In-vivo dose determination in a human after radon exposure: proof of principle

[Biological mechanisms of radon therapy: experimental and clinical aspects. (Literature review)]

Application of radon baths with natural and artificial radon-containing waters is one of the common methods of non-drug therapy in the treatment of inflammatory and degenerative diseases of different origin in sanatoriums and wellness centers in many Russian and foreign health resorts. Radon therapy is most often used as an additional method in the structure of multimodal health resort treatment in diseases of the musculoskeletal system. The article presents an analysis of Russian and foreign experience in the application of radon-containing mineral waters and evidence-based approaches in the study of cellular and molecular mechanisms of radon action. Experimental data on the quantification of intake and excretion of radon and its daughter products after the application of mineral water with different radon concentrations are provided on the biokinetic models. According to the literature, radon procedures have analgesic and anti-inflammatory effects, affecting osteoclastogenesis and bone resorption. The authors associate this therapeutic effect of radon with contribution of the immune system and change in the Th17/Treg-cell ratio after receiving balneotherapy. It has been noted that a deeper study of the development of therapeutic effects from radon procedures application within the framework of high-quality placebo-controlled biomedical studies in experiment and clinical setting is needed in order to increase the evidence level of therapy using radon as well as for assessment of potential side effects and risks of carcinogenesis.

Osteo-immunological impact of radon spa treatment: due to radon or spa alone? Results from the prospective, thermal bath placebo-controlled RAD-ON02 trial

Musculoskeletal disorders (MSDs) are associated with pain and lead to reduced mobility and quality of life for patients. Radon therapy is used as alternative or complementary to pharmaceutical treatments. According to previous reports, radon spa leads to analgesic and anti-inflammatory effects, but the cellular and molecular mechanisms are widely unknown. A previous study (RAD-ON01) revealed, that bone erosion markers like collagen fragments (C-terminal telopeptide, CTX) are reduced after radon spa treatment in serum of patients with degenerative MSDs. Within the scope of the prospective, placebo-controlled RAD-ON02 trial presented here, we analyzed the influence of radon and thermal spa treatment on osteoclastogenesis. From patient blood, we isolate monocytes, seeded them on bone slices and differentiated them in the presence of growth factors into mature osteoclasts (mOCs). Subsequent analysis showed a smaller fraction of mOCs after both treatments, which was even smaller after radon spa treatment. A significantly reduced resorbed area on bone slices reflects this result. Only after radon spa treatment, we detected in the serum of patients a significant decrease of receptor activator of NF-κB ligand (RANKL), which indicates reduced differentiation of OCs. However, other markers for bone resorption (CTX) and bone formation (OPG, OCN) were not altered after both treatments. Adipokines, such as visfatin and leptin that play a role in some MSD-types by affecting osteoclastogenesis, were not changed after both treatments. Further, also immune cells have an influence on osteoclastogenesis, by inhibiting and promoting terminal differentiation and activation of OCs, respectively. After radon treatment, the fraction of Treg cells was significantly increased, whereas Th17 cells were not altered. Overall, we observed that both treatments had an influence on osteoclastogenesis and bone resorption. Moreover, radon spa treatment affected the Treg cell population as well as the Th17/Treg ratio were affected, pointing toward a contribution of the immune system after radon spa. These data obtained from patients enrolled in the RAD-ON02 trial indicate that radon is not alone responsible for the effects on bone metabolism, even though they are more pronounced after radon compared to thermal spa treatment.

Radon progeny measurements in a ventilated filter system to study respiratory-supported exposure

Radon (222Rn) and its progeny are responsible for half of the annual dose from natural radiation and the most frequent cause for lung cancer induction after smoking. During inhalation, progeny nuclides accumulate in the respiratory tract while most of the radon gas is exhaled. The decay of progeny nuclides in the lung together with the high radiosensitivity of this tissue lead to equivalent doses implying a significant cancer risk. Here, we use gamma spectroscopy to measure the attachment of radon progeny on an air-ventilated filter system within a radon enriched atmosphere, mimicking the respiratory tract. A mathematical model was developed to describe the measured time-dependent activities of radon progeny on the filter system. We verified a linear relation between the ambient radon activity concentration during exposure and the amount of decay products on the filter system. The measured activities on the filters and its mathematical description are in good agreement. The developed experimental set-up can thus serve to further investigate the deposition of radon progeny in the respiratory tract under varying conditions for determination of dose conversion factors in radiation protection, which we demonstrate by deriving dose estimations in mouse lung.

Experimental Setups for In Vitro Studies on Radon Exposure in Mammalian Cells-A Critical Overview

Naturally occurring radon and its short lived progeny are the second leading cause of lung cancer after smoking, and the main risk factor for non-smokers. The radon progeny, mainly Polonium-218 (²¹⁸Po) and Polonium-214 (²¹⁴Po), are responsible for the highest dose deposition in the bronchial epithelium via alpha-decay. These alpha-particles release a large amount of energy over a short penetration range, which results in severe and complex DNA damage. In order to unravel the underlying biological mechanisms which are triggered by this complex DNA damage and eventually give rise to carcinogenesis, in vitro radiobiology experiments on mammalian cells have been performed using radon exposure setups, or radon analogues, which mimic alpha-particle exposure. This review provides an overview of the different experimental setups, which have been developed and used over the past decades for in vitro radon experiments. In order to guarantee reliable results, the design and dosimetry of these setups require careful consideration, which will be emphasized in this work. Results of these in vitro experiments, particularly on bronchial epithelial cells, can provide valuable information on biomarkers, which can assist to identify exposures, as well as to study the effects of localized high dose depositions and the heterogeneous dose distribution of radon.

