High-LET Radiation: Radon
Radon is an inert gas produced naturally from radium in the decay series of uranium. Two of the radon decay products emit alpha particles that can, consequent to high energy and mass, cause damage to the DNA of cells of the respiratory epithelium. Epidemiologic studies of underground miners of uranium and other ores have established exposure to radon daughters as a cause of lung cancer. In the underground miners exposed to radon in past centuries, very high lung cancer risks were observed; in the miners in more contemporary workplaces, the observed risks have been much less as exposure concentrations have been better controlled, but still show clear evidence of existing cancer risk. Cigarette smoking and radon decay products synergistically influence lung cancer risk, for example, in a manner that is greater than simply adding the risks of each together. For this reason, the bulk of the lung cancer burden caused by radon exposure in the general population is concentrated within cigarette smokers.
Radon is of broader societal interest because it is a ubiquitous air pollutant that enters buildings from the underlying soil. On average, indoor exposures to radon for the general population are much less than for occupational groups such as uranium miners; but the results of case-control studies of indoor radon exposure have documented that residential exposure to radon in indoor air is significantly associated with increased lung cancer risk.
The assumptions made by the Environmental Protection Agency and the Biological Effects of Ionizing Radiation VI Committee of the National Research Council have led to estimates that approximately 15,000 to 20,000 lung cancer deaths per year in the United States are caused by radon. In the United States, the Environmental Protection Agency has called for testing of all residences and mitigation when guideline values are exceeded.
Environmental Factors
Paul T. Strickland, Thomas W. Kensler, in Abeloff's Clinical Oncology (Fifth Edition), 2014
Radon
Radon gas is encountered in hard rock mining for iron, tin, fluorspar, and uranium. The radioactive decay of radon and its products produces alpha particles. The earliest reports defining an association between lung cancer and mining described the high rate of lung cancers among uranium miners in the Schneeberg region of Czechoslovakia in the late 19th century. Many potential causes were proposed, including radon inhalation. Studies of lung cancer mortality among Colorado uranium miners demonstrated dose-related increases in lung cancer risk in miners with protracted exposure to radon.1 In addition, small cell undifferentiated carcinomas predominated in miners with high exposure to radon, in contrast to the typical distribution of pulmonary cancer pathology in the general U.S. population. An elevated risk of lung cancer also has been reported for iron ore miners in England, France, and Sweden; however, the proportion of risk attributable to radon in these populations is more difficult to assess.
Analysis of lung cancer mortality and smoking in Colorado uranium miners suggests a greater than additive mortality rate for cumulative radon exposure and cumulative cigarette smoking.7 In other words, the increased risk of lung cancer among miners compared with nonminers is larger when comparing smokers than when comparing nonsmokers. Interestingly, among atomic bomb survivors, cigarette smoking and radiation exposure only have an additive effect for lung cancer risk. This anomaly has been attributed to the different exposure patterns experienced by atomic bomb survivors (acute) and uranium miners (protracted).
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DNA and Cancer
Dr.Eugene Rosenberg, in It's in Your DNA, 2017
The element radon is responsible for the majority of the natural exposure of the public to cancer-inducing radiation. It is often the single largest contributor to an individual’s background radiation dose. Radon is a chemical element with symbol Rn and atomic number 86. It is a radioactive, colorless, odorless, tasteless, gas, occurring naturally as a decay product of uranium. Since uranium is essentially ubiquitous in the earth’s crust, radon is present in almost all rocks, soils, and water. However, the concentration of radon is variable from location to location. Radon gas from natural sources can accumulate in buildings, especially in confined areas, such as attics, and basements. It can also be found in some spring waters and hot springs.
Radiation Therapy
Alain P. Théon, in Diagnosis and Management of Lameness in the Horse (Second Edition), 2011
Interstitial Brachytherapy
Radon gas (222Rn) in beads and radioactive gold (198Au) pellets that emit γ-rays have been used for interstitial brachytherapy. Radioactive sources are inserted permanently and slowly deliver the radiation dose to the surrounding tissue, until complete decay occurs. To minimize personnel exposure, the implantation procedure is done in two steps: first, the insertion of unloaded needles in tissues according to specific radiation planning rules; and second, the loading of the needles with radioactive sources using a special implantation instrument. Achieving consistently satisfactory implants requires a good deal of practice. Treatment is expensive, because radioactive sources can be used only once. This technique is now used rarely and is not allowed in most areas of the United States (the reader may inquire at the local department of social and health services for state regulations, or with the appropriate government agency in other countries). The major drawback is the potential radiation hazard, because the implant is still radioactive when the horse is discharged from the hospital.
Lung Cancer
Steven E. Weinberger MD, MACP, FRCP, ... Jess Mandel MD, FACP, in Principles of Pulmonary Medicine (Seventh Edition), 2019
Miscellaneous Factors
Exposure to radon, a gas that is a decay product of radium-226 (itself a decay product of uranium-238), is a clear risk factor for the development of lung cancer. Epidemiologic studies of uranium miners exposed to high levels of radon working in the United States and Europe prior to the 1980s, when the risk was identified, demonstrated an increased incidence of both small cell and squamous cell carcinoma (see discussion of pathology further on). The risk appears to be mitigated by improved working conditions in mines.
Exposure to much lower levels of this known carcinogen may occur indoors in homes built on soil that has a high radium content and is releasing radon into the surrounding environment. The finding of unacceptably high levels of radon in some home environments has sparked concern about the risk of lung cancer and interest in widespread testing of houses. Household levels of radon never come close to the level experienced by miners, so some uncertainty remains about the overall risk posed by exposure to household radon. However, most authorities agree there is a small but real increased risk of lung cancer associated with elevated home levels. It has been suggested that radon is the second most important factor contributing to lung cancer and is potentially responsible for 20,000 lung cancer deaths per year in the United States.
Some evidence suggests that dietary factors may affect the risk of lung cancer. Some studies have reported an association between low intake and serum levels of beta carotene, the provitamin form of vitamin A, with an increased risk of lung cancer. However, the data relating to this issue are controversial. An increased risk associated with low dietary intake of beta carotene, if it exists, is relatively minor compared with the risk posed by cigarette smoking. Three large randomized trials have failed to demonstrate a protective effect of beta carotene, alpha tocopherol, or retinoid supplementation on lung cancer risk. The issue is further complicated by data suggesting an increase in the incidence of lung cancer in some trials of individuals given supplements.
Human immunodeficiency virus (HIV) infection increases the risk of lung cancer; this association has become more important as advances in antiretroviral treatment decrease mortality from infectious causes in this population. Patients who have received radiation therapy to the thorax (e.g., as treatment for breast cancer or Hodgkin lymphoma) are at increased risk for lung cancer. Finally, in developing countries, chronic exposure to wood smoke is believed to be responsible for a sizable fraction of lung cancers, particularly among women.
Epidemiology of Lung Cancer
Anthony J. Alberg PhD, MPH, ... Jonathan M. Samet MD, MS, in Murray and Nadel's Textbook of Respiratory Medicine (Sixth Edition), 2016
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