Thyroid cancer after radiotherapy for skin hemangioma in infancy.

A Swedish cohort of 14,351 infants exposed to ionizing radiation for skin hemangioma was analyzed with respect to thyroid cancer risk. The subjects were irradiated during the period 1920-1959 and radiotherapy was given with beta particles, gamma rays and/or X rays. The mean absorbed dose to the thyroid was 0.26 Gy (range < 0.01-28.5 Gy). The cohort was matched with the Swedish Cancer Register for the period 1958-1986. Seventeen thyroid cancers were registered (standardized incidence ratio = 2.28; 95% confidence interval 1.33-3.65), and the mean thyroid absorbed dose in those subjects was 1.07 Gy (range < 0.01-4.34 Gy). The effect of different variables on the incidence of thyroid cancer was evaluated with Poisson regression. The excess in thyroid cancer began 19 years after radiotherapy and persisted at least 40 years after irradiation. A statistically significant dose-response relationship was found. The excess relative risk per gray was 4.92 (95% CI 1.26-10.2) and the excess absolute risk was 0.90 x 10(-4) per person-year gray. No significant difference in excess relative or absolute risk could be seen between the sexes.