Late Effects in Ankylosing Spondylitis Patients Treated with 224 Ra

Abstract

This study is comprised of 1577 ankylosing spondylitis patients from 9 German hospitals who have been treated with multiple injections of (224)Ra. The majority of the patients, most of them treated in the years 1948-1975, received one series of 10 weekly intravenous injections of about 1 MBq of (224)Ra each. This dose leads to a mean absorbed dose due to alpha-particle radiation of 0.56 Gy to the marrow-free skeleton of a 70- kg man (mean bone surface dose of about 5 Gy). To provide comparative information on causes of death and on health effects possibly related to the basic disease itself, a control group of 1462 ankylosing spondylitis patients with roughly the same age distribution has been established. By the end of 1998, 649 patients in the exposed group and 762 control patients had died. Among other observations, it is of particular interest that 13 cases of leukemia in the exposed group have been observed. This is a highly significant excess (P < 0.001) compared to a standard population, but only a marginally significant excess in comparison to the seven cases observed in the control group. Subclassification of the leukemias shows a clear preponderance of the myeloid leukemias in the exposed group (8 cases observed compared to 1.7 cases expected, P < 0.001), whereas in the control group the observed cases are within the expected range for myeloid leukemia (3 cases observed compared to 2.2 cases expected, P = 0.3). The (224)Ra cohort of the earlier study (higher-dose group) has provided a risk coefficient that predicts about 8 excess malignant bone tumors for the irradiated cohort in this study. In actuality, 4 cases of malignant tumors in the skeleton have been observed so far. However, excess of breast cancer has not been observed in either the irradiated or the control group, which is in contrast to the findings in the earlier (224)Ra cohort of Study I.