Thyroid cancer after exposure to external radiation: A pooled analysis of seven studies
- National Institutes of Health, Bethesda, MD (United States)
- New York University Medical Center, NY (United States)
- Radiation Effects Research Foundation, Hiroshima (Japan)
- Chaim Sheba Medical Center, Tel Hashomer (Israel)
- Univ. of Illinois, Chicago, IL (United States)
The thyroid gland of children is especially vulnerable to the carcinogenic action of ionizing radiation. To provide insights into various modifying influences on risk, seven major studies with organ doses to individual subjects were evaluated. Five cohort studies (atomic bomb survivors, children treated for tinea capitis, two studies of children irradiated for enlarged tonsils, and infants irradiated for an enlarged thymus gland) and two case-control studies (patients with cervical cancer and childhood cancer) were studied. The combined studies include almost 120,000 people (approximately 58,000 exposed to a wide range of doses and 61,000 nonexposed subjects), nearly 700 thyroid cancers and 3,000,000 person years of follow-up. For persons exposed to radiation before age 15 years, linearity best described the dose response, even down to 0.10 Gy. At the highest doses (>10 Gy), associated with cancer therapy, there appeared to be a decrease or leveling of risk. For childhood exposures, the pooled excess relative risk per Gy (ERR/Gy) was 7.7 (95% CI = 2.1, 28.7) and the excess absolute risk per 10{sup 4} PY Gy (EAR/10{sup 4} PY Gy) was 4.4 (95% CI = 1.9, 10.1). The attributable risk percent (AR%) at 1 Gy was 88%. However, these summary estimates were affected strongly by age at exposure even within this limited age range. The ERR was greater (P = 0.07) for females than males, but the findings from the individual studies were not consistent. The EAR was higher among women, reflecting their higher rate of naturally occurring thyroid cancer. The distribution of ERR over time followed neither a simple multiplicative nor an additive pattern in relation to background occurrence. Only two cases were seen within 5 years of exposure. The ERR began to decline about 30 years after exposure but was still elevated at 40 years. Risk also decreased significantly with increasing age at exposure, with little risk apparent after age 20 years. 56 refs., 5 figs., 8 tabs.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 81193
- Journal Information:
- Radiation Research, Vol. 141, Issue 3; Other Information: PBD: Mar 1995
- Country of Publication:
- United States
- Language:
- English
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