Age-dependent changes in oxygen tension, radiation dose and sensitivity within normal and diseased coronary arteries-Part A: dose from radon and thoron.

PURPOSE: There is mounting evidence that a significant fraction of radiation-induced mortality and years-life lost are non-cancerous in nature. This study quantifies the radon dose to the coronary artery walls, especially the intimal layer, vulnerable to the development of atherosclerosis, and associated cardiovascular disease (CVD). Two accompanying papers determine the oxygen levels (Part B) in coronary arteries and the oxygen effect for radon and other exposures (Part C).
MATERIALS AND METHODS: The alpha-radiation dose to coronary artery walls was calculated from the proportion of inhaled radon ((222)Rn), thoron ((220)Rn) and their short-lived progeny, which was not deposited in the lung and passed into blood. Age- and gender-dependent morphology and composition for the wall layers of coronary arteries were developed from published data for a normal population and also for individuals with cardiovascular disease. The alpha particle dose to the coronary artery walls was evaluated taking account the diffusion of radon from blood and the solubility of radon-gas in tissues.
RESULTS: Diseased arteries exhibited a moderate increase in the solubility of lipophylic radon (190%) in arteries with 88% luminal narrowing, as the high Rn solubility in fat was partially offset by the lower solubility in calcium deposits. The average worldwide dose rate to the diseased intimal layer from (222)Rn and its short-lived progeny was estimated to be as high as 68 muSv y(-1) per 40 Bq m(-3) in air, whereas the corresponding dose rate from (220)Rn per 0.3 Bq m(-3) in air was <or=0.1% in comparison. Gender had little influence on the dose.
CONCLUSION: The Rn dose to the coronary arteries is significant, but has a large uncertainty due to poor knowledge of Rn and its progeny concentrations in the body.