Thyroid cancer following scalp irradiation: A reanalysis accounting for uncertainty in dosimetry

In the 1940s and 1950s, over 20,000 children in Israel were treated for tin ea capitis (scalp ringworm) by irradiation to induce epilation. Follow-up s tudies showed that the radiation exposure was associated with the developme nt of malignant thyroid neoplasms. Despite this clear evidence of an effect , the magnitude of the dose-response relationship is much less clear becaus e of probable errors in individual estimates of dose to the thyroid gland. Such errors have the potential to bias dose-response estimation, a potentia l that was not widely appreciated at the time of the original analyses. We revisit this issue, describing in detail how errors in dosimetry might occu r, and we develop a new dose-response model that takes the uncertainties of the dosimetry into account. Our model for the uncertainty in dosimetry is a complex and new variant of the classical multiplicative Berkson error mod el, having components of classical multiplicative measurement error as well as missing data. Analysis of the tinea capitis data suggests that measurem ent error in the dosimetry has only a negligible effect on dose-response es timation and inference as well as on the modifying effect of age at exposur e.