Thyroid Neoplasia Following Low-Dose Radiation in Childhood

Abstract

The thyroid gland is highly sensitive to the carcinogenic effects of ionizing radiation. Previously, we reported a significant increase of thyroid cancer and adenomas among 10,834 persons in Israel who received radiotherapy to the scalp for ringworm. These findings have now been extended with further follow-up and revised dosimetry. Overall, 98 thyroid tumors were identified among the exposed and 57 among 10,834 nonexposed matched population and 5392 sibling comparison subjects. An estimated thyroid dose of 9 cGy was linked to a fourfold (95% Cl = 2.3-7.9) increase of malignant tumors and a twofold (95% Cl = 1.3-3.0) increase of benign tumors. The dose-response relationship was consistent with linearity. Age was an important modifier of risk with those exposed under 5 years being significantly more prone to develop thyroid tumors than older children. The pattern of radiation risk over time could be described on the basis of a constant multiplication of the background rate, and an absolute risk model was not compatible with the observed data. Overall, the excess relative risk per cGy for thyroid cancer development after childhood exposure is estimated as 0.3, and the absolute excess risk as 13 per 10(6) PY-cGy. For benign tumors the estimated excess relative risk was 0.1 per cGy and the absolute risk was 15 per 10(6) PY-cGy.

DIAGNOSIS IN ENDOCRINOLOGY: Quantification of cancer risk of each clinical and ultrasonographic suspicious feature of thyroid nodules: a systematic review and meta-analysis

“…Of these, 235 studies were retrieved for further investigation, and 41 studies (14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54) met the final selection criteria and were included in the analysis. All 41 studies were observational studies published in peer-reviewed journals between 1989 and 2012.…”

Risk of Thyroid Cancer in the Bryansk Oblast of the Russian Federation after the Chernobyl Power Station Accident

“…Based on human experience, the relative biological effectiveness was thought to be between zero and one-half. In reviewing the results of both animal and human studies, the NCRP suggested in its 1985 report that 131 I is one-third as effective as external radiation in producing thyroid cancer in the general population (30). It should be noted that this was intended by NCRP as a conservative value for radiation protection standards as opposed to risk estimation.…”

“…Current evidence suggests that there is a dose level above which radiation-induced carcinogenesis occurs less frequently than at lower doses (30). Animal data and limited human studies collectively suggest that at external radiation doses over 20,000 milligray (mGy) or perhaps 15,000 mGy, cell killing and sterilization reduce the risk of carcinogenesis (17,18,25,26).…”

“…The National Council on Radiation Protection (NCRP) has reviewed data from many animal studies which have suggested that 131 I is from 1/2 to less than 1/20th as effective as external radiation in inducing thyroid cancer (30). One study showed that 131 I was equally effective to external radiation in causing thyroid cancer in Long Island rats although the effect was dependent on the presence of increased TSH stimulation (39).…”

Thyroid Disruptors: How They Act and How We React

“…and an increased risk of thyroid cancer (Mushkacheva et al 2006;Pottern et al 1990;Ron et al 1995;Ron et al 1989;Schneider et al 1993;Shore et al 1993;Shore et al 2003;Yoshimoto et al 1995); however, risks from internally deposited radioactive iodine were not well studied until recently (Zablotska et al 2011;Kazakov, Demidchik, and Astakhova 1992;Shibata et al 2001;Takahashi et al 2003;Dobyns et al 1974). Well-documented examples include medical therapeutic external beam radiation and accidental exposure to c-radiation and radioiodine as a result of nuclear weapon explosions or nuclear reactor accidents (Ron et al 1995).…”