CHP Biological Effects of Radiation 2 — Questions and Answers
Question 1: Which of the following best describes the concept of 'relative biological effectiveness' (RBE)?
- The ratio of a reference radiation dose to the test radiation dose producing the same biological effect (Correct answer)
- The absolute dose required to kill 50% of a cell population
- The probability of cancer induction per unit dose of any radiation type
- The ratio of absorbed dose to equivalent dose for a given radiation type
Correct answer: The ratio of a reference radiation dose to the test radiation dose producing the same biological effect
RBE is defined as the ratio of the reference radiation dose (typically 250 kVp X-rays) to the test radiation dose needed to produce an identical biological endpoint.
Question 2: The concept of 'fractionation' in radiation therapy exploits which biological principle?
- Tumor cells have higher LET than normal cells
- Normal tissues repair sublethal damage more efficiently than tumors between dose fractions (Correct answer)
- Fractionation increases the total dose that can be delivered without limit
- Tumor hypoxia is eliminated by splitting the dose
Correct answer: Normal tissues repair sublethal damage more efficiently than tumors between dose fractions
Fractionation allows normal tissues to repair sublethal damage between fractions more effectively than tumors, improving the therapeutic ratio.
Question 3: Which cell cycle phase is generally considered MOST radiosensitive?
- S phase (DNA synthesis)
- G1 phase
- M phase (mitosis) (Correct answer)
- G0 phase (quiescent)
Correct answer: M phase (mitosis)
Cells in M phase (mitosis) are most radiosensitive because chromosomes are condensed and the mitotic spindle apparatus is particularly vulnerable to radiation damage.
Question 4: Radiation-induced genomic instability is best characterized as:
- Immediate chromosome breaks visible in the first cell division after irradiation
- Persistent elevation of mutation rate and chromosomal aberrations in descendant cells generations after irradiation (Correct answer)
- Instability confined only to directly irradiated cells
- A deterministic effect with a clear dose threshold
Correct answer: Persistent elevation of mutation rate and chromosomal aberrations in descendant cells generations after irradiation
Genomic instability manifests as a persistently elevated rate of mutations and chromosomal aberrations appearing in cell descendants many generations after the initial irradiation.
Question 5: The 'bystander effect' in radiation biology refers to:
- Protection of unirradiated cells by proximity to irradiated cells
- Biological damage occurring in cells not directly traversed by radiation but receiving signals from irradiated neighbors (Correct answer)
- Enhanced DNA repair in cells adjacent to a radiation source
- The shielding effect of outer cell layers on inner cells
Correct answer: Biological damage occurring in cells not directly traversed by radiation but receiving signals from irradiated neighbors
The bystander effect describes radiation-induced biological responses (damage, apoptosis, mutations) in cells that were not directly hit by radiation but received signals from neighboring irradiated cells.
Question 6: Which of the following organs has the LOWEST weighting factor (wT) in the ICRP radiation protection system?
- Lung
- Colon
- Brain (Correct answer)
- Bone marrow
Correct answer: Brain
The brain has a tissue weighting factor of 0.01 in ICRP Publication 103, reflecting its relatively low radiation sensitivity for cancer induction compared to organs like the lung (0.12) or colon (0.12).
Question 7: At very high doses (>10 Gy whole-body), the primary cause of death within hours to days is:
- Bone marrow failure leading to infection and hemorrhage
- Cardiovascular and central nervous system syndrome (Correct answer)
- Gastrointestinal syndrome with fluid loss
- Pulmonary fibrosis and respiratory failure
Correct answer: Cardiovascular and central nervous system syndrome
Doses above ~10 Gy cause cardiovascular and central nervous system (CV/CNS) syndrome characterized by hypotension, ataxia, and seizures leading to death within hours to days.
CHP Biological Effects of Radiation 2
Which of the following best describes the concept of 'relative biological effectiveness' (RBE)?