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29 Cards in this Set
- Front
- Back
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radiation |
energy transmitted in particles or waves can be ionizing or non |
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radiation biology |
initial interaction between ionizing radiation and matter occurs at ion level modification of biologic molecules: secs to hours alterations in cells and organisms: hours to decades if enough cells are killed: permanent injury or death if cells are modified: cancer, genetic disorder |
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biological effects |
deterministic effects: severity is proportional to dose, based on threshold curve skin erythema, cataract formation stochastic effects: probability of occurrence increases with dose all or none, and NO THRESHOLD mutations and cancer |
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radiation chemistry |
direct ionization: energy of photon or secondary electron ionizes biological macromolecules, creates free radical 1/3 of biological effects result from direct ionization indirect ionization: water molecules absorb the photon causing radiolysis that in turn interacts with biological macromolecules OH and HO2 are oxidizing agents that can alter biologic molecules and cause cell destruction |
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indirect effects |
molecules interact with free radicals, resulting in permanent damage: 2/3 of radiation induced biologic damage free radicals: electrically neutral atoms or molecules that have an unpaired electron in the outer orbits |
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changes in biological molecules |
nucleic acids: change or loss of a base disruption of H bonds breakage of DNA strands cross-linking of DNA strands proteins: change secondary and tertiary structures |
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radiation effects at cellular levels |
nucleus is more sensitive than cytoplasm G2 and M phases are most sensitive reduction in size mitotic delay cell death |
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chromosome aberrations |
observed in irradiated cells at time of mitosis, when DNA condenses to form chromosomes a piece falls off and gets: translocated >> non-lethal deleted >> non-lethal creates dicentric formation >> lethal forms ring >> lethal FREQUENCY of aberrations is GENERALLY proportional to the radiation DOSE received (stochastic) |
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survival curve |
response of cells to irradiation: curve shoulder - accumulation of sublethal damage/repair dose D0 - slope of straight portion of the curve D0 - measures amount of radiation required to reduce number of colony forming cells to 37% |
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cell recovery |
enzymatic repair of SINGLE-STRAND breaks of DNA: if dose fractioned, more total dose required to cause cell death if DOUBLE-STRAND breaks of DNA, no recovery, lethal to cell |
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law of bergonie and tribondeau |
undifferentiated cells are radiosensitive differentiated cells are less radiosensitive or more radioresistant lymphocytes and oocytes are exceptional |
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radiosensitive tissues |
high: lymphoid hemopoietic gonadal epithelium intestinal epithelium low: muscle and neural erythrocytes and epithelial cells |
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radiosensitive organs |
high: lymphoid tissue bone marrow testes ovaries intestines mucous membranes low: optic lens muscle |
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factors modifying radiation effects |
dose dose rate oxygen linear energy transfer (LET) |
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linear energy transfer (LET) |
energy transferred per unit length of the track unit of LET is keV/um (kiloelectron volt per micrometer of unit density material) radiation with LET of 100 is most efficient in producing biologic damage dental beam - LET ranges from 0.7-1.7 alpha and beta radiations have high LET gamme and x-rays have low LET |
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dose and dose rate |
higher dose and higher dose rate, greater damage splitting dose into small fractions allows for repair |
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oxygen |
increased oxygen means greater damage this is due to increased amounts of H2O2 and HO2 free radicals |
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area of exposure |
the larger the area, the greater the damage |
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species |
different species have different radiosensitivities LD50 is dose required to kill 50% of population |
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chemical factors |
radiosensitizer: O2 and halogenated pyrimidines radioprotectives: cysteine and glutathione |
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hematopoietic syndrome |
2-7 Gy latent period: few days to few weeks bone marrow transplant can save patient |
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GI syndrome |
7-15 Gy onset within a few hours death within 2 weeks |
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CNS syndrome |
more than 50 Gy death within 2 days |
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carcinogenic effects |
skin cancer leukemia osteosarcoma thyroid cancer |
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genetic effects |
gene mutations or chromosome mutations manifest years later transmitted to descendants no threshold dose |
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radiation effects on oral tissues |
therapeutic dose: 50Gy or 5000 rads (10Gy/week) developmental abnormalities: high radiation dose may inhibit tooth and jaw growth skin and mucosa: erythema and mucositis a few days after radiation taste buds: partial or complete loss of taste salivary glands: change saliva's volume, viscosity, pH, inorganic and organic constituents xerostomia stimulate salivary glands with pilocarpine of artificial saliva caries: rampant cervical region due to xerostomia |
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osteoradionecrosis |
osteoblasts are sensitive to radiation bone can absorb more radiation mandible is more often involved by of limited blood supply |
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late somatic effects |
carcinogenesis thyroid cancer, from irradiation of: scalp for ring worms thymus gland survivors of atomic accidents limited growth and development mental retardation cataracts |
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gene mutations - doubling dose |
amount of radiation the population requires to produce, in the next generation, as many additional mutations as arise spontaneously |
