LEUKEMIA MORTALITY AFTER X-RAY TREATMENT FOR ANKYLOSING-SPONDYLITIS

Leukemia mortality has been studied in 14,767 adult ankylosing spondyl itis patients diagnosed between 1935 and 1957 in the United Kingdom, o f whom 13,914 patients received X-ray treatment. By 1 January 1992, th ere were 60 leukemia deaths among the irradiated patients, almost treb le that expected from national rates, Leukemia mortality was not incre ased among unirradiated patients, Among those irradiated, the ratio of observed to expected deaths for leukemia other than chronic lymphocyt ic leukemia was greatest in the period 1-5 years after the first treat ment (ratio = 11.01, 95% confidence interval 5.26-20.98) and decreased to 1.87 (95% confidence interval 0.94-3.36) in the 25+ year period, T here was no significant variation in this ratio with sex or age at fir st treatment, The ratio for chronic lymphocytic leukemia was slightly but not significantly raised (ratio = 1.44, 95% confidence interval 0. 62-2.79). Most irradiated patients received all their exposure within a year. Based on a 1 in 15 random sample, the mean total marrow dose w as 4.38 Gy, Doses were nonuniform, with heaviest doses to the lower sp ine. The risk for nonchronic lymphocytic leukemia was adequately descr ibed by a linear-exponential model that allowed for cell sterilization in heavily exposed parts of the marrow and time since exposure, Ten y ears after first exposure, the linear component of excess relative ris k was 12.37 per Gy (95% confidence interval 2.25-52.07), and it was es timated that cell sterilization reduced the excess relative risk by 47 % at 1 Gy (95% confidence interval 17%-79%). The average predicted rel ative risk in the period 1-25 years after exposure to a uniform dose o f 1 Gy was 7.00. (C) 1995 by Radiation Research Society