ABR ABR Radiation Dosimetry 2

Question 1

What phantom material is required for reference dosimetry measurements per TG-51?

Accepted Answer

Liquid water

Answer

TG-51 requires measurements in a liquid water phantom as it is the reference medium for absorbed dose-to-water calibrations.

Question 2

Which of the following best describes the percent depth dose (PDD) curve for a megavoltage photon beam?

Accepted Answer

Builds up to a maximum then exponentially decreases

Answer

Megavoltage photon beams exhibit a skin-sparing buildup region before reaching dose maximum (dmax), after which dose decreases with depth due to attenuation.

Question 3

What is the tissue-phantom ratio (TPR) used to characterize in radiation dosimetry?

Accepted Answer

Beam quality and off-axis output factors

Answer

The tissue-phantom ratio (TPR) characterizes beam quality and is used to calculate output factors independent of the inverse square law.

Question 4

In electron beam dosimetry, what is the recommended reference depth for calibration per TG-51?

Accepted Answer

dref = 0.6·R50 – 0.1 cm

Answer

For electron beams, TG-51 specifies calibration at dref = 0.6·R50 − 0.1 cm, where R50 is the depth of 50% ionization.

Question 5

What is the primary purpose of a farmer chamber's graphite wall in dosimetry?

Accepted Answer

To provide charged particle equilibrium

Answer

The graphite wall of a Farmer chamber helps establish charged particle equilibrium and has a water-equivalent mass to minimize perturbation.

ABR - American Board of Radiology Medical Physics Exam Practice Test

ABR - American Board of Radiology Medical Physics Exam Practice Test

ABR ABR Radiation Dosimetry 2