X-Ray Certification Radiobiology 1 — Questions and Answers
Question 1: What process occurs when radiation removes electrons from atoms, creating ion pairs that can damage biological molecules?
- Fluorescence
- Ionization (Correct answer)
- Excitation
- Photoelectric absorption
Correct answer: Ionization
Ionization is the process by which radiation removes electrons from atoms, creating charged ion pairs that can disrupt biological molecules such as DNA.
Question 2: Which phase of the cell cycle is considered most radiosensitive?
- S phase (DNA synthesis)
- G1 phase (post-mitotic gap)
- M phase (mitosis) (Correct answer)
- G2 phase (pre-mitotic gap)
Correct answer: M phase (mitosis)
Cells in M phase (mitosis) are most radiosensitive because chromosomes are condensed and there is minimal time for DNA repair before division occurs.
Question 3: Which law states that the most radiosensitive cells are those that are rapidly dividing and least differentiated?
- Inverse square law
- Ohm's law
- Bergonié-Tribondeau law (Correct answer)
- Beer-Lambert law
Correct answer: Bergonié-Tribondeau law
The Bergonié-Tribondeau law states that radiosensitivity is directly proportional to reproductive activity and inversely proportional to the degree of differentiation.
Question 4: What is the primary target molecule for radiation-induced biological damage in human cells?
- RNA
- Cell membrane lipids
- Mitochondria
- DNA (Correct answer)
Correct answer: DNA
DNA is the critical target molecule because damage to the genetic code can result in cell death, mutation, or carcinogenesis that cannot be easily repaired.
Question 5: Which organ system is considered most radiosensitive in the human body?
- Nervous system
- Muscle tissue
- Hematopoietic (blood-forming) system (Correct answer)
- Skeletal system
Correct answer: Hematopoietic (blood-forming) system
The hematopoietic system is most radiosensitive because bone marrow stem cells are rapidly dividing and undifferentiated, satisfying the Bergonié-Tribondeau criteria.
Question 6: What type of radiation effect increases in probability (not severity) with increasing dose and has no threshold?
- Deterministic effects
- Stochastic effects (Correct answer)
- Acute somatic effects
- Threshold effects
Correct answer: Stochastic effects
Stochastic effects such as cancer increase in probability with dose but the severity remains constant; no safe threshold dose exists below which they cannot occur.
Question 7: What is the approximate LD50/30 for humans exposed to whole-body radiation without medical support?
- 0.25–0.5 Gy
- 1–2 Gy
- 3–4 Gy (Correct answer)
- 10–15 Gy
Correct answer: 3–4 Gy
The LD50/30 (dose lethal to 50% of an exposed population within 30 days) for humans is approximately 3–4 Gy of whole-body radiation without medical intervention.
X-Ray Certification Radiobiology 1
What process occurs when radiation removes electrons from atoms, creating ion pairs that can damage biological molecules?