Residential radon and lung cancer risk in a high-exposure area of Gansu Province, China

Human Health Impacts of Residential Radon Exposure: Updated Systematic Review and Meta-Analysis of Case-Control Studies

This study investigated the impact of residential radon exposure on human cancers (i.e., lung cancer and childhood leukemia) through a systematic review and meta-analysis of case−control studies. A total of 9724 articles obtained from electronic databases were assessed; however, only 55 case−control studies were eligible after manually screening and eliminating unnecessary studies. The causal associations were addressed by determining the meta-analysis’s estimated size effects (i.e., ORs/RRs) of the meta-analysis. Residential radon was revealed to significantly increase the incidence of lung cancer and childhood leukemia with pooled ORs of 1.38 [1.19; 1.60] (I2 = 90%; p < 0.00001) and 1.43 [1.19; 1.72] (I2 = 0% and p = 0.51), respectively. In addition, subgroup analyses were performed to reduce the heterogeneity of the initial meta-analyses. The results provided strong evidence that inhaling radon in the indoor environments is closely associated with the development of lung cancer and childhood leukemia in patients living in Europe and areas with high radon levels (≥100 Bq/m3).

Lung cancer as adverse health effect by indoor radon exposure in China from 2000 to 2020: A systematic review and meta-analysis

Indoor radon exposure is thought to be associated with adverse health effect as lung cancer. Lung cancer incidences in China have been the highest worldwide during the past two decades. It is important to quantitively address indoor radon exposure and its health effect, especially in countries like China. In this paper, we have conducted a meta-analysis based on indoor radon and its health effect studies from a systematic review between 2000 and 2020. A total of 8 studies were included for lung cancer. We found that the relative risk (RR) was 1.01 (95% CI: 1.01-1.02) per 10 Bq/m³ increase of indoor radon for lung cancer in China. The subgroup analysis found no significant difference between the conclusions from the studies from China and other regions. The health effect of indoor radon exposure is relatively consistent for the low-exposure and high-exposure groups in the subgroup analysis. With a better understanding of exposure level of indoor radon, the outcomes and conclusions of this study will provide supports for next phase of researches on estimation of environmental burden of disease by indoor radon exposures in countries like China.

The First Attempt to Reevaluate Radon and Thoron Exposure in Gansu Province Study Using Radon-Thoron Discriminating Measurement Technique

Although the epidemiological studies provide evidence for an increased risk of lung cancer risk associated with residential radon, an issue of radon-thoron discrimination remains to be solved. In this study, an updated evaluation of lung cancer risk among the residents in Gansu, China was performed where one of the major epidemiological studies on indoor radon demonstrated an increased risk of lung cancer. We analyzed data from a hospital-based case-control study that included 30 lung cancer cases and 39 controls with special attention to internal exposure assessment based on the discriminative measurement technique of radon isotopes. Results from the analyses showed non-significant increased lung cancer risks; odds ratios (ORs) adjusted for age, smoking, and total income were 0.35 (95% CI: 0.07–1.74) and 0.27 (95% CI: 0.04–1.74) for groups living in residences with indoor radon concentrations of 50–100 Bq m⁻³ and over 100 Bq m⁻³, respectively, compared with those with < 50 Bq m⁻³ indoor radon concentrations. Although the small sample size hampers the usefulness of present analyses, our study suggests that reevaluation of lung cancer risk associated with residential radon in the epidemiological studies will be required on the basis of precise exposure assessment.

Bias correction for estimates from linear excess relative risk models in small case-control studies

Epidemiologic studies conducted to quantify the impact of radiation dose d on an outcome typically model the hazard ratio (HR) for association using a linear term, HR ( d ) = 1 + β d , via a linear excess relative risk (ERR) model, based on biological considerations. To study associations of risk of a second cancer with radiation treatment for a first cancer, several nested case-control designs to estimate β have been proposed that use refined doses received by different locations in the organ of interest. Here we first evaluated the small sample bias in maximum likelihood estimates of β for the linear ERR model using location-specific radiation doses in simulations. As we found substantial upward bias for studies of realistic sample sizes (more than 50% relative bias for studies with 75 cases), we also proposed and investigated several approaches to correct this bias. We studied first and second order jackknife bias corrections and we derived a modified set of score functions under retrospective case-control sampling, from which we directly obtained bias-corrected estimates. In simulations based on doses from a study of stomach cancer among testicular cancer survivors and synthetically generated data, neither the first nor second order jackknife bias correction performed well. Estimates based on the modified score equations corrected the bias much better, albeit not completely, and were numerically much more stable.

Systematic review and meta-analysis of residential radon and lung cancer in never-smokers

Background

Globally, radon is the leading risk factor for lung cancer in never-smokers (LCINS). In this study, we systematically reviewed and meta-analysed the evidence of the risk of LCINS associated with residential radon exposure.

Methods

Medline and Embase databases were searched using predefined inclusion and exclusion criteria to identify relevant studies published from 1 January 1990 to 5 March 2020 focused on never-smokers. We identified four pooled collaborative studies (incorporating data from 24 case–control studies), one case–control study and one cohort study for systematic review. Meta-analysis was performed on the results of the four pooled studies due to different measures of effect and outcome reported in the cohort study and insufficient information reported for the case–control study. In a post hoc analysis, the corresponding risk for ever-smokers was also examined.

Results

Risk estimates of lung cancer from residential radon exposure were pooled in the meta-analysis for 2341 never-smoker cases, 8967 never-smoker controls, 9937 ever-smoker cases and 12 463 ever-smoker controls. Adjusted excess relative risks (aERRs) per 100 Bq·m⁻³ of radon level were 0.15 (95% CI 0.06–0.25) for never-smokers and 0.09 (95% CI 0.03–0.16) for ever-smokers, and the difference between them was statistically insignificant (p=0.32). The aERR per 100 Bq·m⁻³was higher for men (0.46; 95% CI 0.15–0.76) than for women (0.09; 95% CI −0.02–0.20) among never-smokers (p=0.027).

Conclusion

This study provided quantified risk estimates for lung cancer from residential radon exposure among both never-smokers and ever-smokers. Among never-smokers in radon-prone areas, men were at higher risk of lung cancer than women.

