RAD BIO CH.7

Radiation Biology

branch of biology concerned with the effects of ionizing radiation on living things

Radiation Biology includes

-Sequence of events occurring after the absorption of energy from ionizing radiation

The injury to the living system that may be produced

• The action of the living system to make up for the consequences of this energy assimilation

Ionizing radiation

Damages living systems by ionizing the atoms compromising the molecular structure of these systems and do not bond properly in molecules

Transfer determinants

charge, mass, energy vary determining the extent to which different radiation modalities transfer energy into biologic tissue.

Linear Energy Transfer (LET)

amount of energy deposited by radiation per unit length of track, described in keV and is a very important factor in assessing potential tissue and organ radiation damage

Low-LET radiation

~X-ray and Gamma ray

~causes indirect damage to the cell when interacting with biologic tissue producing a free radical molecule

Low-LET radiation generally causes _ damage to DNA.

sub-lethal

High LET radiation includes particles that possess substantial:

mass and charge

High LET radiation

~alpha particles

• ions of heavy nuclei

• charged particles released from interactions between neutrons and atoms

• Low energy neutron

As LET increases, RBE ____

increases

Relative Biological Effectiveness (RBE)

measurement unit used to compare the biological effects of different tissues irradiated by different forms of radiation

Oxygen Enhancement Ratio (OER)

the ratio of the radiation dose required to cause a particular biologic response of cells or organisms in an oxygen-deprived environment to the radiation dose required to cause an identical response under normal oxygenated conditions

Molecular effect of Irradiation

any visible radiation damage starts at a molecular level that can impair cellular function and damage to the organ systems

Effects of irradiation on Somatic cells

If a sufficient number of somatic cells are affected by ionizing radiation the entire body process may be disrupted.

Effects of irradiation on Germ cells

if ionizing radiation damages the germ cells, the damage initially caused may pass to future generations in the form of genetic mutations

Direct Action of ionizing radiation on a cell

Affects DNA by directly interacting with the atoms of the DNA molecule causing a single-strand or double-strand break

Indirect Action of ionizing radiation on a cell

when ionizing radiation interacts with water molecules producing radicals that cause cell damage. Low-LET irradiation

When a mutation occurs due to ionizing radiation damage

it can cause a loss/change in a nitrogenous base, letting the healthy cells receive incorrect genetic information to one of the two daughter cells when the cell divides

Covalent cross-links

Chemical unions created between atoms by the single sharing of one or more pairs of electrons

Effects of Ionizing Radiation on Chromosomes

Large-scale structural changes in a chromosome produced by ionizing radiation may be as grave for the cell as are radiation-induced changes in DNA.

what are the consequences of structural changes to the cell within the nucleus

Broken-end rearrangement producing grossly misshaped chromosomes, but can also have no visible damage to the chromatids

master or key molecule

a molecule that maintains normal cell function that is believed to be present in every cell and is necessary for cell survival

target theory

may be used to explain cell death and nonfatal cell abnormalities

Effects of irradiation on the entire cell

Damage to the cell's nucleus can reveals itself as

Instant death

Reproductive death

Mitotic or genetic death

Mitotic delay

interference with function

apoptosis or interphase death

cell survival curve

method of displaying the sensitivity of a particular type of cell to radiation

Cell Radiosensitivity

As LET increases, radio sensitivity increases.

The more mature and specialized a cell, the less radiosensitive it is (ex: nerve cell)

True/False: increasing oxygen enhancements enhances cell radiosensitivity

True, by enhancing oxygen the biological tissue radiosensitivity is increased

The Law of Bergoine and Tribondeau states:

that the radiosensitivity of cells is directly proportional to their reproductive activity and inversely proportional to their degree of differentiation.

effects of ionizing radiation on human cells

equal doses of ionizing radiation produce different degrees of damage in other kinds of human cells due to the differences in radiosensitivity

the more mature a human cell is the

less sensitive it is to radiation

High LET occurs

due to the dense radiation concentration in one area resulting in less travel in tissue