Biological Effects of Radiation Flashcards

The oxygen enhancement ratio (OER) for low-LET radiation is approximately:

Answer: 2.5–3.0

For low-LET radiation such as X-rays and gamma rays, the OER is approximately 2.5–3.0, meaning hypoxic cells require 2.5–3 times more dose to achieve the same level of killing as well-oxygenated cells.

Which of the following radiation-induced chromosome aberrations is considered an 'unstable' aberration that is eliminated from the dividing cell population over time?

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.

The latency period for radiation-induced solid tumors in humans is typically:

Answer: 5–10 years or more

Radiation-induced solid tumors typically have a latency period of at least 5–10 years, with many tumors appearing decades after exposure, as seen in atomic bomb survivor data.

Which model best describes the relationship between radiation dose and cancer risk at low doses used in current radiation protection?

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.

Radiation-induced cataracts are classified as:

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 2–10 Gy.

Which of the following correctly lists tissues in order from MOST to LEAST radiosensitive (for acute effects)?

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.

In the linear-quadratic (LQ) model, the α/β ratio for early-responding normal tissues is typically:

Answer: 8–12 Gy

Early-responding tissues (high α/β ~8–12 Gy) show a more linear dose-response and less sparing with fractionation, while late-responding tissues have low α/β (~1–3 Gy).