Globally, radon is the leading cause of lung cancer in never-smokers. Yet its quantified link with lung cancer risk among never-smokers is not known. This study computes the risk estimate of lung cancer from residential radon exposure among never-smokers.https://bit.ly/32frCbq

Measurement of Indoor Thoron Gas Concentrations Using a Radon-Thoron Discriminative Passive Type Monitor: Nationwide Survey in Japan

As part of a nationwide survey of thoron (220Rn) in Japan, the indoor 220Rn gas concentrations in 940 dwellings were measured throughout one year, from 1993 to 1996, using a passive type 222Rn-220Rn discriminative monitor. The monitor was placed in a bedroom or a living room in each house for four successive three-month periods. The mean annual indoor 220Rn concentration was estimated from the four measurements in each house. The arithmetic mean, the median and the geometric mean for indoor 220Rn concentrations in 899 dwellings were 20.1, 9.6 and 10.0 Bq m-3, respectively. The 220Rn concentrations exhibited a log-normal distribution. It was found that the 220Rn concentrations were dependent on the nature of the materials used for wall construction and also on the distance of measurement from the wall. Significant seasonal variations in the 220Rn concentration were not observed. It would seem that the nature of the wall material contributed to the increased indoor 220Rn concentrations.

Characteristics of Thoron (220Rn) and Its Progeny in the Indoor Environment

The present paper outlines characteristics of thoron and its progeny in the indoor environment. Since the half-life of thoron (²²⁰Rn) is very short (55.6 s), its behavior is quite different from the isotope radon (²²²Rn, half-life 3.8 days) in the environment. Analyses of radon and lung cancer risk have revealed a clearly positive relationship in epidemiological studies among miners and residents. However, there is no epidemiological evidence for thoron exposure causing lung cancer risk. In contrast to this, a dosimetric approach has been approved in the International Commission on Radiological Protection (ICRP) Publication 137, from which new dose conversion factors for radon and thoron progenies can be obtained. They are given as 16.8 and 107 nSv (Bq m^-3 h)^-1, respectively. It implies that even a small quantity of thoron progeny will induce higher radiation exposure compared to radon. Thus, an interest in thoron exposure is increasing among the relevant scientific communities. As measurement technologies for thoron and its progeny have been developed, they are now readily available. This paper reviews measurement technologies, activity levels, dosimetry and resulting doses. Although thoron has been underestimated in the past, recent findings have revealed that reassessment of risks due to radon exposure may need to take the presence of thoron and its progeny into account.

Statistical inferences from measured data on concentrations of naturally occurring radon, thoron, and decay products in Kumaun Himalayan belt

Regional averages of radon, thoron, and associated decay product concentration are reported to be higher than their respective global averages in recent studies conducted in Indian Himalayan belt. The present study explores another region in Indian Himalayan belt by conducting measurements of radon, thoron, and decay product's activity concentration in 92 dwellings of Bageshwar district. The year-long measurements were performed in all 3 seasons distinguishing dwellings as per their construction material. The average radon and thoron concentration for the study region was measured as 57 Bq/m³ and 66 Bq/m³, respectively. Analysis of the measured data in terms of seasonal effects and construction material led to well established inferences, i.e., higher concentration for mud houses and for winter season. In addition, the present study focuses on lesser probed statistical inferences. One of them is related to the appropriateness of frequency distribution function for the measured data and other dwells upon the correlation analysis of inter-related factors for high concentration cases. Three distribution functions (Lognormal, Weibull, and Gamma) were found to be following the trend of frequency distribution curve of the measured data. For mud houses in winter season, variations of radon/thoron concentration were attempted to correlate with mass/surface exhalation rate, emanation rate, and source term content. More than 80% of the dwellings of the study region were found to have gas and decay product's concentration levels, higher than the respective global average values. However, these values were mostly within the reference levels for residential environments. Nevertheless, this region requires further studies to pinpoint the causes for elevated levels and suggest simple remedial modifications if required.

Importance of Discriminative Measurement for Radon Isotopes and Its Utilization in the Environment and Lessons Learned from Using the RADUET Monitor

Radon (222Rn) and thoron (220Rn), sources of natural background radiation, have been the subjects of long-standing studies, including research into radon and thoron as major causes of lung cancer at domestic and international levels. In this regard, radon and thoron measurement studies have been widely conducted all over the world. Generally, the techniques used relate to passive nuclear track detectors. Some surveys have shown that passive monitors for radon are sensitive to thoron, and hence some measured results have probably overestimated radon concentrations. This study investigated radon and thoron measurements in domestic and international surveys using the passive radon-thoron discriminative monitor, commercially named RADUET. This paper attempts to provide an understanding of discriminative measurements of radon isotopes and to present an evidence-based roadmap.

Residential Radon and Histological Types of Lung Cancer: A Meta-Analysis of Case‒Control Studies

Epidemiological studies on residential radon exposure and the risk of histological types of lung cancer have yielded inconsistent results. We conducted a meta-analysis on this topic and updated previous related meta-analyses. We searched the databases of Cochrane Library, Embase, PubMed, Web of Science and Chinese National Knowledge Infrastructure for papers published up to 13 November 2018. The pooled odds ratio (OR) and 95% confidence interval (CI) were calculated using fixed and random effects models. Subgroup and dose‒response analyses were also conducted. This study was registered with PROSPERO (No. CRD42019127761). A total of 28 studies, which included 13,748 lung cancer cases and 23,112 controls, were used for this meta-analysis. The pooled OR indicated that the highest residential radon exposure was significantly associated with an increased risk of lung cancer (OR = 1.48, 95% CI = 1.26–1.73). All histological types of lung cancer were associated with residential radon. Strongest association with small-cell lung carcinoma (OR = 2.03, 95% CI = 1.52–2.71) was found, followed by adenocarcinoma (OR = 1.58, 95% CI = 1.31–1.91), other histological types (OR = 1.54, 95% CI = 1.11–2.15) and squamous cell carcinoma (OR = 1.43, 95% CI = 1.18–1.74). With increasing residential radon levels per 100 Bq/m³, the risk of lung cancer, small-cell lung carcinoma and adenocarcinoma increased by 11%, 19% and 13%, respectively. This meta-analysis provides new evidence for a potential relationship between residential radon and all histological types of lung cancer.

Health Effects of Radon Exposure

Radon is a naturally occurring radioactive material that is formed as the decay product of uranium and thorium, and is estimated to contribute to approximately half of the average annual natural background radiation. When inhaled, it damages the lungs during radioactive decay and affects the human body. Through many epidemiological studies regarding occupational exposure among miners and residential exposure among the general population, radon has been scientifically proven to cause lung cancer, and radon exposure is the second most common cause of lung cancer after cigarette smoking. However, it is unclear whether radon exposure causes diseases other than lung cancer. Media reports have often dealt with radon exposure in relation to health problems, although public attention has been limited to a one-off period. However, recently in Korea, social interest and concern about radon exposure and its health effects have increased greatly due to mass media reports of high concentrations of radon being released from various close-to-life products, such as mattresses and beauty masks. Accordingly, this review article is intended to provide comprehensive scientific information regarding the health effects of radon exposure.

