Mosby QA Flashcards
The mathematical correction for the effect of temperature and pressure on ionization is based on a standardized barometric pressure of:
The correction is based on barometric pressure of 760 mm Hg.
Which of the following is true regarding beam filtration?
Beam filtration removes lower energy photons, making the beam “harder” due to an increased proportion of high-energy photons.
The rationale for using a half-beam block in a treatment field is based on:
A. the absence of beam divergence at the central axis B. the reduction of scatter dose at the central axis C. the increased accuracy of dose calculation at the central axis D. the depth of Dmax increased due to the block
There is no beam divergence at the central axis. Thus, the half-beam block creates a sharp field edge with no divergence.
How many atoms are in one gram atomic weight of I-125?
The number of atoms in one gram atomic weight is given by Avogadro’s number (6.0228 x 1023). Dividing this number by the gram atomic weight of any element will give the number of atoms per gram atomic weight.
4.81 x 10^21 atoms
Which of the following radiation measuring devices is appropriate for verifying dose calculations in specific areas of a treated field?
A. ion chamber
B. film badge
C. pocket dosimeter
D. thermoluminescent dosimeter
thermoluminescent dosimeter (TLDs are most appropriate for verifying dose in tissue since the lithium fluoride crystals absorb radiation similar to tissue.)
If heavy charged particles have a quality factor (Q) of 20, what is the absorbed dose equivalent for 100 cGy?
A. 10 Sv
B. 2 Sv
C. 2000 Sv
D. 20 Sv
D. 20 Sv
1 sievert (Sv) is equal to 1 Gy. The absorbed dose equivalent is found by multiplying Q by the absorbed dose.
Light field and radiation field congruence should be checked:
According to AAPM Task Group 40, light field and radiation field congruence should be checked monthly.
The three basic principles that guide radiation protection are:
In order to keep exposures low, three basic principles should be followed: limit time, increase distance, and shield from exposure.
The room temperature is 21.5°C, and the barometric pressure is 745mmHg. Calculate the temperature and pressure correction.
A. 1.018
Formula needed Use the correction formula ((273.2+T)/295.2)) x (760/P).
Which theory of radiation interaction is illustrated by the operating principles of an ionization chamber?
Bragg-Gray cavity theory states that ionization in an air cavity can be related to ionization in a medium.
Which of the following should be checked on a linac daily?
A. light/radiation field coincidence
B. beam flatness and symmetry
C. field size indicators
D. none of the above
D. none of the above
All of the above parameters are to be checked monthly.
Which is not true of the electromagnetic spectrum? All photons in the spectrum have the same:
A. velocity
B. energy
C. mass
D. charge
B. energy
Notes: All photons in the spectrum have the same velocity, mass, and charge—none.
Which of the following best describes an isodose curve?
A. Points within the patient receiving the same dose are joined together forming a curve. B. Points on the patient's skin surface receiving dose relative to Dmax are connected forming a curve. C. Points within the patient receiving the same dose equidistant from the maximum dose point are joined together forming a curve. D. none of the above
A. Points within the patient receiving the same dose are joined together forming a curve.
Notes: Several dose points of the same value are joined together forming a curve. The curve can be specified in either absolute dose or dose relative to the maximum dose in the treatment plan.
The probability of bremsstrahlung production:
A. decreases with atomic number
B. increases with atomic number
C. is independent of atomic number
D. decreases with the square of the atomic number
B. Increase with atomic number
Obliquely incident photon beams that “flash” over the patient surface such as in the treatment of a chestwall can result in:
A. increasing of the skin sparing effect
B. inaccurate dose delivery
C. neutron dose scatter to the patient
D. decrease of the skin-sparing effect
D. decrease of the skin-sparing effect
Notes: Obliquely incident photon beams that “flash” over the patient surface, such as in treating a chestwall, can shift the depth of Dmax closer to the skin surface, resulting in a reduction of the skin sparing effect.
