Dosimetry Final Exam Actual Questions
and Answers 2026
What are the three components of the penumbra? -
correct answer ✅geometry, transmission, and lateral scattering
Geometric Penumbra -
correct answer ✅is due to the finite source size. It is more of a
concern in Co-60 machines where the source is between 1 and 2
cm in size.
Transmission Penumbra -
correct answer ✅is due to the transmission of photons through
the primary, secondary, or tertiary collimators
Lateral Scattering -
correct answer ✅is the scatters from the irradiated volume at the
field edges
Physical Penumbra -
correct answer ✅is a combination of the geometric penumbra,
transmission penumbra, and the scattering at the beam edges
What is the dose at 10 cm/30 cm off-field-edge distance, relative to
the central axis dose, respectively? -
,Dosimetry Final Exam Actual Questions
and Answers 2026
correct answer ✅Dose at 10 cm away from the field edge is 1% of
the dose at the central axis. Dose at 30 cm away from the field edge
is 0.1% of the dose at the central axis.
What is an isodose chart? -
correct answer ✅a two dimensional representation of dose
distribution. It combines the depth dose and the beam profiles at
various depths. They are formed by lines drawn along equal
increments of percent dose, relative to a particular point, for
example, to dmax along the central axis.
In which radiotherapy treatments is the single field technique
used? -
correct answer ✅It could be used for the treatment of
Supraclavicular, internal mammary nodes, and spinal cord.
What is the tissue lateral effect? -
correct answer ✅Along the central axis, the maximum dose is near
the surface (both surface), rather than on the mid- plane. The ratio
of the peripheral max. dose (or the central axis maximum dose) to
the mid-plane dose (or the midpoint dose) is greater than 1.
,Dosimetry Final Exam Actual Questions
and Answers 2026
How does the ratio of the central axis maximum dose to the
midpoint dose vary with beam energy? -
correct answer ✅the ratio decreases with increasing beam energy
How dose the ratio of central axis maximum dose vary with patient
thickness? -
correct answer ✅the ratio increases with increasing patient
thickness
What is the name of the ultrasound system used in the treatment
rooms of our clinic? For what kinds of radiotherapy treatments is
the ultrasound system used? -
correct answer ✅The ultrasound system is called Clarity. It is a
Elekta product. In our department, Clarity is used for target volume
localization in radiotherapy treatments of prostate and breast
electron boost. It is also used for real time tracking of prostates
(auto scan of trans-perineal ultrasound).
What is the name of the optical localization/tracking system used in
the treatment rooms of our clinic? For what kinds of radiotherapy
treatment is the system used? -
correct answer ✅The optical localization/tracking system is called
AlignRT. Vision RT is the name of the company. AlignRT is one of
their products. AlignRT is used for Deep Inspiration Breath Hold
, Dosimetry Final Exam Actual Questions
and Answers 2026
(DIBH) treatment, lung Stereotactic Ablative Body Radiotherapy
(SABR) treatment, and other treatments where the patient's
breathing need to be monitored.
The total dose delivered at depth dmax from a pair of parallel
opposed fields, expressed as a % of the total dose at mid-plane:
(select all that apply)
A. Decreases as photon energy increases
B. Decreases as field size increases
C. Increases as patient thickness increases
D. Is slightly less for an SSD set up than for an SAD set up -
correct answer ✅A. Decreases as photon energy increases
B. Decreases as field size increases
C. Increases as patient thickness increases
D. Is slightly less for an SSD set up than for an SAD set up
A possible disadvantage of treating a 4-field pelvic brick
isocentrically instead of at SSD is: (select all that apply)
A. Increased set-up time.
B. Field heights are different for AP and laterals.
C. Increased treatment times.
and Answers 2026
What are the three components of the penumbra? -
correct answer ✅geometry, transmission, and lateral scattering
Geometric Penumbra -
correct answer ✅is due to the finite source size. It is more of a
concern in Co-60 machines where the source is between 1 and 2
cm in size.
Transmission Penumbra -
correct answer ✅is due to the transmission of photons through
the primary, secondary, or tertiary collimators
Lateral Scattering -
correct answer ✅is the scatters from the irradiated volume at the
field edges
Physical Penumbra -
correct answer ✅is a combination of the geometric penumbra,
transmission penumbra, and the scattering at the beam edges
What is the dose at 10 cm/30 cm off-field-edge distance, relative to
the central axis dose, respectively? -
,Dosimetry Final Exam Actual Questions
and Answers 2026
correct answer ✅Dose at 10 cm away from the field edge is 1% of
the dose at the central axis. Dose at 30 cm away from the field edge
is 0.1% of the dose at the central axis.
What is an isodose chart? -
correct answer ✅a two dimensional representation of dose
distribution. It combines the depth dose and the beam profiles at
various depths. They are formed by lines drawn along equal
increments of percent dose, relative to a particular point, for
example, to dmax along the central axis.
In which radiotherapy treatments is the single field technique
used? -
correct answer ✅It could be used for the treatment of
Supraclavicular, internal mammary nodes, and spinal cord.
What is the tissue lateral effect? -
correct answer ✅Along the central axis, the maximum dose is near
the surface (both surface), rather than on the mid- plane. The ratio
of the peripheral max. dose (or the central axis maximum dose) to
the mid-plane dose (or the midpoint dose) is greater than 1.
,Dosimetry Final Exam Actual Questions
and Answers 2026
How does the ratio of the central axis maximum dose to the
midpoint dose vary with beam energy? -
correct answer ✅the ratio decreases with increasing beam energy
How dose the ratio of central axis maximum dose vary with patient
thickness? -
correct answer ✅the ratio increases with increasing patient
thickness
What is the name of the ultrasound system used in the treatment
rooms of our clinic? For what kinds of radiotherapy treatments is
the ultrasound system used? -
correct answer ✅The ultrasound system is called Clarity. It is a
Elekta product. In our department, Clarity is used for target volume
localization in radiotherapy treatments of prostate and breast
electron boost. It is also used for real time tracking of prostates
(auto scan of trans-perineal ultrasound).
What is the name of the optical localization/tracking system used in
the treatment rooms of our clinic? For what kinds of radiotherapy
treatment is the system used? -
correct answer ✅The optical localization/tracking system is called
AlignRT. Vision RT is the name of the company. AlignRT is one of
their products. AlignRT is used for Deep Inspiration Breath Hold
, Dosimetry Final Exam Actual Questions
and Answers 2026
(DIBH) treatment, lung Stereotactic Ablative Body Radiotherapy
(SABR) treatment, and other treatments where the patient's
breathing need to be monitored.
The total dose delivered at depth dmax from a pair of parallel
opposed fields, expressed as a % of the total dose at mid-plane:
(select all that apply)
A. Decreases as photon energy increases
B. Decreases as field size increases
C. Increases as patient thickness increases
D. Is slightly less for an SSD set up than for an SAD set up -
correct answer ✅A. Decreases as photon energy increases
B. Decreases as field size increases
C. Increases as patient thickness increases
D. Is slightly less for an SSD set up than for an SAD set up
A possible disadvantage of treating a 4-field pelvic brick
isocentrically instead of at SSD is: (select all that apply)
A. Increased set-up time.
B. Field heights are different for AP and laterals.
C. Increased treatment times.