Lung cancer and residential radon in never-smokers: A pooling study in the Northwest of Spain

BACKGROUND

Using a pooled case-control study design, including only never-smokers, we have assessed the association of residential radon exposure with the subsequent occurrence of lung cancer. We also investigated whether residential radon poses a different risk specifically for adenocarcinoma.

METHODS

We pooled individual data from different case-control studies conducted in recent years in Northwestern Spain which investigated residential radon and lung cancer. All participants were never-smokers. Cases had a confirmed biopsy of primary lung cancer. Hospital controls were selected at pre-surgery units, presenting for non-complex surgical procedures. They were interviewed using a standardized instrument. Residential radon was measured using alpha track detectors at the Galician Radon Laboratory at the University of Santiago de Compostela.

RESULTS

A total of 1415 individuals, 523 cases and 892 controls were included. We observed an odds ratio of 1.73 (95%CI: 1.27-2.35) for individuals exposed to ≥ 200 Bq/m³ compared with those exposed to ≤100 Bq/m³. Lung cancer risk for adenocarcinoma was 1.52 (95%CI: 1.14-2.02) using the same categories for radon exposure.

CONCLUSIONS

Residential radon is a clear risk factor for lung cancer in never-smokers. Our data suggest that radon exposure is associated with all histological types of lung cancer and also with adenocarcinoma, which is currently the most frequent histological type for this disease.

Meta-analysis of case-control studies on the relationship between lung cancer and indoor radon exposure

Indoor exposure to natural radon is a factor that influences lung cancer risk worldwide. The present study includes a meta-analysis of epidemiological data on the relationship between lung cancer and indoor radon. Altogether, 31 case-control studies with 20,703 cases, 34,518 controls and 140 individual odds ratio (OR) estimates are included in the meta-analysis. Weighted median OR was calculated for five radon intervals. The following parameters were used for the weighting: standard error of OR, duration of radon concentration measurement, and relative number of controls in reference intervals. The dependence of the weighted median OR on the radon concentration was estimated applying linear non-threshold and threshold models. The results obtained suggest a significant linear no-threshold exposure-effect relationship for radon concentrations above 100 Bq/m³, with a slope of 0.14 (95% confidence interval 0.08-0.21) per 100 Bq/m³.

Meta-analysis of thirty-two case-control and two ecological radon studies of lung cancer

A re-analysis has been carried out of thirty-two case-control and two ecological studies concerning the influence of radon, a radioactive gas, on the risk of lung cancer. Three mathematically simplest dose-response relationships (models) were tested: constant (zero health effect), linear, and parabolic (linear-quadratic). Health effect end-points reported in the analysed studies are odds ratios or relative risk ratios, related either to morbidity or mortality. In our preliminary analysis, we show that the results of dose-response fitting are qualitatively (within uncertainties, given as error bars) the same, whichever of these health effect end-points are applied. Therefore, we deemed it reasonable to aggregate all response data into the so-called Relative Health Factor and jointly analysed such mixed data, to obtain better statistical power. In the second part of our analysis, robust Bayesian and classical methods of analysis were applied to this combined dataset. In this part of our analysis, we selected different subranges of radon concentrations. In view of substantial differences between the methodology used by the authors of case-control and ecological studies, the mathematical relationships (models) were applied mainly to the thirty-two case-control studies. The degree to which the two ecological studies, analysed separately, affect the overall results when combined with the thirty-two case-control studies, has also been evaluated. In all, as a result of our meta-analysis of the combined cohort, we conclude that the analysed data concerning radon concentrations below ~1000 Bq/m3 (~20 mSv/year of effective dose to the whole body) do not support the thesis that radon may be a cause of any statistically significant increase in lung cancer incidence.

Logistic regression model for detecting radon prone areas in Ireland

A new high spatial resolution radon risk map of Ireland has been developed, based on a combination of indoor radon measurements (n=31,910) and relevant geological information (i.e. Bedrock Geology, Quaternary Geology, soil permeability and aquifer type). Logistic regression was used to predict the probability of having an indoor radon concentration above the national reference level of 200Bqm^-3 in Ireland. The four geological datasets evaluated were found to be statistically significant, and, based on combinations of these four variables, the predicted probabilities ranged from 0.57% to 75.5%. Results show that the Republic of Ireland may be divided in three main radon risk categories: High (HR), Medium (MR) and Low (LR). The probability of having an indoor radon concentration above 200Bqm^-3 in each area was found to be 19%, 8% and 3%; respectively. In the Republic of Ireland, the population affected by radon concentrations above 200Bqm^-3 is estimated at ca. 460k (about 10% of the total population). Of these, 57% (265k), 35% (160k) and 8% (35k) are in High, Medium and Low Risk Areas, respectively. Our results provide a high spatial resolution utility which permit customised radon-awareness information to be targeted at specific geographic areas.

Radon-induced lung cancer deaths may be overestimated due to failure to account for confounding by exposure to diesel engine exhaust in BEIR VI miner studies

BACKGROUND

EPA reported that radon is the second leading cause of lung cancer in the United States, killing 21,100 people per year. EPA relies on the BEIR VI models, based on an evaluation of radon exposure and lung cancer risk in studies of miners. But these models did not account for co-exposure to diesel exhaust, a known human carcinogen recently classified by IARC. It is probable then that a portion of the lung cancer deaths in the miner cohorts are originally attributable to the exposure to diesel rather than radon.

OBJECTIVE

To re-evaluate EPA's radon attributable lung cancer estimates accounting for diesel exposure information in the miner cohorts.

METHODS

We used estimates of historical diesel concentrations, combined with diesel exposure-response functions, to estimate the risks of lung cancer attributable to diesel engine exhaust (DEE) exposure in the miner studies. We re-calculated the fatal lung cancer risk attributable to radon after accounting for risk from diesel and re-estimated the number of U.S. deaths associated with radon in the U.S. using EPA's methodology.

RESULTS

Considering the probable confounding with DEE exposure and using the same estimate of baseline mortality from 1989-91 that the EPA currently uses in their calculations, we estimate that radon-induced lung cancer deaths per year are 15,600 (95% CI: 14,300, 17,000)- 19,300 (95% CI: 18,800, 20,000) in the U.S. population, a reduction of 9%-26%. The death estimates would be 12,900-15,900 using 2014 baseline vital statistics.

