Relative biological effectiveness of radon: An in vitro study using chromosome aberrations as a biomarker

Purpose : The need to determine a reliable relative biological effectiveness (RBE) value for alpha exposures has become important as reports remain controversial. Although a radiation-weighting factor of 20 has been designated for alpha particles, uncertainty exists on realistic value of the RBE of alpha radiation. The aim of this study was to estimate RBE values for radon using chromosome aberrations as the endpoint in respect to various dose rates of gamma radiation. Materials and methods : Human blood samples were exposed ex vivo to different doses of radon ranging from 0.0011-0.008 Gy. Blood samples were also exposed to gamma radiation with dose rates of 1, 0.1, 0.01 and 0.001 Gy/min. Chromosome aberrations in giemsa-stained first division metaphase preparations were scored. Results : Dose response curves for dicentric chromosomal aberration yields were generated for both radon and gamma rays. Radon dose rates were compared with gamma dose rates to deduce RBE values. The values obtained were 16, 25, 29 and 38 for reference gamma dose-rates of 1, 0.1, 0.01 and 0.001 Gy/min, respectively. Conclusions : The study indicates that an RBE value of radon can range between 16 and 38, if one were to consider chromosome aberrations as an effective biomarker of risk due to ionizing radiation.