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Sherer Ch6

QuestionAnswer
determine extent to which different radiation modalities transfer energy into biologic tissue Charge, mass, & energy
Average energy deposited per unit length of track (path of ionizing radiation) Linear Energy Transfer
what is LET for diagnostic purposes estimated to be? 3keV/micron
assesses potential tissue and organ damage LET
x-rays & gamma rays have what kind of LET? low
what kind of radiation causes damage primarily through indirect action that involves production of free radicals low LET radiation
Includes particles that possess substantial mass and charge such as Alpha particle, ions of heavy nuclei, charged particles released from interactions between neutrons and atoms high LET radiation
Causes dense ionization along its length of track, more likely to interact with biologic tissue high LET
DNA more likely to be damaged by ____ LET radiation high
does high or low LET have a greater probability of interacting with DNA? high
what is highest concern when radionuclide implanted, ingested, injected, or inhaled Internal contamination
describes relative capabilities of radiation with differing LETs to produce a particular biologic reaction relative biologic effectiveness (RBE)
what is the oxygen effect? Biologic tissue is more sensitive to radiation when exposed in aerobic state than in anaerobic state
describes oxygen effect numerically Oxygen Enhancement Ratio (OER)
ratio of 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 OER
X-ray & gamma have OER of about what? 3.0
OER of high LET radiation is what? approximately = to 1
oxygen fixation hypothesis Presence of oxygen in biologic tissues makes damage produced by free radicals permanent
biologic damage occurs as a result of ionization of atoms on master, or key, molecules (DNA), which can cause the molecules to become inactive or functionally altered direct action
effects produced by reactive free radicals that are created by the interaction of radiation with water molecules indirect action
when is direct action more likely to occur after high LET
Direct action damage to macromolecules occurs from absorption of energy through what kind of interactions? photoelectric and Compton interactions
configuration of one or more atoms having an unpaired electron but no net electrical charge free radical
Produce chemical reactions and cause bio damage by transferring their excess energy to other molecules. Thereby either breaking chemical bonds or causing point lesions free radicals
APPX 2/3 of radiation-induced damage is believed to be ultimately cause by what? hydroxyl free radical OH*.
hydroxyl radical OH* may bond with another OH* and form this substance which is poisonous to cell hydrogen peroxide (H2O2)
When free radicals act on DNA, ionizing radiation is _____ cause of damage indirect
ionizing radiation breaks DNA chemical bond or sugar-phosphate chain side rails or strand of molecule structure. also called point mutation single-strand break
result is cleaved or broken chromosome, each new portion has unequal amount of genetic info. . Culminates in death or impaired function of daughter cell double-strand break in same rung of DNA
loss or change of a base in the DNA chain mutation
chemical unions created between atoms by the single sharing of one or more pairs of electrons. initiated by high-energy radiation Covalent Cross-Links
result when irradiation occurs early in interphase, before DNA synthesis takes place. Break caused by rad in single strand of chromatin, break is replicated when chromatin lays down identical strand adjacent to itself chromosome abberations
result when irradiation occurs after interphase. Only one chromatid of a pair might undergo a radiation-induces break, only one daughter cell affected chromatid abberations
structural changes in biologic tissue caused by ionizing radiation single or double strand break in one or more chromosome or chromatids. more than one break in same chromosome or chromatid. chromosome stickiness, or clumping together
Consequences to the Cell from structural Changes in Biologic Tissue resolution deletion broken-end rearrangement broken-end rearrangement without visible damage to chromatids
breaks rejoin in original configuration. No damage occurs resolution
part of chromosome or chromatid is lost at next cell division, creating aberration known as acentric fragment deletion
grossly misshapen chromosome produced. Ring chromatids, dicentric chromosomes, anaphase bridges examples broken-end rearrangement