CONCLUSIONS

We recommend further research on re-evaluating the health effects of exposure to radon that accounts for new information on diesel exhaust carcinogenicity in BEIR VI models, up-to-date vital statistics and new epidemiological evidence from residential studies.

An updated review of case-control studies of lung cancer and indoor radon-Is indoor radon the risk factor for lung cancer?

Lung cancer is a leading cause of cancer-related death in the world. Smoking is definitely the most important risk factor for lung cancer. Radon (²²²Rn) is a natural gas produced from radium (²²⁶Ra) in the decay series of uranium (²³⁸U). Radon exposure is the second most common cause of lung cancer and the first risk factor for lung cancer in never-smokers.

Case–control studies have provided epidemiological evidence of the causative relationship between indoor radon exposure and lung cancer. Twenty-four case–control study papers were found by our search strategy from the PubMed database. Among them, seven studies showed that indoor radon has a statistically significant association with lung cancer. The studies performed in radon-prone areas showed a more positive association between radon and lung cancer. Reviewed papers had inconsistent results on the dose–response relationship between indoor radon and lung cancer risk.

Further refined case–control studies will be required to evaluate the relationship between radon and lung cancer. Sufficient study sample size, proper interview methods, valid and precise indoor radon measurement, wide range of indoor radon, and appropriate control of confounders such as smoking status should be considered in further case–control studies.

Lung cancer in never-smokers: a case-control study in a radon-prone area (Galicia, Spain)

The aim of the study was to assess the effect of residential radon exposure on the risk of lung cancer in never-smokers and to ascertain if environmental tobacco smoke modifies the effect of residential radon. We designed a multicentre hospital-based case-control study in a radon-prone area (Galicia, Spain). All participants were never-smokers. Cases had an anatomopathologically confirmed primary lung cancer and controls were recruited from individuals undergoing minor, non-oncological surgery. Residential radon was measured using alpha track detectors. We included 521 individuals, 192 cases and 329 controls, 21% were males. We observed an odds ratio of 2.42 (95% CI 1.45-4.06) for individuals exposed to ≥200 Bq·m(-3) compared with those exposed to <100 Bq·m(-3). Environmental tobacco smoke exposure at home increased lung cancer risk in individuals with radon exposure>200 Bq·m(-3). Individuals exposed to environmental tobacco smoke and to radon concentrations>200 Bq·m(-3) had higher lung cancer risk than those exposed to lower radon concentrations and exposed to environmental tobacco smoke. Residential radon increases lung cancer risk in never-smokers. An association between residential radon exposure and environmental tobacco smoke on the risk of lung cancer might exist.

Residential radon and lung cancer in never smokers. A systematic review

Radon exposure is considered the second cause of lung cancer and the first in never smokers. We aim to assess the effect of residential radon exposure on the risk of lung cancer in never smokers through a systematic review applying predefined inclusion and exclusion criteria. 14 Studies were included. Some of them point to a relationship between residential radon and lung cancer while others show no association. Further studies are necessary to test this association and to assess if other risk factors such as environmental tobacco smoke could modify the effect of residential radon exposure on lung cancer.

Evidence of a paradoxical relationship between endotoxin and lung cancer after accounting for left truncation in a study of Chinese female textile workers

INTRODUCTION

Occupational exposure to endotoxin, found in Gram-negative bacteria in organic material, has been associated predominantly with a reduced risk of lung cancer among workers. An inverse exposure-response gradient among women textile workers in Shanghai, China, has been reported previously. In this case-cohort study, we investigated the influence of left truncation, which can itself induce a downward trend, on the observed association.

METHODS

Subjects were enrolled between 1989 and 1991 and followed until 1998. The data were left-truncated as all subjects were hired before baseline. An analysis was performed with 3038 subcohort members and 602 cases of incident lung cancer. To evaluate left truncation, we compared lung cancer rates in those hired longer ago with those hired more recently among unexposed subjects. Cox proportional hazards modelling was used to estimate incident rate ratios (IRRs) and 95% CIs.

RESULTS

Among those who were never exposed to workplace endotoxin, we compared lung cancer rates in those hired >35 years before enrolment with workers hired ≤35 years before enrolment and observed a reduced risk in the former group, IRR=0.74, 95% CI (0.51 to 1.07). After accounting for this downward bias from left truncation, the reduced risk associated with endotoxin remained among those hired ≤50 years before enrolment. In contrast, there was suggestion of an increased risk of lung cancer among those hired >50 years ago.

CONCLUSIONS

After examination of left truncation bias, an inverse dose-response between endotoxin and lung cancer remained for all subjects except those hired longest ago.

Residential radon and lung cancer risk: an updated meta- analysis of case-control studies

BACKGROUND

Numbers of epidemiological studies assessing residential radon exposure and risk of lung cancer have yielded inconsistent results.

METHODS

We therefore performed a meta-analysis of relevant published case- control studies searched in the PubMed database through July 2011 to examine the association. The combined odds ratio (OR) were calculated using fixed- or random-effects models. Subgroup and dose-response analyses were also performed.

RESULTS

We identified 22 case-control studies of residential radon and lung cancer risk involving 13,380 cases and 21,102 controls. The combined OR of lung cancer for the highest with the lowest exposure was 1.29 (95% CI 1.10-1.51). Dose-response analysis showed that every 100 Bq/m3 increment in residential radon exposure was associated with a significant 7% increase in lung cancer risk. Subgroup analysis displayed a more pronounced association in the studies conducted in Europe. Studies restricted to female or non-smokers demonstrated weakened associations between exposure and lung cancer.

CONCLUSIONS

This meta- analysis provides new evidence supporting the conclusion that residential exposure to radon can significantly increase the risk of lung cancer in a dose-response manner.

Residential radon and lung cancer incidence in a Danish cohort

High-level occupational radon exposure is an established risk factor for lung cancer. We assessed the long-term association between residential radon and lung cancer risk using a prospective Danish cohort using 57,053 persons recruited during 1993-1997. We followed each cohort member for cancer occurrence until 27 June 2006, identifying 589 lung cancer cases. We traced residential addresses from 1 January 1971 until 27 June 2006 and calculated radon at each of these addresses using information from central databases regarding geology and house construction. Cox proportional hazards models were used to estimate incidence rate ratios (IRR) and 95% confidence intervals (CI) for lung cancer risk associated with residential radon exposure with and without adjustment for sex, smoking variables, education, socio-economic status, occupation, body mass index, air pollution and consumption of fruit and alcohol. Potential effect modification by sex, traffic-related air pollution and environmental tobacco smoke was assessed. Median estimated radon was 35.8 Bq/m(3). The adjusted IRR for lung cancer was 1.04 (95% CI: 0.69-1.56) in association with a 100 Bq/m(3) higher radon concentration and 1.67 (95% CI: 0.69-4.04) among non-smokers. We found no evidence of effect modification. We find a positive association between radon and lung cancer risk consistent with previous studies but the role of chance cannot be excluded as these associations were not statistically significant. Our results provide valuable information at the low-level radon dose range.

