Portable 220Rn detector used to assess Thorotrast exposure

Patients who are exposed by injection to the radiological contrast medium Thorotrast (232ThO2) had been considered by early researchers to be an unfortunate but important model of alpha-particle carcinogenesis in the lung as well as liver and bone marrow because they continuously exhale 220Rn, in the breath of Thorotrast patients and (as the first step to lung dosimetry) to investigate the relationship between exhaled 220Rn activity concentration (Bq L-1) and 232Th body burden. Results revealed that reliable estimation of 232Th burden by 220Rn measurement is possible because a fairly good correlation was obtained between 220Rn in the breath and the known quantity of 232Th in the body. Mean 220Rn activity concentration in the breath was 9.21 Bq L-1 g-1 of 232Th deposited in the liver and spleen. This value was very close to that published for German patients. Our data and those of other investigators indicate that apparent discrepancies in mean 220Rn activity concentration among previous studies was caused by using different 228Th:232Th activity ratios.