Bush__The_Essential_Physics_for_Medical_Imaging - Biomedical ...

TABLE 25-7. SUMMARY OF MAJOR EPIDEMIOLOGIC INVESTIGATIONS THAT FORM THE BASIS OF CURRENT CANCER DOSE-RESPONSE ESTIMATES IN HUMAN POPULATIONsaThe analysis of the atom-bomb survivors is thesingle most important cohort which influencecurrent radiation-induced cancer risk estimates.The population is large and there is a wide rangeof doses from which it is possible to makedeterminations of the dose-response and theeffects of modifying factors such as age on theinduction of cancer. Data at high doses are limited,thus the analysis only included individuals in whichthe doses to internal organs were less than 4 Gy(400 rad). The survivors were not representative ofa normal Japanese population insofar as many ofthe adult males were away on military servicewhile those remaining presumably had somephysical condition preventing them from activeservice. In addition, children and the elderlyperished shortly after the detonation in greaternumbers than did young adults, suggesting thepossibility that the survivors may represent ahardier subset of the population.Population and exposureStrengths and limitationsAtomic-bomb survivors: A mortality study ofapproximately 120,000 residents of Hiroshima andNagasaki (1950) among which 93,000 wereexposed at the time of the bombing. This groupcontinues to be followed. The mortalityassessment through 1987 has been completed.New dose estimates were made which determinedthat neutrons were not, as previously thought, asignificant component of the dose for either ofthe two cities. Mean organ doses have beencalculated for twelve organs. Approximately20,000 received doses of 10-50 mGy (1-5 rad)while -1,100 received doses in excess of2 Gy (200 rad).A total of 483 excess cancers are thought to havebeen induced by radiation exposure resulting in anexcess cancer mortality of 205. The naturalincidence for this population would havepredicted 2,670 cancers. The number of expected,observed, and excess cancers by organ system isshown below. These data apply to the 41,000persons who received 0.01 Sv (1 rem) or more. Themean dose was 0.23 Sv (23 rem). No statisticallysignificant radiation-related increases wereobserved for uterus, cervix, pancreas, rectum,multiple myeloma, non-Hodgkin's lymphoma, orchronic lymphocytic leukemia.Incidence dataBreast 200 295Lung 365 456Stomach 1222 1307Leukemia 67 141Thyroid 94 132Colon 194 223Skin 76 98Bladder 98 115Liver 95 109Esophagus 79 84Brain and central 67 71nervous systemBone and connective 12 16tissueNon-Hodgkin's 72 76LymphomaMultiple myeloma 29 30TOTAL 2,670 3,153