CHP Biological Effects of Radiation 3 β Questions and Answers
Question 1: The oxygen enhancement ratio (OER) for low-LET radiation is approximately:
- 1.0 (no enhancement)
- 1.5
- 2.5β3.0 (Correct answer)
- 5.0β6.0
Correct answer: 2.5β3.0
For low-LET radiation such as X-rays and gamma rays, the OER is approximately 2.5β3.0, meaning hypoxic cells require 2.5β3 times more dose to achieve the same level of killing as well-oxygenated cells.
Question 2: Which of the following radiation-induced chromosome aberrations is considered an 'unstable' aberration that is eliminated from the dividing cell population over time?
- Reciprocal translocation
- Inversion
- Dicentic chromosome (Correct answer)
- Insertion
Correct answer: Dicentic chromosome
Dicentric chromosomes are unstable aberrations because they cause problems during cell division (bridge-breakage-fusion cycles), leading to cell death and their loss from the proliferating population over time.
Question 3: The latency period for radiation-induced solid tumors in humans is typically:
- Days to weeks
- Months to 1β2 years
- 5β10 years or more (Correct answer)
- 30β40 years only
Correct answer: 5β10 years or more
Radiation-induced solid tumors typically have a latency period of at least 5β10 years, with many tumors appearing decades after exposure, as seen in atomic bomb survivor data.
Question 4: Which model best describes the relationship between radiation dose and cancer risk at low doses used in current radiation protection?
- Threshold model β no risk below a specific dose
- Linear-quadratic model extrapolated to zero (LNT) (Correct answer)
- Hormesis model β low doses are beneficial
- Supralinear model β low doses are more dangerous per unit than high doses
Correct answer: Linear-quadratic model extrapolated to zero (LNT)
The linear no-threshold (LNT) model, derived from the linear-quadratic fit at high doses, is the basis of current radiation protection and assumes cancer risk is proportional to dose with no safe threshold.
Question 5: Radiation-induced cataracts are classified as:
- Stochastic effects with no threshold
- Deterministic effects occurring at doses above a threshold, now revised downward to ~0.5 Gy (Correct answer)
- Purely hereditary effects
- Deterministic effects requiring at least 5 Gy acute dose
Correct answer: Deterministic effects occurring at doses above a threshold, now revised downward to ~0.5 Gy
Cataracts are deterministic effects; ICRP now recognizes a threshold of approximately 0.5 Gy acute dose (or equivalent fractionated dose), revised downward from the previously assumed 2β10 Gy.
Question 6: Which of the following correctly lists tissues in order from MOST to LEAST radiosensitive (for acute effects)?
- Bone marrow > intestinal epithelium > liver > muscle (Correct answer)
- Muscle > liver > bone marrow > intestinal epithelium
- Intestinal epithelium > bone marrow > liver > muscle
- Liver > intestinal epithelium > muscle > bone marrow
Correct answer: Bone marrow > intestinal epithelium > liver > muscle
Rapidly dividing tissues are most radiosensitive: bone marrow and intestinal epithelium are highly sensitive, while liver is intermediate and muscle is highly radioresistant.
Question 7: In the linear-quadratic (LQ) model, the Ξ±/Ξ² ratio for early-responding normal tissues is typically:
- 1β3 Gy
- 8β12 Gy (Correct answer)
- 20β30 Gy
- 0.1β0.5 Gy
Correct answer: 8β12 Gy
Early-responding tissues (high Ξ±/Ξ² ~8β12 Gy) show a more linear dose-response and less sparing with fractionation, while late-responding tissues have low Ξ±/Ξ² (~1β3 Gy).
CHP Biological Effects of Radiation 3
The oxygen enhancement ratio (OER) for low-LET radiation is approximately: