Bush__The_Essential_Physics_for_Medical_Imaging - Biomedical ...

OverviewLeukemiaof Specific Cancer Risk EstimatesLeukemia is a relatively rare disease, with an incidence in the general U.S. populationof approximately 1 in 10,000. However, genetic predisposition to leukemia candramatically increase the risk. For example, an identical twin sibling of a leukemicchild has a 1 in 3 chance of developing leukemia. Although it is rare in the generalpopulation, leukemia is one of the most frequently observed radiation-induced cancers,accounting for approximately one-sixth of the mortality from radiocarcinogenesis.Leukemia may be acute or chronic, and it may take a lymphocytic ormyeloid form. With the exception of chronic lymphocytic leukemia, increases in allforms of leukemia have been detected in human populations exposed to radiationand in animals experimentally irradiated.An increase in the incidence of leukemia first appeared among the atomicbombsurvivors 2 to 3 years after the detonation and reached a peak approximately12 years after the exposure. The incidence of leukemia is influenced by age at thetime of exposure (Fig. 25-18). The younger the person is at the time of exposure,the shorter are the latency period and the period of expression. Although the incidenceof radiation-induced leukemia decreases with age at the time of exposure, sodoes the interval of increased risk. The BEIR V Committee recommended a relative-risk,nonlinear dose-response model for leukemia that predicts an excess lifetimerisk of 10 in 10,000 (i.e., 0.1 %) after an exposure to 0.1 Gy (10 fad).Thyroid cancer is also of concern after radiation exposure. It accounts for approximately6% to 12% of the mortality attributed to radiation-induced cancers. Studiesof exposed human populations indicate that females are at approximately 3 to 5C\1'E~ ::::IQ)...Ii-0Q)Co)c:Q)'t:J'u c:0~. ~~.~~. - .FIGURE 25-18. Effect of age at the time of exposure on the incidence of leukemia (all forms exceptchronic lymphocytic leukemia) among the atomic-bomb survivors. (From Ichuimaru et al. Incidence ofleukemia in atomic-bomb survivors, Hiroshima and Nagasaki 1950-1971, by radiation dose, years afterexposure, age, and type of leukemia. Technical Report RERF10-76. Hiroshima, Japan: Radiation EffectsResearch Foundation, 1976.)