genetic material rearranged even though chromatid appears normal. Translocations example. broken-end rearrangement without visible damage to chromatids
DNA is irreplaceable master, or key, molecule that serves as vital target. Damage and death may occur to redundant macromolecules without cell showing signs of damage afterwards target theory
Cellular effects of ionizing radiation instant death; reproductive death; apoptosis, or programmed cell death (interphase death); mitotic, or genetic, death; mitotic delay; interference with function; chromosome breakage
Occurs from X-ray or Gamma dose of 1000Gy in a period of seconds or few minutes instant death
1-10Gy doses, cell does not die, but loses its ability to procreate. Continues to function, but reproductive death prevents damage from being passed on reproductive death
cells die without attempting division during interphase. Formerly called interphase death. Occurs spontaneously in both normal tissue and tumors. Example of process is when tadpoles lose their tails Apoptosis (programmed cell death)
governs the dose required to cause apoptosis radiosensitivity of the cell
Radiation may retard or permanently inhibit mitotic process. Cell death follows permanent inhibition. death occurs when a cell dies after one or more divisions mitotic death
Can be caused by as little as .01Gy if exposed just before division – cell fails to start dividing on time mitotic delay
constructed data obtained by a series of experiments. Tests cell’s abilities to survive doses of radiation Cell Survival Curve
highly radiosensitive cells Basal cells of skin, Blood cells - lymphocytes & erythroblasts, Intestinal crypt cells, Spermatagonia
intermediately radiosensitive cells endothelial cells, osteoblasts, spermatids, fibroblasts
low radiosentive cells muscle, nerve, and brain cells
highly radiosensitive tissues lymphoid tissue, bone marrow, gonads
intermediately radiosensitive tissue skin, GI tract, cornea, growing bone, kidney, liver, thyroid
low radiosensitive tissue muscle, brain and spinal tissue
influence of oxygen on indirect damage More oxygen present increases production of free radicals which in turn increases indirect damage potential of radiation
radiosensitivity was a function of the metabolic state of the cell receiving the exposure Law of Bergonié and Tribondeau
radiosensitivity of cells is directly proportional to their reproductive activity and inversely proportional to their degree of differentiation Law of Bergonié and Tribondeau
most pronounced radiation effects occur in cells having least maturity and specialization, or differentiation; the greatest reproductive activity, and longest mitotic phases Law of Bergonié and Tribondeau
Whole body dose of __ within a few days produces measurable hematologic depression .25Gy
radiation primarily effects __ of blood-forming system stem cells
Death typically caused by in high doses of radiation to hematopoietic system infection that cannot be overcome by the immune system because of destruction of myeloblasts and internal hemorrhage resulting from destruction of megakaryoblasts
LD 50/60 for humans without medical intervention 3-4Gy
LD 50/60 for humans with medical intervention 5-6Gy
the most radiosensitive blood cells in human body Lymphocytes manufactured in bone marrow
Normal WBC count for adult 5000 – 10,000/mm3 of blood.
5Gy can cause reduction in number of neutrophils - body has hard time fighting infection .5Gy
scavenger type of wbc that fight bacteria Granulocytes
Effects of Ionizing radiation on Granulocytes Cells respond to radiation by suddenly increasing in number
Normal platelet count in human adult 150,000 – 350,000/mm3 of blood
Dose of __lessens number of platelets .5Gy
why occupational doses not measured by blood tests Blood test unable to indicate exposure less than 10cGy
Window of sensitivity __after gestation 8-15 weeks
Lower level risk remains until __, at which risk is not found to be significantly different from that of young adults week 25
During maximum sensitivity, .1Sv fetal EqD is associated with as much as 4% risk of mental retardation.
.1Gy and under fx on reproductive system Depress sperm population, Menstrual irregularities
.1Gy and higher fx on reproductive system Genetic mutations in sperm, Postpone conception for 30 days or more for females
2Gy fx on reproductive system Temp. sterility up to 1 yr
5-6Gy fx on reproductive system Permanent sterility
dose that may be tolerated by females in fractionated doses 20Gy fractionated
Created by: jen.studer