Radiation Health and Safety Test Radiation Biology & Health Effects 2 — Questions and Answers
Question 1: Deterministic (tissue) radiation effects are characterized by which dose-response relationship?
- Linear no-threshold (LNT) with no minimum dose
- A threshold below which effects do not occur, and severity increases above that threshold (Correct answer)
- A hormetic response where low doses are beneficial
- A random probability of occurrence at any dose level
Correct answer: A threshold below which effects do not occur, and severity increases above that threshold
Deterministic effects have a threshold dose; below it, no effect is observed, but above it, effect severity increases with dose as more cells are killed.
Question 2: Acute radiation syndrome (ARS) occurs after whole-body exposure generally above which dose range?
- 0.1 to 0.5 Gy
- 1 to 2 Gy (Correct answer)
- 5 to 10 Gy
- Greater than 20 Gy
Correct answer: 1 to 2 Gy
ARS typically begins to manifest clinically after whole-body doses of approximately 1–2 Gy, with the hematopoietic syndrome being the first to appear.
Question 3: The hematopoietic syndrome of ARS primarily results from damage to which organ system?
- Gastrointestinal tract lining
- Central nervous system
- Bone marrow and blood-forming cells (Correct answer)
- Skin and mucous membranes
Correct answer: Bone marrow and blood-forming cells
The hematopoietic syndrome is caused by destruction of bone marrow stem cells, leading to decreased production of red blood cells, white blood cells, and platelets.
Question 4: According to the Law of Bergonié and Tribondeau, cells are most sensitive to radiation when they are:
- Highly differentiated and non-dividing
- Undifferentiated and rapidly dividing (Correct answer)
- Large and metabolically inactive
- In the G1 phase only
Correct answer: Undifferentiated and rapidly dividing
Bergonié and Tribondeau established that cells are more radiosensitive when they are undifferentiated (immature) and have a high mitotic rate.
Question 5: Which phase of the cell cycle is generally considered the most radiosensitive?
- G1 (post-mitotic gap)
- S phase (DNA synthesis)
- G2/M (late gap and mitosis) (Correct answer)
- G0 (resting phase)
Correct answer: G2/M (late gap and mitosis)
Cells in G2 and M phase are most radiosensitive because DNA repair mechanisms are suppressed during mitosis and damage cannot be repaired before division.
Question 6: The relative biological effectiveness (RBE) compares the biological damage of a test radiation to that of:
- Alpha particles at 5 MeV
- 250 kVp X-rays as the reference radiation (Correct answer)
- Thermal neutrons at 0.025 eV
- Co-60 gamma rays at 1.25 MeV
Correct answer: 250 kVp X-rays as the reference radiation
RBE is defined as the ratio of the dose of 250 kVp X-rays to the dose of the test radiation needed to produce the same biological effect.
Question 7: Radiation-induced cataracts are classified as which type of radiation effect?
- Stochastic with no threshold
- Deterministic with a threshold dose (Correct answer)
- Hereditary genetic effect
- Teratogenic effect only in utero
Correct answer: Deterministic with a threshold dose
Cataracts are a deterministic (tissue reaction) effect with a threshold; the current ICRP threshold estimate is approximately 0.5 Gy for protracted exposure.
Radiation Health and Safety Test Radiation Biology & Health Effects 2
Deterministic (tissue) radiation effects are characterized by which dose-response relationship?