if a larger wedge angle were used
A palliative lung pt is being treated with AP/PA fields using isocentric technique. If the
posterior SSD is 87.3 cm, what is the anterior SSD if the pt is 29.5 cm thick. - Answer -
83.2 cm
The presence of a wedge filter _________________ the output of the machine -
Answer -decreases
The optimal wedge angle for 2 fields is determined to be 15 degrees. What is the hinge?
- Answer -150 degrees
When treating with photons, treatment accessories should always remain ______ from
the surface of the patient. - Answer -15-20 cm
Which of the following could be used as a strategy to achieve the goals of treatment
planning? Select all that apply:
a. beam weighting factor
b. increasing number of fields
c. beam modifiers
d. Adjusting field size - Answer -all of them
Where is a universal wedge placed? - Answer -above secondary collimator
If a patient is treated with an energy of 6 MV and a 1cm bolus is placed on the pt's skin,
where is the Dmax located, relative to the skin surface? - Answer -0.5 cm deep to the
skin
Divergence causes an __________ in field size as the distance from the source
increases. - Answer -an increase
Nonphysical wedge systems create a wedge effect by the use of - Answer -
independent/ asymmetric jaws
MLCs (I marked this and she put that is was "ok")
Which of the following factors is not used when calculating the monitor units for an
isocentric (SAD) treatment?
a. TMR
b. Collimator scatter factor
c. BSF
d. PDD
e. Phantom scatter factor
f. output factor (reference dose rate) - Answer -c. BSF
d. PDD
Which of the following remains constant for isocentric treatments?
a. SSD
b. energy
c. SAD
d. field size - Answer -SAD
Percent depth dose decreases with - Answer -increasing depth
Field matching techniques used in the treatment of the craniospinal axis include all of
the following exept:
a. turning the collimator for the lateral brain fields
b. kick the couch for lateral brain fields
c. turn the collimator for the PA spine field
d. shifting junctions 22-3 times during the course of treatment
e. all of the above are field matching techniques used in craniospinal irradiation -
Answer -c. turn the collimator for the PA spine field
The size at which a hot spot starts to be considered clinically significant is - Answer -
2cm^2
Mayneord's F factor is used to correct PDD for changes in - Answer -distance
A craniospinal case as planned for a tall, 12 year old child. His spone field required a
treatment field of 8x48cm at the skin surface. The limit of the collimator on a 100cm
isocentric linac is 40x40cm. What is the required extended distance for this case? -
Answer -120 cm (40/100= 48/x)
What are the two classes of wedge filters? - Answer -physical and nonphysical
The dose distribution below is a result of breast tangents planned with a 15-degree
wedge. Which of the following statements is true? (theres a picture but the free version
doesn't allow me to upload it :/ #12 on exam 3)
a. the isodose distribution could be improved if mixed with an open field
b. the plan is underwedged and the isodose distribution could be improved if a larger
wedge angle were used
c. the plan is overweighted and the isodose distribution could be improved if a smaller
wedge angle were used
d. the isodose distribution could be improved if the wedges were flipped
, e. the isodose distribution cannot be improved - Answer -b. the plan is underwedged
and the isodose distribution could be improved if a larger wedge angle were used
A palliative lung pt is being treated with AP/PA fields using isocentric technique. If the
posterior SSD is 87.3 cm, what is the anterior SSD if the pt is 29.5 cm thick. - Answer -
83.2 cm
The presence of a wedge filter _________________ the output of the machine -
Answer -decreases
The optimal wedge angle for 2 fields is determined to be 15 degrees. What is the hinge?
- Answer -150 degrees
When treating with photons, treatment accessories should always remain ______ from
the surface of the patient. - Answer -15-20 cm
Which of the following could be used as a strategy to achieve the goals of treatment
planning? Select all that apply:
a. beam weighting factor
b. increasing number of fields
c. beam modifiers
d. Adjusting field size - Answer -all of them
Where is a universal wedge placed? - Answer -above secondary collimator
If a patient is treated with an energy of 6 MV and a 1cm bolus is placed on the pt's skin,
where is the Dmax located, relative to the skin surface? - Answer -0.5 cm deep to the
skin
Divergence causes an __________ in field size as the distance from the source
increases. - Answer -an increase
Nonphysical wedge systems create a wedge effect by the use of - Answer -
independent/ asymmetric jaws
MLCs (I marked this and she put that is was "ok")
Which of the following factors is not used when calculating the monitor units for an
isocentric (SAD) treatment?
a. TMR
b. Collimator scatter factor
c. BSF
d. PDD
e. Phantom scatter factor
f. output factor (reference dose rate) - Answer -c. BSF
d. PDD
