Morgan Community College – Radiology Program RTE 2031 Radiation Biology – Chapter 30 Outline

Vocabulary flashcards covering key terms from Radiation Biology Chapter 30 Outline.

Bergonié and Tribondeau law

Radiosensitivity increases with metabolic and maturation rate; stem (immature) cells are more radiosensitive than mature cells; younger tissue and organs are more radiosensitive; high metabolic activity and rapid cell division (e.g., embryonic/fetal cells) contribute; examples include intestinal lining, gonads, bone marrow.

Stem cells

Immature, undifferentiated precursor or blast cells; more radiosensitive than mature cells.

Immature cells

Stem/precursor cells that are more radiosensitive than mature cells.

Younger tissue

Tissue and organs that are still developing tend to be more radiosensitive.

Metabolic activity

Higher metabolic activity increases radiosensitivity; examples include intestinal lining, gonads, and bone marrow.

Rapidly dividing cells

Cells that divide quickly are more radiosensitive (e.g., embryonic/fetal cells).

Linear Energy Transfer (LET)

Rate of energy transfer from ionizing radiation to soft tissue; higher LET causes greater tissue damage; unit: keV/μm.

Diagnostic x-rays LET

Approximately 3 keV/μm.

High LET

Alpha particles, protons, neutrons; cause greater tissue damage per unit dose.

Low LET

Electrons, positrons, gamma rays, x-rays; cause less damage per unit dose.

Radiation weighting factor

Factor assigned to radiation types based on LET to account for differing biological effectiveness.

Relative Biologic Effectiveness (RBE)

Compares biological damage from different radiations relative to diagnostic x‑rays.

RBE formula

RBE = Test dose to produce same effect / Standard dose to produce effect.

RBE = 1 for diagnostic x‑rays

Diagnostic x‑rays have an RBE of 1.

LET vs RBE relationship

Higher LET generally yields higher RBE up to a cell death threshold.

Protraction

Continuous, low-dose delivery of radiation.

Fractionation

Delivery of dose in smaller portions over several days.

Oxygen Effect (OER)

Radiosensitivity increases with oxygenation; OER = Dose under aerobic conditions / Dose under anoxic conditions.

OER and LET relationship

OER increases as LET is low; OER decreases as LET becomes high (inverse relationship).

Age and radiosensitivity

Embryo/fetus are highly radiosensitive; sensitivity decreases with maturity; elderly may show increased sensitivity due to slower repair.

Cell Recovery

Repair and repopulation of healthy cells; interphase death occurs when a cell dies before replication.

Radiosensitizers

Chemical agents that enhance radiosensitivity.

Radioprotective agents

Chemical agents that protect cells from radiation; limited clinical use due to toxicity.

Hormesis

Belief that low-dose radiation may stimulate protective biological responses.

Dose–Response relationships

Framework to predict biological effects; two main categories: deterministic and stochastic effects.

Deterministic effects

High-dose, early response with a threshold; severity increases with dose (e.g., skin reddening, burns, cataracts).

Stochastic effects

Low-dose, late response with no threshold; probability increases with dose (e.g., cancer, leukemia, genetic effects).

Linear vs Non-linear dose‑response

Linear: proportional response with dose; non-linear: non-proportional, curved relationship.

Threshold vs Non-threshold

Threshold: effect occurs only above a certain dose; non-threshold: any dose carries some probability of effect.

Diagnostic Radiology extrapolation model

Extending a dose–response curve beyond measured data; often assumes linear, non-threshold model for late effects.

100 mGy threshold claim

No observed human radiation responses after doses less than 100 mGy.