1) Lesion at 1-cm depth in tissue is to be treated with 6-MeV electron beam with bolus. A dose of 1.5 Gy to 80% is prescribed. If output is 1cGy/MU, SSD is 104 cm and cone factor is 0.8, what should the thickness of the bolus be, and how many MU should be delivered?
A. 0 cm, 153 MU
B. 0 cm, 153 MU
C. 0 cm, 170 MU
D. 1 cm, 209 MU
E. 1 cm, 270 MU
2) Which of the following is true regarding geometric penumbra?
A. It increases as source diameter increases.
B. It decreases as SSD increases.
C. It is independent of source-collimator distance.
D. It decreases as depth increases.
E. All of the above are true
3) To achieve a standard deviation of 2%, _ counts must be collected.
A. 400
B. 1414
C. 2500
D. 10000
E. 40000
4) All of the following reduce resolution in positron emission tomography (PET) except:
A. Large size of the detector.
B. Range of positrons in tissue.
C. Organ motion during the scan.
D. Size of the focal spot.
5) Which parameter(s) change as a result of coherent scatter of a photon from an atom?
A. Wavelength.
B. Energy.
C. Direction of travel.
D. Electron configuration of the atom.
E. All of the above.
6) Which imaging modality would allow one to distinguish an artificial diamond made of zirconium oxide ZrO2 (zirconium has atomic number 40) from a natural one made of carbon atoms (atomic number 6)?
A. Ultrasound.
B. Diagnostic X-rays.
C. MRI
D. PET
E. None of the above.
7) Which of the following is not true regarding pair production?
A. The threshold photon energy is 0.511 MeV
B. An electron and a positron are produced in the interaction of a photon with a nucleus.
C. The positron annihilates with an electron producing two 0.511 MeV photons.
D. The probability of pair production increases with the incident photon energy.
8) The maximum number of photoelectrons produced in a photoelectric interaction by a single photon with incident energy of 150 keV is _.
A. 1
B. 5
C. 10
D. Any number, as long as the sum of individual electron energies is equal to 150 keV
E. None of the above.
9) The mass attenuation coefficients for most materials (except hydrogen) are similar when _ interactions predominate.
A. Photoelectric
B. Compton
C. Pair production
D. Photonuclear disintegration
10) A superficial x-ray treatment is prescribed with a 2 mm A1 filter. By mistake, a 1 mm filter is used All of the following will occur except:
A. Increased dose rate.
B. Increased dose for the same timer setting.
C. Decreased HVL
D. Increased PDD.