MDCB 2025 FINAL EXAM QUESTIONS AND
CORRECT ANSWERS
(T/F) In SAD techniques, the beams are weighted at dmax point. - CORRECT
ANSWERS False
(T/F) In SAD techniques, the beams are weighted at target center. - CORRECT
ANSWERS False
(T/F) Isodose or PDD data can be used directly for a patient, without any modification. -
CORRECT ANSWERS False
(T/F) TAR concept is usually not used with accelerator photon beams because the dose in free
air is not well defined due to conceptual difficulties - CORRECT ANSWERS True
(T/F) TAR can be measured directly or derived from the PDD data. - CORRECT
ANSWERS True
(T/F) In general TAR increases with increase in depth. - CORRECT ANSWERS False
(T/F) At orthovoltage beam quality's (>about 0.5 mm Cu HVL) BSF increases with an increase in
energy. - CORRECT ANSWERS False
(T/F) TAR decreases with increase in field size. - CORRECT ANSWERS False
(T/F) Exit dose calculated using the standard PDD tables would give the correct exit dose. -
CORRECT ANSWERS False
,(T/F) The off axis ratio is the dose at any point in a plane perpendicular to the central axis to that
of the dose on the central axis in that plane. - CORRECT ANSWERS True
(T/F) At a phantom depth of 10 cm, on the central axis, scatter contribution to the dose is more
for an accelerator photon beam compared to a Co-60 beam. - CORRECT ANSWERS False
(T/F) At any depth, the scatter contribution to total dose decreases with increase in incident
photon energy - CORRECT ANSWERS True
(T/F) Cross-beam profile can give information regarding field size, physical penumbra, beam
flatness, and symmetry. - CORRECT ANSWERS True
(T/F) A wedge in motion is known as a dynamic wedge. - CORRECT ANSWERS False
(T/F) The energy fluence of the photons falls according to the inverse square law of distance
with the source position as the origin. - CORRECT ANSWERS True
(T/F) Photon beams have a finite range in a patient. - CORRECT ANSWERS False
(T/F) In the AAPM TG-51 protocol, the electron beam quality is specified by E0 , the mean
energy of the electrons incident on the patient. - CORRECT ANSWERS False
(T/F) The field size dependence of the PDD of an accelerator photon beam is very much
influenced by the electron contamination of the beam - CORRECT ANSWERS True
(T/F) Scatter generally decreases PDD. - CORRECT ANSWERS False
,(T/F) Half blocked tangential breast treatments can be easily accomplished with independent
jaw movements. - CORRECT ANSWERS True
(T/F) One of the advantages of a dynamic wedge over a physical wedge for treatment is that
there is no change in beam quality across the field size. - CORRECT ANSWERS True
(T/F) The tail of the electron beam depth dose distribution is due to some long-range electrons
in the beam. - CORRECT ANSWERS False
(T/F) Electron beams have a finite range in medium. - CORRECT ANSWERS True
(T/F) Low-energy electrons are more easily scattered compared to high-energy electrons. -
CORRECT ANSWERS True
The beam output (cGy/min) measured in air for a Co-60 unit increases with field size mainly due
to:
collimator scatter
room scatter
couch backscatter
chamber wall scatter - CORRECT ANSWERS collimator scatter
Disadvantages of using a physical wedge include:
hardening of the beam, which also depends on wedge thickness
difficulty in positioning the wedge reproducibly in the beam path
, attenuation of the beam and an increase in treatment time
inconvenience in handling heavy wedges - CORRECT ANSWERS hardening of the beam,
which also depends on wedge thickness
attenuation of the beam and an increase in treatment time
inconvenience in handling heavy wedges
In case of isocentric treatment, compared to constant SSD method:
set-up time decreases
set-up error decreases
treatment accuracy increases
overall time to treat a patient increases - CORRECT ANSWERS set-up time decreases
set-up error decreases
treatment accuracy increases
The TAR:
concept is usually not preferred with accelerator photon beams because the dose in free air is
not well defined for these beams
