MDCB EXAM| 1021 QUESTIONS WITH
100% CORRECT ANSWERS
(T/F) In SAD techniques, the beams are weighted at dmax point. - ANSWER-False
(T/F) In SAD techniques, the beams are weighted at target center. - ANSWER-False
(T/F) Isodose or PDD data can be used directly for a patient, without any modification. -
ANSWER-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 - ANSWER-True
(T/F) TAR can be measured directly or derived from the PDD data. - ANSWER-True
(T/F) In general TAR increases with increase in depth. - ANSWER-False
(T/F) At orthovoltage beam quality's (>about 0.5 mm Cu HVL) BSF increases with an
increase in energy. - ANSWER-False
(T/F) TAR decreases with increase in field size. - ANSWER-False
(T/F) Exit dose calculated using the standard PDD tables would give the correct exit
dose. - ANSWER-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. - ANSWER-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. - ANSWER-False
(T/F) At any depth, the scatter contribution to total dose decreases with increase in
incident photon energy - ANSWER-True
(T/F) Cross‐beam profile can give information regarding field size, physical penumbra,
beam flatness, and symmetry. - ANSWER-True
(T/F) A wedge in motion is known as a dynamic wedge. - ANSWER-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. - ANSWER-True
(T/F) Photon beams have a finite range in a patient. - ANSWER-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. - ANSWER-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 - ANSWER-True
(T/F) Scatter generally decreases PDD. - ANSWER-False
(T/F) Half blocked tangential breast treatments can be easily accomplished with
independent jaw movements. - ANSWER-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. - ANSWER-True
(T/F) The tail of the electron beam depth dose distribution is due to some long‐range
electrons in the beam. - ANSWER-False
(T/F) Electron beams have a finite range in medium. - ANSWER-True
(T/F) Low‐energy electrons are more easily scattered compared to high‐energy
electrons. - ANSWER-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 - ANSWER-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 - ANSWER-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 - ANSWER-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
at dmax and PSF are practically the same quantity
always increases with depth - ANSWER-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
at dmax and PSF are practically the same quantity
The side of an equivalent square of a rectangular field (a cm x b cm) is approximately:
2ab/a+b
sqrt(ab)
(a+b)/2
none of the above - ANSWER-2ab/a+b
TMR depends on:
depth
field size
beam quality
SSD - ANSWER-depth
field size
beam quality
Collimator scatter Sc( r ), provides the:
output factor in air
influence of head scatter on beam output, with increasing collimator field size
influence of phantom scatter on beam output, with increasing collimator field size
, The mean energy of the electron beam, E0, can be determined, fairly accurately, from
the parameter:
2.33 R50
3 R50
R50
2 R50 - ANSWER-2.33 R50
According to the AAPM protocol, TG 51, the reference depth (in water) for electron
beam calibration, is given (in cm) by:
0.6 R50
0.6 R50 - 0.1
0.5 R50
Dmax - ANSWER-0.6 R50 - 0.1
The surface dose for clinical electron beam is:
about 75% to 95%
about 40% to 70%
less than 40%
none of these values - ANSWER-about 75% to 95%
none of the above - ANSWER-output factor in air
influence of head scatter on beam output, with increasing collimator field size
When utilizing an SSD technique, the:
patient is set up with respect to the patient skin at constant SSD
patient is set up with respect to the target center at constant SAD
concept of PDD is used to determine the dose at the input port
concept of TAR is used to determine the dose at the input port - ANSWER-patient is set
up with respect to the patient skin at constant SSD
concept of PDD is used to determine the dose at the input port
The depth of dose maximum in a patient for a relatively clean Co‐60 beam is:
0 mm or skin surface
5 mm
5 cm
none of the above - ANSWER-5 mm
What is the recommended depth for accelerator photon beam calibration?
0 mm or phantom surface
100% CORRECT ANSWERS
(T/F) In SAD techniques, the beams are weighted at dmax point. - ANSWER-False
(T/F) In SAD techniques, the beams are weighted at target center. - ANSWER-False
(T/F) Isodose or PDD data can be used directly for a patient, without any modification. -
ANSWER-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 - ANSWER-True
(T/F) TAR can be measured directly or derived from the PDD data. - ANSWER-True
(T/F) In general TAR increases with increase in depth. - ANSWER-False
(T/F) At orthovoltage beam quality's (>about 0.5 mm Cu HVL) BSF increases with an
increase in energy. - ANSWER-False
(T/F) TAR decreases with increase in field size. - ANSWER-False
(T/F) Exit dose calculated using the standard PDD tables would give the correct exit
dose. - ANSWER-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. - ANSWER-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. - ANSWER-False
(T/F) At any depth, the scatter contribution to total dose decreases with increase in
incident photon energy - ANSWER-True
(T/F) Cross‐beam profile can give information regarding field size, physical penumbra,
beam flatness, and symmetry. - ANSWER-True
(T/F) A wedge in motion is known as a dynamic wedge. - ANSWER-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. - ANSWER-True
(T/F) Photon beams have a finite range in a patient. - ANSWER-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. - ANSWER-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 - ANSWER-True
(T/F) Scatter generally decreases PDD. - ANSWER-False
(T/F) Half blocked tangential breast treatments can be easily accomplished with
independent jaw movements. - ANSWER-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. - ANSWER-True
(T/F) The tail of the electron beam depth dose distribution is due to some long‐range
electrons in the beam. - ANSWER-False
(T/F) Electron beams have a finite range in medium. - ANSWER-True
(T/F) Low‐energy electrons are more easily scattered compared to high‐energy
electrons. - ANSWER-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 - ANSWER-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 - ANSWER-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 - ANSWER-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
at dmax and PSF are practically the same quantity
always increases with depth - ANSWER-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
at dmax and PSF are practically the same quantity
The side of an equivalent square of a rectangular field (a cm x b cm) is approximately:
2ab/a+b
sqrt(ab)
(a+b)/2
none of the above - ANSWER-2ab/a+b
TMR depends on:
depth
field size
beam quality
SSD - ANSWER-depth
field size
beam quality
Collimator scatter Sc( r ), provides the:
output factor in air
influence of head scatter on beam output, with increasing collimator field size
influence of phantom scatter on beam output, with increasing collimator field size
, The mean energy of the electron beam, E0, can be determined, fairly accurately, from
the parameter:
2.33 R50
3 R50
R50
2 R50 - ANSWER-2.33 R50
According to the AAPM protocol, TG 51, the reference depth (in water) for electron
beam calibration, is given (in cm) by:
0.6 R50
0.6 R50 - 0.1
0.5 R50
Dmax - ANSWER-0.6 R50 - 0.1
The surface dose for clinical electron beam is:
about 75% to 95%
about 40% to 70%
less than 40%
none of these values - ANSWER-about 75% to 95%
none of the above - ANSWER-output factor in air
influence of head scatter on beam output, with increasing collimator field size
When utilizing an SSD technique, the:
patient is set up with respect to the patient skin at constant SSD
patient is set up with respect to the target center at constant SAD
concept of PDD is used to determine the dose at the input port
concept of TAR is used to determine the dose at the input port - ANSWER-patient is set
up with respect to the patient skin at constant SSD
concept of PDD is used to determine the dose at the input port
The depth of dose maximum in a patient for a relatively clean Co‐60 beam is:
0 mm or skin surface
5 mm
5 cm
none of the above - ANSWER-5 mm
What is the recommended depth for accelerator photon beam calibration?
0 mm or phantom surface