Radon measurement in schools located in three priority investigation areas in the province of Quebec, Canada

The purpose of this study was to measure radon concentration in public primary schools located in priority investigation areas, with the aim of decreasing occupants' exposure to radon in public buildings where concentrations exceed the Canadian Federal guidelines (i.e. 200 Bq m(-3)). In addition, the association between radon levels, substratum geological characteristics and schools' structural characteristics were investigated. The results showed that radon concentrations measured in the 65 investigated schools are generally below the Federal guideline levels. Eleven schools (17 %) had at least one measurement above the Federal guideline, while one had a level above 600 Bq m(-3). On average, targeted schools' occupants are exposed to radon concentrations of 56 Bq m(-3). Although statistical analysis, which was limited by the sample size, did not show any link between aggregated radon measurements and geochemical or radiological signatures of investigated sites, the geological evidence that led to the choice of the studied regions remains relevant.

ICRP Publication 115. Lung cancer risk from radon and progeny and statement on radon

Recent epidemiological studies of the association between lung cancer and exposure to radon and its decay products are reviewed. Particular emphasis is given to pooled case-control studies of residential exposures, and to cohorts of underground miners exposed to relatively low levels of radon. The residential and miner epidemiological studies provide consistent estimates of the risk of lung cancer, with significant associations observed at average annual concentrations of approximately 200 Bq/m³ and cumulative occupational levels of approximately 50 working level months (WLM), respectively. Based on recent results from combined analyses of epidemiological studies of miners, a lifetime excess absolute risk of 5 × 10⁻⁴ per WLM [14 × 10⁻⁵ per (mJh/m³)] should now be used as the nominal probability coefficient for radon- and radon-progeny-induced lung cancer, replacing the previous Publication 65 (ICRP, 1993) value of 2.8 × 10⁻⁴ per WLM [8 × 10⁻⁵ per (mJh/m³)]. Current knowledge of radon-associated risks for organs other than the lungs does not justify the selection of a detriment coefficient different from the fatality coefficient for radon-induced lung cancer. Publication 65 (ICRP, 2003) recommended that doses from radon and its progeny should be calculated using a dose conversion convention based on epidemiological data. It is now concluded that radon and its progeny should be treated in the same way as other radionuclides within the ICRP system of protection; that is, doses from radon and its progeny should be calculated using ICRP biokinetic and dosimetric models. ICRP will provide dose coefficients per unit exposure to radon and its progeny for different reference conditions of domestic and occupational exposure, with specified equilibrium factors and aerosol characteristics.

Pooled Bayesian analysis of twenty-eight studies on radon induced lung cancers

The influence of ionizing radiation of (222)Rn and its progeny on lung cancer risks that were published in 28 papers was re-analyzed using seven alternative dose-response models. The risks of incidence and mortality were studied in two ranges of low annual radiation dose: 0-70 mSv per year (391 Bq m(-3)) and 0-150 mSv per year (838 Bq m(-3)). Assumption-free Bayesian statistical methods were used. The analytical results demonstrate that the published incidence and mortality data do not show that radiation dose is associated with increased risk in this range of doses. This conclusion is based on the observation that the model assuming no dependence of the lung cancer induction on the radiation doses is at least ∼90 times more likely to be true than the other models tested, including the linear no-threshold (LNT) model.

Thoron in indoor air: modeling for a better exposure estimate

Only recently, the radioactive gas thoron ((220)Rn) and its decay products have been regarded as significant health risk in the indoor environment. This is because of new findings of increased thoron concentrations in traditional mud dwellings and considerations leading toward reduced action levels for natural airborne radionuclides. A model which describes the sources and sinks of thoron and its decay products should help to assess the indoor exposure. This work presents an extensive depiction of the influences of indoor conditions on the occurrence of these radionuclides. Measurements were performed in an experiment room and in mud dwellings in China and India. Mud even with an average (232)Th concentration was identified as a significant thoron source. The spatial distribution of the decay products proved to be homogeneous, which is in contrast to thoron gas. The prominent contribution of the unattached and attached decay product (212)Pb to the exposure was elaborated. The theoretically derived impact of air exchange and aerosol concentration, which determines the proportion of unattached decay products, could be confirmed. Transfer coefficients of the model were determined. The thoron model with these transfer coefficients predicts annual doses of almost 2 mSv for dwellers of traditional Chinese and Indian mud buildings, confirming the potential health impact of thoron.

PRACTICAL IMPLICATIONS

The radioactive noble gas radon with its decay products is well known as a health risk. After increased concentrations of the isotope (220)Rn (thoron) have been found in traditional Chinese mud-walled cave dwellings, the need for a model that describes the occurrence of thoron and its decay products indoors has arisen. This work presents such a model from the emergence of thoron in the building material until the decay to the stable (208)Pb and discusses the various influences on the occurrence of these nuclides. The model makes possible to predict the exposure of people staying in a room to thoron and its decay products and--combined with a dose model--to calculate their inhalation doses from easily measurable data.

Lauriston S. Taylor lecture: radiation epidemiology--the golden age and future challenges

Epidemiology is the study of the distribution and causes of disease in humans. Studies of human populations exposed to ionizing radiation have been conducted for nearly 100 y during the "Golden Age of Radiation Epidemiology." Radiation epidemiology is now so sophisticated that human studies are the basis for radiation protection standards and for compensation schemes in response to claims of ill health from prior exposures. The studies of exposed human populations are very broad and include not only the Japanese atomic bomb survivors, but also patients given radiotherapy for cancer, patients treated with radiation for nonmalignant disease, patients given diagnostic radiation, persons with intakes of radionuclides, workers exposed to occupational radiation, and communities exposed to environmental sources of radiation. But there is more to be learned, and future knowledge may be advanced from new and continued occupational studies of the early radiation workers, atomic veterans, medically exposed patients, and populations living in areas of high natural background radiation. The interaction between radiation and underlying genetic susceptibilities is an important emerging area of research. It is indeed an honor to be included among the Lauriston S. Taylor Lecturers.