can be derived from PDD data
CORRECT ANSWERS
(T/F) In SAD techniques, the beams are weighted at dmax point. - CORRECT
ANSWERS False
(T/F) In SAD techniques, the beams are weighted at target center. - CORRECT
ANSWERS False
(T/F) Isodose or PDD data can be used directly for a patient, without any modification. -
CORRECT ANSWERS False
(T/F) TAR concept is usually not used with accelerator photon beams because the dose in free
air is not well defined due to conceptual difficulties - CORRECT ANSWERS True
(T/F) TAR can be measured directly or derived from the PDD data. - CORRECT
ANSWERS True
(T/F) In general TAR increases with increase in depth. - CORRECT ANSWERS False
(T/F) At orthovoltage beam quality's (>about 0.5 mm Cu HVL) BSF increases with an increase in
energy. - CORRECT ANSWERS False
(T/F) TAR decreases with increase in field size. - CORRECT ANSWERS False
(T/F) Exit dose calculated using the standard PDD tables would give the correct exit dose. -
CORRECT ANSWERS False
,(T/F) The off axis ratio is the dose at any point in a plane perpendicular to the central axis to that
of the dose on the central axis in that plane. - CORRECT ANSWERS True
(T/F) At a phantom depth of 10 cm, on the central axis, scatter contribution to the dose is more
for an accelerator photon beam compared to a Co-60 beam. - CORRECT ANSWERS False
(T/F) At any depth, the scatter contribution to total dose decreases with increase in incident
photon energy - CORRECT ANSWERS True
(T/F) Cross-beam profile can give information regarding field size, physical penumbra, beam
flatness, and symmetry. - CORRECT ANSWERS True
(T/F) A wedge in motion is known as a dynamic wedge. - CORRECT ANSWERS False
(T/F) The energy fluence of the photons falls according to the inverse square law of distance
with the source position as the origin. - CORRECT ANSWERS True
(T/F) Photon beams have a finite range in a patient. - CORRECT ANSWERS False
(T/F) In the AAPM TG-51 protocol, the electron beam quality is specified by E0 , the mean
energy of the electrons incident on the patient. - CORRECT ANSWERS False
(T/F) The field size dependence of the PDD of an accelerator photon beam is very much
influenced by the electron contamination of the beam - CORRECT ANSWERS True
(T/F) Scatter generally decreases PDD. - CORRECT ANSWERS False
,(T/F) Half blocked tangential breast treatments can be easily accomplished with independent
jaw movements. - CORRECT ANSWERS True
(T/F) One of the advantages of a dynamic wedge over a physical wedge for treatment is that
there is no change in beam quality across the field size. - CORRECT ANSWERS True
(T/F) The tail of the electron beam depth dose distribution is due to some long-range electrons
in the beam. - CORRECT ANSWERS False
(T/F) Electron beams have a finite range in medium. - CORRECT ANSWERS True
(T/F) Low-energy electrons are more easily scattered compared to high-energy electrons. -
CORRECT ANSWERS True
The beam output (cGy/min) measured in air for a Co-60 unit increases with field size mainly due
to:
collimator scatter
room scatter
couch backscatter
chamber wall scatter - CORRECT ANSWERS collimator scatter
Disadvantages of using a physical wedge include:
hardening of the beam, which also depends on wedge thickness
difficulty in positioning the wedge reproducibly in the beam path
, attenuation of the beam and an increase in treatment time
inconvenience in handling heavy wedges - CORRECT ANSWERS hardening of the beam,
which also depends on wedge thickness
attenuation of the beam and an increase in treatment time
inconvenience in handling heavy wedges
In case of isocentric treatment, compared to constant SSD method:
set-up time decreases
set-up error decreases
treatment accuracy increases
overall time to treat a patient increases - CORRECT ANSWERS set-up time decreases
set-up error decreases
treatment accuracy increases
The TAR:
concept is usually not preferred with accelerator photon beams because the dose in free air is
not well defined for these beams
can be derived from PDD data
