Biological Effects of X-ray Radiation
M1 ORA/MISTRAL
117
C Biological Effects of X-ray Radiation
(Extract from www.princeton.edu/main/)
Mechanisms of damage
Injury to living tissue results from the transfer of energy to atoms and molecules in the cellular
structure. Ionizing radiation causes atoms and molecules to become ionized or excited. These
excitations and ionizations can:
produce free radicals
break chemical bonds
produce new chemical bonds and cross-linkage between macromolecules
damage molecules that regulate vital cell processes (e.g. DNA, RNA, proteins)
The cell can repair certain levels of cell damage. At low doses, such as that received every day
from background radiation, cellular damage is rapidly repaired.
At higher levels, cell death results. At extremely high doses, cells cannot be replaced quickly
enough, and tissues fail to function.
Tissue sensitivity
In general, the radiation sensitivity of a tissue is:
proportional to the rate of proliferation of its cells
inversely proportional to the degree of cell differentiation
For example, the following tissues and organs are listed from most radiosensitive to least
radiosensitive:
Most sensitive:
Blood-forming organs
Reproductive organs
Skin
Bone and teeth
Muscles
Least sensitive:
Nervous system
This also means that a developing embryo is most sensitive to radiation during the early stages of
differentiation, and an embryo/fetus is more sensitive to radiation exposure in the
first
trimester
than in later trimesters.
Prompt and delayed effects
Radiation effects can be categorized by
when
they appear.
Prompt effects: effects, including radiation sickness and radiation burns, seen immediately
after large doses of radiation delivered over short periods of time.
