The proportion of thyroid cancers in the Japanese atomic bomb survivors associated with natural background radiation.
Generalised absolute and relative risk models (with adjustment to the excess absolute risk for time since exposure and age at exposure, and with adjustment to the excess relative risk for age at exposure) are fitted to the Japanese atomic bomb survivor thyroid cancer incidence data followed up over the period 1958-87, taking account of natural background radiation. Thyroid cancers associated with natural background radiation and atomic bomb radiation are overwhelmingly accounted for by exposure at young ages. Over 50% of the excess cases associated with either the atomic bomb radiation or natural background radiation are linked to exposures under the age of 20, irrespective of the assumed risk model or natural background dose rate. The excess risk is overwhelmingly concentrated among females, again irrespective of the assumed model or natural background dose rate. Depending on the assumed natural background dose rate (in the range 0.5-2.0 mSv/year) between 17.3 and 32.0% of the thyroid cancer in this cohort may be associated with natural background radiation if an absolute risk model applies; between 4.2 and 17.1% of the thyroid cancers may be associated with natural background radiation if the relative risk model applies. The proportion of the thyroid tumours attributed to the atomic bomb radiation is between 21.1 and 22.0% for the absolute risk model, and is between 18.7 and 19.1% for the relative risk model, in both cases irrespective of the assumed background radiation dose. In particular, these proportions are not very different from the proportions calculated when fitting models that do not take account of natural background radiation, namely 22.0% for the absolute risk model and 18.6% for the relative risk model. The proportion of thyroid cancers accounted for by natural background radiation progressively increases with attained age, from 0.3% of cancers among those under the age of 15 to 30.5% for those over the age of 60, assuming that the absolute risk model applies. There is a similar increase in this percentage, if to a rather lower level (from 0.2 to 10.2%), assuming that the relative risk model applies.
Little
M P
MP
Department of Epidemiology and Public Health, Imperial College of Science, Technology and Medicine, London, UK. mark.little@ic.ac.uk
D000293:Adolescent; D000328:Adult; D001417:Background Radiation; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D004307:Dose-Response Relationship, Radiation; D005260:Female; D006801:Humans; D015994:Incidence; D007564:Japan / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D009381:Neoplasms, Radiation-Induced / Q000453:epidemiology*; D009689:Nuclear Warfare; D012307:Risk Factors; D013964:Thyroid Neoplasms / Q000453:epidemiology*; D013997:Time Factors