Low-dose Photon and Simulated Solar Particle Event Proton Effects on Foxp3+ T Regulatory Cells and other Leukocytes

Radiation is a major factor in the spaceflight environment that has carcinogenic potential. Astronauts on missions are continuously exposed to low-dose/low-dose-rate (LDR) radiation and may receive relatively high doses during a solar particle event (SPE) that consists primarily of protons. However, there are very few reports in which LDR photons were combined with protons. In this study, C57BL/6 mice were exposed to 1.7 Gy simulated SPE (sSPE) protons over 36 h, both with and without pre-exposure to 0.01 Gray (Gy) LDR γ-rays at 0.018 cGy/h. Apoptosis in skin samples was determined by immunohistochemistry immediately post-irradiation (day 0). Spleen mass relative to body mass, white blood cells (WBC), major leukocyte populations, lymphocyte subsets (T, Th, Tc, B, NK), and CD4+ CD25+ Foxp3+ T regulatory (Treg) cells were analyzed on days 4 and 21. Apoptosis in skin samples was evident in all irradiated groups; the LDR+sSPE mice had the greatest expression of activated caspase-3. On day 4 post-irradiation, the sSPE and LDR+sSPE groups had significantly lower WBC counts in blood and spleen compared to non-irradiated controls ( p < 0.05 vs. 0 Gy). CD4+ CD25+ Foxp3+ Treg cell numbers in spleen were decreased at day 4, but proportions were increased in the sSPE and LDR+sSPE groups ( p < 0.05 vs. 0 Gy). By day 21, lymphocyte counts were still low in blood from the LDR+sSPE mice, especially due to reductions in B, NK, and CD8+ T cytotoxic cells. The data demonstrate, for the first time, that pre-exposure to LDR photons did not protect against the adverse effects of radiation mimicking a large solar storm. The increased proportion of immunosuppressive CD4+ CD25+ Foxp3+ Treg and persistent reduction in circulating lymphocytes may adversely impact immune defenses that include removal of sub-lethally damaged cells with carcinogenic potential, at least for a period of time post-irradiation.

Why is 220Rn (thoron) measurement important?

New scientific findings based on the latest epidemiological analyses for lung cancer risk due to radon have been demonstrated. The residential radon concentration is mainly measured by passive radon detectors. Although the passive radon detector is usually designed to detect radon efficiently and exclusively, several types of them can detect thoron together with radon. In this case, these detector readings may include both radon and thoron signals. If the readings are overestimated, the lung cancer risk will be given as a biased estimate when epidemiological studies are carried out. In our experience, there seem to be no correlation among radon, thoron and thoron progeny concentrations. Therefore, one parameter cannot be estimated by the other. This study presents the importance of thoron measurement throughout results we have obtained in field and in laboratory so far.

Thoron: its metrology, health effects and implications for radon epidemiology: a summary of roundtable discussions

A roundtable discussion was made at the end of the workshop. All the presentations were summarised in this discussion. It involved measurement techniques, quality assurance and dose assessment and health effects of thoron and its progeny. In particular, major epidemiological studies may be affected by thoron interference in radon measurements. Since their data are not sufficient when compared with that of radon, further efforts in thoron studies will be needed.

Human Lung Cancer Risks from Radon - Part III - Evidence of Influence of Combined Bystander and Adaptive Response Effects on Radon Case-Control Studies - A Microdose Analysis

Since the publication of the BEIR VI (1999) report on health risks from radon, a significant amount of new data has been published showing various mechanisms that may affect the ultimate assessment of radon as a carcinogen, in particular the potentially deleterious Bystander Effect (BE) and the potentially beneficial Adaptive Response radio-protection (AR). The case-control radon lung cancer risk data of the pooled 13 European countries radon study (Darby et al 2005, 2006) and the 8 North American pooled study (Krewski et al 2005, 2006) have been evaluated. The large variation in the odds ratios of lung cancer from radon risk is reconciled, based on the large variation in geological and ecological conditions and variation in the degree of adaptive response radio-protection against the bystander effect induced lung damage. The analysis clearly shows Bystander Effect radon lung cancer induction and Adaptive Response reduction in lung cancer in some geographical regions. It is estimated that for radon levels up to about 400 Bq m(-3) there is about a 30% probability that no human lung cancer risk from radon will be experienced and a 20% probability that the risk is below the zero-radon, endogenic spontaneous or perhaps even genetically inheritable lung cancer risk rate. The BEIR VI (1999) and EPA (2003) estimates of human lung cancer deaths from radon are most likely significantly excessive. The assumption of linearity of risk, by the Linear No-Threshold Model, with increasing radon exposure is invalid.

Lung cancer in Chinese women: evidence for an interaction between tobacco smoking and exposure to inhalants in the indoor environment

BACKGROUND

Epidemiologic data suggest that Chinese women have a high incidence of lung cancer in relation to their smoking prevalence. In addition to active tobacco smoke exposure, other sources of fumes and airborne particles in the indoor environment, such as cooking and burning of incense and mosquito coils, have been considered potential risk factors for lung cancer.

OBJECTIVES

We used a case-control study to explore effects of inhalants from combustion sources common in the domestic environment on lung cancer and their modification by active tobacco smoking.

METHODS

We analyzed 703 primary lung cancer cases and 1,578 controls. Data on demographic background and relevant exposures were obtained by face-to-face interviews in the hospital.

RESULTS

We observed a positive relationship with daily exposure to incense or mosquito coils and to cooking fumes only among smokers, and no association among lifetime nonsmokers. Interactions between smoking and frequency of cooking, or exposure to incense or mosquito coils were statistically significant and consistent with synergistic effects on lung cancer. The odds ratio (OR) comparing smokers without daily incense or mosquito coil exposure with nonsmokers without daily exposure was 2.80 [95% confidence interval (CI), 1.86-4.21], whereas the OR comparing smokers with daily exposure to the same referent group was 4.61 (95% CI, 3.41-6.24). In contrast, daily exposure to incense or mosquito coils was not associated with lung cancer among nonsmokers (OR = 0.91; 95% CI, 0.72-1.16). We observed the same pattern of associations for smokers without (OR = 2.31; 95% CI, 1.52-3.51) and with (OR = 4.50; 95% CI, 3.21-6.30) daily cooking exposure compared with nonsmokers, with no evidence of an association with daily cooking exposure among nonsmokers.

CONCLUSION

Our results suggest that active tobacco smoking not only is an important risk factor for development of lung cancer, but also may cause smokers to be more susceptible to the risk-enhancing effects of other inhalants.

