Dosimetric Comparison of Exposure Pathways to Human Organs and Tissues in Radon Therapy

Abstract

Three therapeutic applications are presently prescribed in the radon spas in Gastein, Austria: exposure to radon in a thermal bath, exposure to radon vapor in an exposure chamber (vapor bath), and exposure to radon in the thermal gallery, a former mine. The radiological exposure pathways to human organs and tissues in these therapeutic radon applications are inhalation of radon and radon progeny via the lungs, radon transfer from water or air through the skin, and radon-progeny deposition on the skin in water or air. The objectives of the present study were to calculate radon and radon-progeny doses for selected organs and tissues for the different exposure pathways and therapeutic applications. Doses incurred in red bone marrow, liver, kidneys, and Langerhans cells in the skin may be correlated with potential therapeutic benefits, while doses to the lungs and the basal cells of the skin indicate potential carcinogenic effects. The highest organ doses among the three therapeutic applications were produced in the thermal gallery by radon progeny via inhalation, with lung doses of 5.0 mSv, and attachment to the skin, with skin doses of 4.4 mSv, while the radon contribution was less significant. For comparison, the primary exposure pathways in the thermal bath are the radon uptake through the skin, with lung doses of 334 μSv, and the radon-progeny attachment to the skin, with skin doses of 216 μSv, while the inhalation route can safely be neglected.

Radon Solubility and Diffusion in the Skin Surface Layer

“…On the other hand, the latter appears to be an extreme situation whose impact should be debated. That is, it will be examined how D SC is changed if not P SC/water = P sebum/water = 33.3 (Table 1) but P SC/water = P skin/water = P skin/blood P blood/air P air/water = 0.4 × 0.43 × 5.2 = 0.89 (i.e., another extreme assumption) is assigned to Equation (5). If P SC/water was considered to be 33.3 or 0.89 (in the case of all male subjects), the examination of Nagy's human data [16] revealed the following D SC : for P SC/water = 33.3, the same as the case for L SC = 10 µm shown in the above paragraph; for P SC/water = 0.89, GM 2.4 × 10 −12 m 2 s −1 (GSD = 3.4), 5th percentile 3.2 × 10 −13 m 2 s −1 , and 95th percentile 1.8 × 10 −11 m 2 s −1 .…”

“…Although the mobility of radon decay products should be explored further in the future, the current study provides important information on the position of radon as a radiation source for special dose evaluation when specific target cell layers are assumed for the skin. Basal cells positioned at the bottom layer of the epidermis and Langerhans cells existing uniformly in the epidermis have been considered as target cells from the viewpoint of radiation risk and radon spa therapy, respectively [5,6]. It would be fascinating to learn more about how radon is distributed within the skin (in particular, the viable skin), which could help with dose evaluation.…”

“…Making model structures and their related parameterization for such pathways has recently been enhanced to better mimic empirical data from human research on their activity concentrations in organs and tissues as well as on the skin surface during or after the exposure. Using convenient assumptions as well as parameters such as a skin permeability coefficient defined in [3,4], the models can work for purposes dedicated to generic dose assessments from the viewpoint of radiation protection or therapeutic application [5,6]. There is still a lot of work to be done in terms of understanding and describing the behavior of radon and its progeny at the skin.…”