Revision 1
March 19, 1998
by Radiation, Science, and Health, Inc.,
Edited by J. Muckerheide

1.2.3
Medical

1.2.3.2
Medical Patients

"The widely accepted concept that the alpha-emitting radionuclides radon (Rn-222, Rn-220) induces lung tumors in humans has been based on the excess of lung cancers observed in underground miners extract-ing uranium and other substances. However, this poses the important question of whether radon is the only carcinogenic factor because such miners were also heavily exposed to mine dusts including silicates, diesel exhaust, etc. in their working environment. Patients to whom Thorotrast was administered continuously exhale radon (Rn-220) derived from Th-232 deposits in the body and therefore provide a good model for lung carcinogenesis by radon without concomitant dust exposure. To clarify the role of radon in lung carcinogenesis, we measured both body Th-232 burden and exhaled Rn-220 in Thorotrast patients, and also analyzed lung tumors arising in Thorotrast patients histopathologically (Ishikawa et al 1992, Mori 1995)."

"Results:"

"The radioactivity of Rn-220 in the breath of a standard Thorotrast patient (25 cGy/yr to the liver) is 28,000 Bq/m3 (Table I)."

"The O/E ratio of death due to lung cancer was only 1.8, which means no statistically significant increase."

TABLE I - COMPARISONS OF RADIOACTIVITIES OF ALPHA-EMITTERS IN LUNG OR IN THE ATMOSPHERE AMONG VARIOUS POPULATIONS

(1) Average activity concentration in the breath of 220-Rn for the standard autopsy case (see text).
(2) Radioactivity concentrations in a Yugoslav mine (from 90 pCi/l (in the tunnels) to 800 pCi/l (in poorly-ventilated stopes)) (UNSCEAR 1977).
(3) Activity concentrations in an Austrian hot spring (from 10 pCi/l (in room air) to 3,000 pCi/l (in a thermal gallery)) (UNSCEAR 1977).
(4) Average indoor activity for this population (Mifune et al 1992).