Risk factors for lung cancer: a case-control study in Hong Kong women

To identify etiological connections of lung cancer in Chinese women in Hong Kong, who are among the highest in lung cancer incidence and mortality, we conducted a case-control study, in which 279 female lung cancer cases and 322 controls were selected and frequency matched. A variety of information, including dietary habits, occupational history, smoking, domestic environmental exposures, and family history of cancer was collected, and their associations with lung cancer were analyzed with logistic analysis approach. In addition to positive associations with exposures to cooking emissions and to radon at home, smoking and family cancer history, we observed that increasing consumption of meat was linked to a higher risk, whereas consumptions of vegetables had a strong protective effect against lung cancer. Moderate consumption of coffee appeared to be beneficial against the disease. Those never employed and domestic helpers were at a higher risk. The results indicated that environmental exposures, risky personal behaviors, or lifestyle, as well as family cancer aggregation are among important contributors to the high incidence of lung cancer in Hong Kong females.

Immunological mechanism of the low-dose radiation-induced suppression of cancer metastases in a mouse model

According to the doctrine underlying the current radiation protection regulations each, no matter how small, exposure to ionizing radiation may be carcinogenic. However, numerous epidemiological observations demonstrate that cancer incidence and/or mortality are not elevated among inhabitants of the high- versus low-natural-background radiation areas and homes. Results of our own and other authors' studies described in this paper bear testimony to the possibility that stimulation of the anti-neoplastic immune surveillance mediated by NK lymphocytes and activated macrophages explains, at least partially, the accumulating epidemiological and experimental evidence indicating that low-level exposures to the low-linear energy transfer (LET) radiation inhibit the development of spontaneous and artificial metastases in humans and laboratory animals, respectively. The results presented also suggest the possibility of using low-level X- and gamma-ray exposures to cure cancer and to prevent cancer metastases. For a broader perspective, the results presented may help towards relaxing the current radiation protection regulations, especially as they apply to diagnostic and therapeutic exposures of patients to the indicated forms of radiation.

The impact of dosimetry uncertainties on dose-response analyses

Radiation dose estimates used in epidemiological studies are subject to many sources of uncertainty, and the error structure may be a complicated mixture of different types of error. Increasingly, efforts are being made to evaluate dosimetry uncertainties and to take account of them in statistical analyses. The impact of these uncertainties on dose-response analyses depends on the magnitude and type of error. Errors that are independent from subject to subject (random errors) reduce statistical power for detecting a dose-response relationship, increase uncertainties in estimated risk coefficients, and may lead to underestimation of risk coefficients. The specific effects of random errors depend on whether the errors are "classical" or "Berkson." Classical error can be thought of as error that arises from an imprecise measuring device, whereas Berkson error occurs when a single dose is used to represent a group of subjects (with varying true doses). Uncertainties in quantities that are common to some or all subjects are "shared" uncertainties. Such uncertainties increase the possibility of bias, and accounting for this possibility increases the length of confidence intervals. In studies that provide a direct evaluation of risk at low doses and dose rates, dosimetry errors are more likely to mask a true effect than to create a spurious one. In addition, classical errors and shared dosimetry uncertainties increase the potential for bias in estimated risks coefficients, but this potential may already be large due to the extreme vulnerability to confounding in studies involving very small relative risk.

A simulation study of radon and thoron discrimination problem in case-control studies

In most countries, radon is the dominant contributor among natural radiation sources to the radiation exposure dose of the general population. Numerous case-control studies of residential radon and lung cancer have been conducted using passive radon (Rn-222) detectors. These studies showed that radon may increase lung cancer risk, but most of them did not show a significant risk. Recently it was shown that the readings of passive radon detectors that do not employ thoron (Rn-220) discrimination techniques are affected by thoron. Therefore, we conducted a simulation study to evaluate the possible effect of thoron interference on the estimation of radon-related lung cancer risk. Various assumptions were made based on the number of cases, matching ratio, baseline risk, true radon-related risk, distribution of radon and thoron concentrations, correlation between radon and thoron, and radon detectors. The results suggested that in certain circumstances thoron interference in radon measurements resulted in an approximately 90% downward bias. In addition, the magnitude of the bias increased as the geometric mean and geometric standard error of radon concentration decreased and those of thoron increased. In order to resolve this problem, it is necessary to use passive radon detectors with thoron discrimination techniques in epidemiological studies.

Health effects of radon: a review of the literature

PURPOSE

Radon is natural radioactive noble gas that can be found in soil, water, outdoor and indoor air. Exposure to radon accounts for more that 50% of the annual effective dose of natural radioactivity. The purpose of the current review is to summarize recent literature and evaluate the weight of evidence on the adverse health effects of radon.

CONCLUSIONS

Radon is an established human lung carcinogen based on human epidemiological data supported by experimental evidence of mutagenesis studies in cell culture and laboratory animals. Extrapolation from cohort studies on miners suggested that radon is the second leading cause of lung cancer death after tobacco smoke. The majority of studies on the relationship between radon and other types of cancers showed weak or no association. Low levels of radon can be found in drinking water; however, radon released during water usage adds small quantities to indoor radon concentration. Studies showed that the risk of stomach cancer and other gastrointestinal malignancies from radon in drinking water is small. Studies of the genetic and cytogenetic effects of indoor radon yielded equivocal results; while radon exposure in miners induces gene mutations and chromosomal aberrations. Numerous in vitro cytogenetic studies demonstrated that radon induces different types of genetic and cytogenetic damage that is likely to play a role in radon lung carcinogenesis.

Measurement error in the explanatory variable of a binary regression: regression calibration and integrated conditional likelihood in studies of residential radon and lung cancer

In epidemiology, one approach to investigating the dependence of disease risk on an explanatory variable in the presence of several confounding variables is by fitting a binary regression using a conditional likelihood, thus eliminating the nuisance parameters. When the explanatory variable is measured with error, the estimated regression coefficient is biased usually towards zero. Motivated by the need to correct for this bias in analyses that combine data from a number of case-control studies of lung cancer risk associated with exposure to residential radon, two approaches are investigated. Both employ the conditional distribution of the true explanatory variable given the measured one. The method of regression calibration uses the expected value of the true given measured variable as the covariate. The second approach integrates the conditional likelihood numerically by sampling from the distribution of the true given measured explanatory variable. The two approaches give very similar point estimates and confidence intervals not only for the motivating example but also for an artificial data set with known properties. These results and some further simulations that demonstrate correct coverage for the confidence intervals suggest that for studies of residential radon and lung cancer the regression calibration approach will perform very well, so that nothing more sophisticated is needed to correct for measurement error.

