Use of threshold-specific energy model for the prediction of effects of smoking and radon exposure on the risk of lung cancer

Radon and lung cancer: Current status and future prospects

Beyond tobacco smoking, radon takes its place as the second most significant contributor to lung cancer, excluding hereditary and other biologically related factors. Radon and its byproducts play a pivotal role in exposing humans to elevated levels of natural radiation. Approximately 10-20 % of lung cancer cases worldwide can be attributed to radon exposure, leading to between 3 % and 20 % of all lung cancer-related deaths. Nevertheless, a knowledge gap persists regarding the association between radon and lung cancer, impeding radon risk reduction initiatives globally. This review presents a comprehensive overview of the current state of research in epidemiology, cell biology, dosimetry, and risk modeling concerning radon exposure and its relevance to lung cancer. It also delves into methods for measuring radon concentrations, monitoring radon risk zones, and identifying priorities for future research.

INFLUENCE OF AIRWAY GEOMETRY ON RADON RISK ASSESSMENT IN ADULTS AND CHILDREN (MICRODOSIMETRIC APPROACH)

The aim of this work was to use the microdosimetric threshold energy model to study the effects of alpha-emitting 222Rn progeny on the probability of developing lung cancer. The results suggest that the radiation risk may increase by several times as the thickness of the surface layer decreases. The thicker the protective mucus layer and the deeper the sensitive target cells are located in the tissue, the less radiation damage the same dose produces. These findings have been applied to children of various ages. As children grow older, their lungs enlarge, the mucus layer thickens and the cells sensitive to radiation damage move deeper into the lung tissue, resulting in a reduction of radiation risk. The fraction of affected target cells is not only a function of dose but also of lung tissue depth. The results indicate that children can be several times more vulnerable to radiation than adults.

Radon and Lung Cancer: Current Trends and Future Perspectives

Simple Summary

Radon represents the main risk factor of lung cancer in non-smokers and the second one in smoking patients. In Europe, there are several radon-prone areas, but regulatory policies may vary between countries. Radon causes DNA damage and high genomic tumor instability, but its exact carcinogenesis mechanism in lung cancer remains unknown. Molecular drivers in NSCLC are more often described in non-smoker patients and a potential association between radon exposure and oncogenic-driven NSCLC has been postulated. This is an updated review on indoor radon exposure and its role in lung cancer carcinogenesis, especially focusing on its potential relation with NSCLC with driver genomic alterations. We want to contribute to rising knowledge and awareness on this still silent but preventable lung cancer risk factor.

Abstract

Lung cancer is a public health problem and the first cause of cancer death worldwide. Radon is a radioactive gas that tends to accumulate inside homes, and it is the second lung cancer risk factor after smoking, and the first one in non-smokers. In Europe, there are several radon-prone areas, and although the 2013/59 EURATOM directive is aimed to regulate indoor radon exposition, regulating measures can vary between countries. Radon emits alpha-ionizing radiation that has been linked to a wide variety of cytotoxic and genotoxic effects; however, the link between lung cancer and radon from the genomic point of view remains poorly described. Driver molecular alterations have been recently identified in non-small lung cancer (NSCLC), such as somatic mutations (EGFR, BRAF, HER2, MET) or chromosomal rearrangements (ALK, ROS1, RET, NTRK), mainly in the non-smoking population, where no risk factor has been identified yet. An association between radon exposure and oncogenic NSCLC in non-smokers has been hypothesised. This paper provides a practical, concise and updated review on the implications of indoor radon in lung cancer carcinogenesis, and especially of its potential relation with NSCLC with driver genomic alterations.