Radon Solubility in Different Tissues after Short Term Exposure

Radon, a naturally occurring radioactive noble gas, contributes significantly to lung cancer when incorporated from our natural environment. However, despite having unknown underlying mechanisms, radon is also used for therapeutic purposes to treat inflammatory diseases such as rheumatoid arthritis. Data on the distribution and accumulation of radon in different tissues represent an important factor in dose determination for risk estimation, the explanation of potential therapeutic effects and the calculation of doses to different tissues using biokinetic dosimetry models. In this paper, radon's solubility in bones, muscle tissue, adipose tissue, bone marrow, blood, a dissolved gelatin and oleic acid were determined. In analogy to current radon use in therapies, samples were exposed to radon gas for 1 h using two exposure protocols combined with established γ-spectroscopic measurements. Solubility data varied over two orders of magnitude, with the lowest values from the dissolved gelatin and muscle tissue; radon's solubility in flat bones, blood and adipose tissue was one order of magnitude higher. The highest values for radon solubility were measured in bone marrow and oleic acid. The data for long bones as well as bone marrow varied significantly. The radon solubility in the blood suggested a radon distribution within the body that occurred via blood flow, reaching organs and tissues that were not in direct contact with radon gas during therapy. Tissues with similar compositions were expected to reveal similar radon solubilities; however, yellow bone marrow and adipose tissue showed differences in solubility even though their chemical composition is nearly the same-indicating that interactions on the microscopic scale between radon and the solvent might be important. We found high solubility in bone marrow-where sensitive hematopoietic cells are located-and in adipose tissue, where the biological impact needs to be further elucidated.

The Influence of Adopting New Reference Breathing Parameters on ICRP66 Model on the Regional Deposition of the Inhaled Attached Radon-222 Daughters Within the Human Airways

The radiation dose from internal radiation exposure is difficult to measure directly and hence different lung models were developed. The dose on the lung is the result of the regional deposition of aerosols carrying radon daughters in the respiratory tract. Deposition of aerosols can be take place during inhalation and exhalation in the 5 regions of the respiratory tract due to variation of aerosol sizes and other biological factors such as breathing rate. In this paper, a modified breathing rate is instead applied on the assumptions developed by the ICRP66 model to analyze the regional deposition of radioactive aerosols and a comparison has been made with the result of ICRP66 model deposition. According to the result, as the diameter of aerosols increases from 1 to 10 μm, the percentage deposition fraction in extrathoracic regions, in ET1 region increases from 6.53% to 48.43% and in ET2 region increases from 7.3% to 50.33%. The aerodynamic deposition of the attached fraction of radon aerosols along the bronchial regions (bronchi (BB), and bronchiolar (bb) region) is found small and almost constant. For 1 μm diameter aerosols, the percentage deposition is found 0.82%, for 5 μm diameter aerosols, the deposition is predicted 2.56% and at 10 μm the deposition is predicted about 1.93% in bronchi (BB) region. In the bronchiolar region (bb) for 1 μm aerosols, the deposition predicted is 1.5% and at 10 μm about 0.88% is predicted. The deposition of small size attached fraction of radon aerosols is found maximum in the alveolar region as compared to other regions of the respiratory tract and the deposition becomes almost negligible for large size aerosols in this region.

Effects of spatial variation in dose delivery: what can we learn from radon-related lung cancer studies?

Exposure to radon progeny results in heterogeneous dose distributions in many different spatial scales. The aim of this review is to provide an overview on the state of the art in epidemiology, clinical observations, cell biology, dosimetry, and modelling related to radon exposure and its association with lung cancer, along with priorities for future research. Particular attention is paid on the effects of spatial variation in dose delivery within the organs, a factor not considered in radiation protection. It is concluded that a multidisciplinary approach is required to improve risk assessment and mechanistic understanding of carcinogenesis related to radon exposure. To achieve these goals, important steps would be to clarify whether radon can cause other diseases than lung cancer, and to investigate radon-related health risks in children or persons at young ages. Also, a better understanding of the combined effects of radon and smoking is needed, which can be achieved by integrating epidemiological, clinical, pathological, and molecular oncology data to obtain a radon-associated signature. While in vitro models derived from primary human bronchial epithelial cells can help to identify new and corroborate existing biomarkers, they also allow to study the effects of heterogeneous dose distributions including the effects of locally high doses. These novel approaches can provide valuable input and validation data for mathematical models for risk assessment. These models can be applied to quantitatively translate the knowledge obtained from radon exposure to other exposures resulting in heterogeneous dose distributions within an organ to support radiation protection in general.