ARRT Radiation Physics and Radiobiology 4 — Questions and Answers
Question 1: Which of the following is an example of deterministic (non-stochastic) radiation effect?
- Radiation-induced leukemia
- Cataracts from high-dose eye exposure (Correct answer)
- Heritable genetic mutations
- Solid tumor induction
Correct answer: Cataracts from high-dose eye exposure
Cataracts are a deterministic effect with a dose threshold; they occur in all exposed individuals once the threshold is exceeded, with severity increasing with dose.
Question 2: Pair production requires a minimum photon energy of:
- 0.511 MeV
- 1.02 MeV (Correct answer)
- 2.04 MeV
- 0.1 MeV
Correct answer: 1.02 MeV
Pair production requires at least 1.02 MeV (twice the rest-mass energy of an electron, 2 × 0.511 MeV) to create an electron-positron pair.
Question 3: What does the term 'radiolysis of water' describe?
- Water absorbing radiation without chemical change
- Ionization of water molecules by radiation producing free radicals (Correct answer)
- Reduction of hydrogen bonds in ice by radiation
- Activation of water as a radioprotector
Correct answer: Ionization of water molecules by radiation producing free radicals
Radiolysis of water is the decomposition of water molecules by ionizing radiation, producing reactive free radicals such as hydroxyl (·OH) and hydrogen (H·) radicals.
Question 4: The ALARA principle in radiation protection stands for:
- As Low As Reasonably Achievable (Correct answer)
- All Limits Are Reasonably Applicable
- Allowable Levels Are Regularly Assessed
- As Low As Radiation Allows
Correct answer: As Low As Reasonably Achievable
ALARA (As Low As Reasonably Achievable) is the guiding principle requiring radiation doses to be kept as low as possible while still achieving the diagnostic or therapeutic objective.
Question 5: Which type of chromosome aberration results from two simultaneous double-strand breaks in different chromosomes?
- Deletion
- Inversion
- Ring chromosome
- Translocation (Correct answer)
Correct answer: Translocation
Translocation results when double-strand breaks occur in two different chromosomes and the fragments rejoin incorrectly, exchanging segments between chromosomes.
Question 6: The effective dose equivalent (in sieverts) accounts for which of the following factors?
- Only the absorbed dose in gray
- Absorbed dose, radiation weighting factor, and tissue weighting factor (Correct answer)
- Physical half-life and biologic half-life
- Distance and time only
Correct answer: Absorbed dose, radiation weighting factor, and tissue weighting factor
Effective dose is calculated by multiplying the absorbed dose by the radiation weighting factor (for radiation type) and the tissue weighting factor (for organ sensitivity).
Question 7: In the linear no-threshold (LNT) model, which of the following is assumed?
- There is a safe threshold dose below which no cancer risk exists
- Cancer risk is proportional to dose with no safe threshold (Correct answer)
- High doses are proportionally less harmful than low doses
- Only acute doses cause stochastic effects
Correct answer: Cancer risk is proportional to dose with no safe threshold
The LNT model assumes that any radiation dose, no matter how small, carries some proportional risk of cancer induction, with no absolutely safe level.
ARRT Radiation Physics and Radiobiology 4
Which of the following is an example of deterministic (non-stochastic) radiation effect?