Residential Radon Exposure and Cigarette Smoking in Association with Lung Cancer: A Matched Case-Control Study in Korea

Residential radon exposure and cigarette smoking are the two most important risk factors for lung cancer. The combined effects thereof were evaluated in a multi-center matched case-control study in South Korea. A total of 1038 participants were included, comprising 519 non-small cell lung cancer cases and 519 age- and sex- matched community-based controls. Residential radon levels were measured for all participants. Multivariate logistic regression was used to calculate odds ratios (OR) for lung cancer according to radon exposure (high ≥ 100 Bq/m3 vs. low < 100 Bq/m3), smoking status, and combinations of the two after adjusting for age, sex, indoor hours, and other housing information. The median age of the participants was 64 years, and 51.3% were women. The adjusted ORs (95% confidence intervals [CIs]) for high radon and cigarette smoking were 1.56 (1.03-2.37) and 2.53 (1.60-3.99), respectively. When stratified according to combinations of radon exposure and smoking status, the adjusted ORs (95% CIs) for lung cancer in high-radon non-smokers, low-radon smokers, and high-radon smokers were 1.40 (0.81-2.43), 2.42 (1.49-3.92), and 4.27 (2.14-8.52), respectively, with reference to low-radon non-smokers. Both residential radon and cigarette smoking were associated with increased odds for lung cancer, and the difference in ORs according to radon exposure was much greater in smokers than in non-smokers.

Radon as a Tracer of Lung Changes Induced by Smoking

After smoking, exposure to radon and its progeny is the second leading cause of lung cancer. The probability of inducing lung carcinomas by inhaled radon progeny depends on the deposited radiation dose, and is significantly affected by physiological and morphometric changes induced by smoking. Due to irritation of the airways, the inhalation of cigarette smoke leads to the hyperproduction of mucus. Two concurrent processes occur: on one hand, increased production of mucus protects the target cells against radiation damage; on the other hand, in the case of long-term smokers, a chronic lung obstruction develops, causing an increase in the radiation dose to the lungs. Depending on the duration and intensity of smoking, these processes contribute to the final radiation dose with different weights. The primary objective of this study was to investigate to what extent these smoke-induced changes can modify the resulting absorbed dose of inhaled radon progeny relative to healthy nonsmokers. Since the bronchial dose depends on the degree of lung tissue damage, we have used this dose as a tool for detecting the effects of smoking on the lung epithelium. In other words, the biological effect of radon served as a tracer of changes induced by smoking.

LUNG REGENERATION IN ABSTAINING SMOKERS

Smoking modifies morphological and physiological parameters of the lungs. Due to the irritation of airways, the natural self-cleaning ability of the lungs is impaired. The mucus accumulates in the airways and various infections develop, leading to chronic bronchitis. After the cessation of smoking, the lungs of the smoker start to heal and regenerate. Cilia in the lungs start to grow again and cleanse the lungs, thus reducing the risk of infection. The regeneration of the lungs takes a long time and depends on the degree of lung damage due to smoking. The aim of this study was to reconstruct the evolution of this regeneration process in chronic smokers by using the biological effects of radon and its decay products. Thus, radon in this study served as a tracer of changes induced by smoking.

Lung cancer risk from radon exposure in dwellings in Sweden: how many cases can be prevented if radon levels are lowered?

Purpose

Residential exposure to radon is considered to be the second cause of lung cancer after smoking. The purpose of this study was to estimate the number of lung cancer cases prevented from reducing radon exposure in Swedish dwellings.

Methods

Measurements of indoor radon are available from national studies in 1990 and 2008 with 8992 and 1819 dwellings, considered representative of all Swedish dwellings. These data were used to estimate the distribution of radon in Swedish dwellings. Lung cancer risk was assumed to increase by 16 % per 100 becquerels per cubic meter (Bq/m³) indoor air radon. Estimates of future and saved cases of lung cancer were performed at both constant and changed lung cancer incidence rates over time.

Results

The arithmetic mean concentration of radon was 113 Bq/m³ in 1990 and 90 Bq/m³ in 2008. Approximately 8 % of the population lived in houses with >200 Bq/m³. The estimated current number of lung cancer cases attributable to previous indoor radon exposure was 591 per year, and the number of future cases attributable to current exposure was 473. If radon levels above 100 Bq/m³ are lowered to 100 Bq/m³, 183 cases will be prevented. If levels >200 Bq/m³ are lowered to 140 Bq/m³ (mean in the present stratum 100–200 Bq/m³), 131 cases per year will be prevented.

Conclusions

Although estimates are somewhat uncertain, 35–40 % of the radon attributed lung cancer cases can be prevented if radon levels >100 Bq/m³ are lowered to 100 Bq/m³.