Dan Test #3

LET

a measure of the rate at which energy is transferred from ionizing radiation and tissue

unit of LET

KeV/microm

the ability of ionizing rad to produce a biologic response increases as the LET of radiation _____

increases

LET of diagnostic x-radiation

3KeV/microm

which have low LET: xray, gamma, alpha, neutrons

xray, gamma

RBE

expresses the relative effectiveness of radiations w differing LETs in producing a given biological effect

OER

the ratio of dose without O2 supplied to dose under normal conditions

under anoxic conditions, a ___ dose is required to produce a given effect

higher

in vitro

outside the body or outside the cell

in vivo

macromolecules inside the living cell

radiation effects on protein

disruption of protein structure, inactivation of enzymes

radiation effects of lipids

may be converted to peroxides (poisonous to cell)

radiation effects of carbohydrates

chain degradation (no fuel for metabolism)

radiation effects of nucleic acids

DNA, directs function of the cell

most radiosensitive molecule

DNA

low LET radiation

primary indirect effect

single strand breaks to DNA

DNA usually recovers

genetic effect “point mutation”

high LET radiation

directly effects DNA molecules

double strand breaks

cross linking

cell death

cancer

does high or low LET radiation have double strand breaks

high

chromosomal abberation

unrepaired damage to chromosome (chromatid) that results in mutation

restitution

breaks in chromosome (chromatid) rejoin into their normal configuration

direct action

the initial ionizing event occurs on target molecule

direct action is more likely with high or low LET

high

indirect action

initial ionizing event occurs on a distant, noncritical molecule that transfers the energy of ion to the target molecule

the principle action of radiation on humans is indirect or direct

indirect

dissociation of H20 into other molecular products when it is irradiated

radiolysis

reactions that may occur following ionization

ion pair may rejoin into a stable h20 molecule (no biologic damage)

negative ion may attach to another h20 molecule to form a 3rd type of ion

end result of the radiolysis of h20

formation of an ion pair: H+ & OH-

two free radicals: H ** and OH* \*

free radical

uncharged molecule with a single valence electron

OH \* free radicals can bond to form

hydrogen peroxides

H\* free radical can bone with molecule O2(O2) to form

hydroperoxyl radical

primary damaging by products of the radiolysis of H20

hydrogen peroxide and the hydroperoxyl free radicals

period of DNA synthesis between cell division

interphase

3 stages of interphase

G1, S, G2

period of cell grown and protein synthesis

G1

cell duplicates its DNA

S

cell resumes normal growth before division

G2

cells are most sensitive during

mitosis (M)

resistance is usually greatest during which phase

late S phase

radiosensitivity is ____ ____ to reproductive activity

direction proportional

radiosensitivity is ______ to the cells degree of differentiation

indirectly proportional

as a cell ages and becomes more specialized, it becomes more or less radioresistant

more

cells are most radiosensitive when they are

immature, undifferentiated

highest radiosensitivity

skin, blood, intestinal crypt cells, reproductive (Germ(

lowest radiosensitivity

brain cells, muscle cells

instant death at ___ Gy of exposure

1000Gy

reproductive death at ___ GY of exposure

1-10

interphase death, programmed cell death

apoptosis

uncontrolled rapid proliferation of cells

carcinogenesis

most common stochastic effect

cancer

malignant effects to offspring (progeny) from irradiation of sperm/ova prior to conception

mutagenesis

which disease has the shortest latent period

leukemia

cancer of the blood or blood marrow

leukemia

radiolysis of water can form

free radicals

hydrogen peroxide