Radiation Effects Flashcards
Gy
Joules per kg
Relative Biological Effectiveness (RBE)
ratio of the dose of 250 keV x-rays to the dose of the test radiation that produce an equivalent biological effect.
Dose Equivalent
Dose times quality factor (QF), arbitrarily assigned
Effective Dose Equivalent
Dose equivalent multiplied by a weighting function depending on the tissue that is irradiated.
Direct and Indirect Mechanisms of Cellular Damage
Particle damages the cells directly in DNA or other components, or for indirect, cytoplasm has ionization that produces free radical species
Direct cellular damage can result in:
cell death or point mutation, or fatal mutation for the next generation
Indirect cellular damage can result in:
membrane instability, DNA damage in cytoplasm, radical species
Reactive Species Formed by Ionization
Free Radicals, Hydrogen Peroxide, Superoxide, Ozone
Radiation effect during different cell cycles
Most sensitive in mitosis, least sensitive during S phase (where endonuclease is working the hardest)
Apoptosis and p53
p53 gene regulates mitosis, and can lead to cell death from radiation. Mutation in p53 will lead to cancer.
Mean lethal dose
Dose at which survival is 1/e (37%)
Deterministic effects of radiation
Threshold radiation at which no effect is seen exists. Severity of damage due to radiation.
Stochastic effects of radiation
Probability of cancer occurrence is stochastic. No threshold is reported for cancer occurrence.
Skin Dose and Effects
2 Gy: temporary erythema, 3 Gy: epilation, 10 Gy: desquamation, 18 Gy: necrosis
Hematopoietic Dose and Effects
0.1 Gy: chromosomal abnormalities in lymphocytes, 0.3 Gy: Lymphocytes lowered, 1 Gy: Granulocytes lowered, 4-6 Gy: increase in granulocyte count followed by total collapse
Acute Radiation Syndrome
Prodromal, 10 Gy: fever, apathy, diarrhea; Cerebrovascular, 100 Gy: death, seizure, coma; Hematopoietic, 3-8 Gy: PANcytopenia
LD-50/30 and LD-50/60
Dose to kill 50% of population in 30 or 60 days
Effect of Radiation on Fetus
Neurological system affected the most. Malformations and mental retardation possible in first and second trimester. Possible childhood cancer correlation if irradiated late in fetal development.
Absolute Risk
Incidence in EXPOSED group
Relative Risk
Incidence in exposed group / incidence in unexposed group
Excess Relative Risk
“Excess” risk caused by exposure, specifically Relative risk minus 1.
Attributable Risk
1-1/(Relative Risk)
Cancer Risk Models: BEIR VII Phase 2 (2006)
models of cancer risk based upon dose, age at exposure and attained age, linear-no threshold model assumed for all solid tumors; linear-quadratic for leukemia
Radioresistance
p53 can mutate to develop resistance to radiation for cancer cells. Also radiation increases hypoxic population to increase (since oxygen radicalizes to kill cancer)
