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Sherer Ch6
| Question | Answer |
|---|---|
| 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
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