Medical Diagnostic X Rays and Thyroid Cancer

Background: Diagnostic x rays are the largest man-made source of exposure to ionizing radiation for the general population. Whether there are meaningful cancer risks as-sociated with such exposures is unclear. Most previous case-control studies have relied on recalled histories of x rays, and there is concern that completeness and accuracy of recall might differ between cancer case and control subjects. Purpose: The present study used information recorded prospectively in hospital charts to address the relationship between medical diagnostic x rays and risk of thyroid can-cer. Methods: The Swedish Cancer Registry and the Up-psala-Orebro Regional Cancer Registry were used to identify persons with papillary or follicular thyroid cancer diagnosed from January 1, 1980, through December 31, 1992, among residents of the Uppsala Health Care Region