RAPHEX COMPREHENSIVE QUESTIONS AND
ANSWERS SURE A+
✔✔The ____ in a medical linac generates the high power and short-duration pulses to
run the electron gun and the klystron.
A. power supply
B. modulator
C. magnetron
D. wave guide
E. accelerator tube - ✔✔B. modulator
✔✔If a flattening filter designed for a 6-MV beam is accidentally applied to a 15-MV
beam, the magnitude of the horns at max will __________ and the dose rate per pulse
will ___________compared to the use of the proper 15-MV flattening filter.
A. increase; increase
B. increase; decrease
C. increase; remain the same
D. decrease; increase
E. decrease; decrease - ✔✔D. decrease; increase. As the x-ray beam energy
increases, the fluence distribution will be more forward peaked. So,
higher-energy beams need thicker flattening filters. Therefore, if a 6-MV flattening filter
is used for the 15-MV beam, the magnitude of the horns will decrease due to insufficient
attenuation along the CAX relative to off-axis points, and the dose rate will increase due
to a
decreased filter thickness.
✔✔Arrange the following MV photon and MeV electron beams in order of greatest to
least electron current in the linac accelerating cavity for the same dose rate.
A. 9 MeV, 6 MV, 15 MV
B. 9 MeV, 15 MV, 6 MV
C. 6 MV, 9 MeV, 15 MV
D. 6 MV, 15 MV, 9 MeV
, E. 15 MV, 6 MV, 9 MeV - ✔✔D. 6 MV, 15 MV, 9 MeV. The efficiency of bremsstrahlung
x-ray production increases with both atomic number of the target and energy of the
electron beam. MeV is always more efficient than MV to make.
✔✔Which charged particle beam has the steepest distal dose gradient?
A. positron
B. electron
C. proton
D. alpha
E. carbon - ✔✔E. carbon
✔✔A 10-MeV photon undergoes Compton scatter. The minimum energy of the
scattered photon is equal to
A. 1.022 MeV
B. 0.511 MeV
C. 0.256 MeV
D. 0.128 MeV
E. 0.064 MeV - ✔✔C. 0.256 MeV. The energy of the scattered photon is minimal, 0.256
MeV, when it scatters backwards. (1/2 of 0.511 MeV I guess)
✔✔____________is the dominant photon interaction in human tissue from a photon
beam in the therapeutic treatment range of 4 to 25 MeV, and _________affects the
likelihood of an interaction.
A. Photoelectric effect; atomic number
B. Photoelectric effect; electron density
C. Compton scatter; atomic number
D. Compton scatter; electron density
E. Pair production; electron density - ✔✔D. Compton scatter; electron density. Compton
scatter is dominant in water for photon energies between 25 keV to 25 MeV and
depends on electron density. The photoelectric effect is dominant below 25 keV and is
proportional to Z^3 and 1/E^3
✔✔The ratio of mass attenuation coefficients (M/p) for lead and water, (м /р)рь /
(w/p)water, is______ at 0.1 MeV, at 1 MeV, and _at 10 MeV, respectively:
А . >1; >1;>1
B. >1; <1; >1
C. > 1;>1;<1
D. <1; >1; >1
E. >1; ~1; >1 - ✔✔E. >1; ~1; >1. The mass atten. coeff. is large for low energies and
high-atomic-number media bc of the predominance of photoelectric interactions. 1 MeV
is Compton range, the (H/p) of lead and water do not differ greatly, since Compton
interaction is independent of atomic number.
✔✔Exposure (X) refers to
A. ionization created in the patient due to charged particle irradiation, in C/kg
ANSWERS SURE A+
✔✔The ____ in a medical linac generates the high power and short-duration pulses to
run the electron gun and the klystron.
A. power supply
B. modulator
C. magnetron
D. wave guide
E. accelerator tube - ✔✔B. modulator
✔✔If a flattening filter designed for a 6-MV beam is accidentally applied to a 15-MV
beam, the magnitude of the horns at max will __________ and the dose rate per pulse
will ___________compared to the use of the proper 15-MV flattening filter.
A. increase; increase
B. increase; decrease
C. increase; remain the same
D. decrease; increase
E. decrease; decrease - ✔✔D. decrease; increase. As the x-ray beam energy
increases, the fluence distribution will be more forward peaked. So,
higher-energy beams need thicker flattening filters. Therefore, if a 6-MV flattening filter
is used for the 15-MV beam, the magnitude of the horns will decrease due to insufficient
attenuation along the CAX relative to off-axis points, and the dose rate will increase due
to a
decreased filter thickness.
✔✔Arrange the following MV photon and MeV electron beams in order of greatest to
least electron current in the linac accelerating cavity for the same dose rate.
A. 9 MeV, 6 MV, 15 MV
B. 9 MeV, 15 MV, 6 MV
C. 6 MV, 9 MeV, 15 MV
D. 6 MV, 15 MV, 9 MeV
, E. 15 MV, 6 MV, 9 MeV - ✔✔D. 6 MV, 15 MV, 9 MeV. The efficiency of bremsstrahlung
x-ray production increases with both atomic number of the target and energy of the
electron beam. MeV is always more efficient than MV to make.
✔✔Which charged particle beam has the steepest distal dose gradient?
A. positron
B. electron
C. proton
D. alpha
E. carbon - ✔✔E. carbon
✔✔A 10-MeV photon undergoes Compton scatter. The minimum energy of the
scattered photon is equal to
A. 1.022 MeV
B. 0.511 MeV
C. 0.256 MeV
D. 0.128 MeV
E. 0.064 MeV - ✔✔C. 0.256 MeV. The energy of the scattered photon is minimal, 0.256
MeV, when it scatters backwards. (1/2 of 0.511 MeV I guess)
✔✔____________is the dominant photon interaction in human tissue from a photon
beam in the therapeutic treatment range of 4 to 25 MeV, and _________affects the
likelihood of an interaction.
A. Photoelectric effect; atomic number
B. Photoelectric effect; electron density
C. Compton scatter; atomic number
D. Compton scatter; electron density
E. Pair production; electron density - ✔✔D. Compton scatter; electron density. Compton
scatter is dominant in water for photon energies between 25 keV to 25 MeV and
depends on electron density. The photoelectric effect is dominant below 25 keV and is
proportional to Z^3 and 1/E^3
✔✔The ratio of mass attenuation coefficients (M/p) for lead and water, (м /р)рь /
(w/p)water, is______ at 0.1 MeV, at 1 MeV, and _at 10 MeV, respectively:
А . >1; >1;>1
B. >1; <1; >1
C. > 1;>1;<1
D. <1; >1; >1
E. >1; ~1; >1 - ✔✔E. >1; ~1; >1. The mass atten. coeff. is large for low energies and
high-atomic-number media bc of the predominance of photoelectric interactions. 1 MeV
is Compton range, the (H/p) of lead and water do not differ greatly, since Compton
interaction is independent of atomic number.
✔✔Exposure (X) refers to
A. ionization created in the patient due to charged particle irradiation, in C/kg
