Biological Effects of Radiation Flashcards

Which of the following best describes the concept of 'relative biological effectiveness' (RBE)?

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.

The concept of 'fractionation' in radiation therapy exploits which biological principle?

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.

Which cell cycle phase is generally considered MOST radiosensitive?

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.

Radiation-induced genomic instability is best characterized as:

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.

The 'bystander effect' in radiation biology refers to:

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.

Which of the following organs has the LOWEST weighting factor (wT) in the ICRP radiation protection system?

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).

At very high doses (>10 Gy whole-body), the primary cause of death within hours to days is:

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.