Bone cancers induced by 224 Ra (Th X) in children and adults.

Abstract

The average skeletal dose in rads was calculated for 217 juveniles and 708 adults injected with 224Ra (mainly during the years 1946–1951) for the treatment of tuberculosis, ankylosing spondylitis and other diseases. We determined experimentally that for each 1000 esE stated by the supplier, about 140 μCi 224Ra was injected. For each injected μCi 224Ra, the average dose in rads to the marrow-free skeleton was calculated to be: 0.6 for children aged 1–15 yr; 0.4 for adolescents aged 16–20 yr; and 0.2 for adults, with each of these values multiplied by the ratio 70 kg/body mass to adjust for body size. The dose from long-lived contaminants appears small compared to that from 224Ra. The total incidence of induced bone sarcomas increased with dose in approximately linear fashion at 1.4% per 100 rads average skeletal dose for the combined juveniles and 0.7% per 100 rads average skeletal dose for the adults. Among the 49 patients developing bone sarcomas as of April 1969, the lowest average skeletal dose was 90 rads, and this patient was an adult. This is much less than the lowest average skeletal dose at death (1200 rads) among the American dial painters who developed bone sarcomas following ingestion of long-lived 1600-yr 226Ra. This difference seems mainly due to the short 3.62 day half life of 224Ra which causes a large fraction of the skeletal 224Ra to decay while still on bone surfaces. The mean local dose to the cells 0–10 μ from the mineralized bone surfaces is perhaps 9 times the average skeletal dose for 224Ra (assuming half of the skeletal 224Ra decays on bone surfaces and half within the mineral volume), whereas for long-lived 226Ra randomly distributed throughout the mineral volume, the mean local dose 0–10 μ from the bone surface is about 0.63 times the average skeletal dose. The effectiveness of 224Ra was similar in males and females, and was similar in patients with and without bone disease at the time of 224Ra injection. Bone sarcomas occurred in 1% of the 402 German spondylitis patients whose skeletal doses from 224Ra averaged 140 rads. This incidence equals the 1% combined incidence of excess leukemia plus excess cancers in the British spondylitis patients whose X-ray doses to the spinal marrow averaged about 1000 rads. None of the 21 soft-tissue tumors seems positively related to irradiation (at this time) but correlations may emerge as additional tumors develop. No carcinomas of the head cavities have yet appeared. Two leukemias are recorded, but it is uncertain whether or not these were radiation-induced.