Radon survey in dwellings of Gansu, China: the influence of thoron and an attempt for correction

Alpha track detectors used in a previous investigation of the US National Cancer Institute and the China Ministry of Health on indoor radon ((222)Rn) in Gansu, China, proved to be influenced by (220)Rn (thoron), thus overestimating the (222)Rn level. Therefore, the detector was improved used in the previous survey. The new detectors allow discrimination between the two isotopes without any disturbance of the (222)Rn measurement. With this detector, a semi-annual study was conducted in 49 traditional dwellings of a village in Gansu. The arithmetic (AM) and geometric (GM) mean (222)Rn concentrations were 120 +/- 61 and 105 Bq m(-3) (with geometric standard deviation GSD = 1.8), respectively, while the mean (220)Rn concentrations at 2.5 cm wall distance were 430 +/- 210 Bq m(-3) (AM) and 350 Bq m(-3) (GM) with GSD = 2.3. The high thoron concentrations demonstrate the importance of the (220)Rn contribution to radiation exposure, in the investigated area. The actual level of indoor (222)Rn was about three times lower than that in the previous investigation which was affected by (220)Rn. A correction method for the radon results of the previous study is proposed, which provides (222)Rn and (220)Rn values comparable with those obtained in the study presented here.

Are cancer risks associated with exposures to ionising radiation from internal emitters greater than those in the Japanese A-bomb survivors?

After ingestion or inhalation of radionuclides, internal organs of the human body will be exposed to ionising radiation. Current risk estimates of radiation-associated cancer from internal emitters are largely based on extrapolation of risk from high-dose externally exposed groups. Concerns have been expressed that extrapolated risk estimates from internal emitters are greatly underestimated, by factors of ten or more, thus implying a severe underestimation of the true risks. Therefore, data on cancer mortality and incidence in a number of groups who received exposure predominantly from internal emitters are examined and excess relative risks per Sv are compared with comparable (age at exposure, time since exposure, gender) matched subsets of the Japanese atomic bomb survivor cohort. Risks are examined separately for low LET and high LET internal emitters. There are eight studies informative for the effects of internal low LET radiation exposure and 12 studies informative for the effects of internal high LET radiation. For 11 of the 20 cancer endpoints (subgroups of particular study cohorts) examined in the low LET internal emitter studies, the best estimate of the excess relative risk is greater than the corresponding estimate in the Japanese atomic bomb survivors and for the other nine it is less. For four of these 20 studies, the relative risk is significantly (2-sided P < 0.05) different from that in the Japanese atomic bomb survivors, in three cases greater than the atomic bomb survivor relative risk and in one case less. Considering only those six low LET studies/endpoints with 100 or more deaths or cases, for four out of six studies/endpoints the internal emitter risk is greater than that in the Japanese atomic bomb survivors. For seven of the 24 cancer endpoints examined in the high LET internal emitter studies the best estimate of the ERR in the internal emitter study is greater than the corresponding estimate in the Japanese atomic bomb survivors and for the other 17 it is less. For six studies, the relative risk is significantly (2-sided P < 0.05) different from that in the Japanese atomic bomb survivors, in one case greater than the atomic bomb survivor relative risk and in five cases less. Considering only those eight high LET studies/endpoints with 100 or more deaths or cases, for five out of eight studies/endpoints the internal emitter risk is greater than that in the Japanese atomic bomb survivors. These results suggest that excess relative risks in the internal emitter studies do not appreciably differ from those in the Japanese atomic bomb survivors. However, there are substantial uncertainties in estimates of risks in the internal emitter studies, particularly in relation to lung cancer associated with radon daughter (alpha particle) exposure, so a measure of caution should be exercised in these conclusions.

Adverse effects attributed to long-term radon inhalation in rats

The aim of this study was to investigate the adverse effect of long-term radon exposure on lung and blood cells in rats exposed to different radiation doses. Sprague-Dawley rats were exposed to radon for cumulative doses up to 66, 111, and 174 WLM (work level month). Total number and differential cells counts were determined in the bronchoalveolar lavage fluid (BALF) and the peripheral blood, as well as the activity of lactate dehydrogenase (LDH) and levels of glutathione (GSH) and total protein. DNA damage and interleukin (IL)-6 mRNA expression in BALF cells and peripheral blood mononuclear cells (PBMC) were detected by single cell gel electrophoresis (SCGE) and reverse-transcription polymerase chain reaction (RT-PCR), respectively. The results showed that radon-exposed lymphocytes were significantly lower and granulocytes higher in BALF compared to blood in exposed groups. The distance of DNA migration in the BALF and PBMC increased in a dose-dependent manner. A positive correlation between the PBMC and BALF cells in terms of DNA damage was noted. These findings suggested that PBMC might be used as a surrogate for BALF cells and thus the easier non-invasive ability to obtain PBMC may be useful in detection of lung DNA damage induced by radon.

Smoking and hormesis as confounding factors in radiation pulmonary carcinogenesis

Confounding factors in radiation pulmonary carcinogenesis are passive and active cigarette smoke exposures and radiation hormesis. Significantly increased lung cancer risk from ionizing radiation at lung doses < 1 Gy is not observed in never smokers exposed to ionizing radiations. Residential radon is not a cause of lung cancer in never smokers and may protect against lung cancer in smokers. The risk of lung cancer found in many epidemiological studies was less than the expected risk (hormetic effect) for nuclear weapons and power plant workers, shipyard workers, fluoroscopy patients, and inhabitants of high-dose background radiation. The protective effect was noted for low- and mixed high- and low-linear energy transfer (LET) radiations in both genders. Many studies showed a protection factor (PROFAC) > 0.40 (40% avoided) against the occurrence of lung cancer. The ubiquitous nature of the radiation hormesis response in cellular, animal, and epidemio-logical studies negates the healthy worker effect as an explanation for radiation hormesis. Low-dose radiation may stimulate DNA repair/apoptosis and immunity to suppress and eliminate cigarette-smoke-induced transformed cells in the lung, reducing lung cancer occurrence in smokers.

Some statistical implications of dose uncertainty in radiation dose-response analyses

Statistical dose-response analyses in radiation epidemiology can produce misleading results if they fail to account for radiation dose uncertainties. While dosimetries may differ substantially depending on the ways in which the subjects were exposed, the statistical problems typically involve a predominantly linear dose-response curve, multiple sources of uncertainty, and uncertainty magnitudes that are best characterized as proportional rather than additive. We discuss some basic statistical issues in this setting, including the bias and shape distortion induced by classical and Berkson uncertainties, the effect of uncertain dose-prediction model parameters on estimated dose-response curves, and some notes on statistical methods for dose-response estimation in the presence of radiation dose uncertainties.