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Flight attendants and pilots are at the highest risk of dying from radiation-related cancers even more than people who work with radioactive materials, according to a new study. Cosmic radiation comes from space. Only a small amount reaches the Earth’s surface, but exposure is greater for people flying at high altitudes. There’s been limited evidence from small studies suggesting that the exposure translates to higher cancer death rates among people who fly often particularly pilots and flight attendants………Continue reading….
Source: CNN
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Critics:
Exposure to ionizing radiation is known to increase the future incidence of cancer, particularly leukemia. The mechanism by which this occurs is well understood, but quantitative models predicting the level of risk remain controversial. The most widely accepted model posits that the incidence of cancers due to ionizing radiation increases linearly with effective radiation dose at a rate of 5.5% per sievert; if correct, natural background radiation is the most hazardous source of radiation to general public health, followed by medical imaging as a close second.
Additionally, the vast majority of non-invasive cancers are non-melanoma skin cancers caused by ultraviolet radiation (which lies on the boundary between ionizing and non-ionizing radiation). Non-ionizing radio frequency radiation from mobile phones, electric power transmission, and other similar sources have been investigated as a possible carcinogen by the WHO’s International Agency for Research on Cancer, but to date, no evidence of this has been observed.
According to the prevalent model, any radiation exposure can increase the risk of cancer. Typical contributors to such risk include natural background radiation, medical procedures, occupational exposures, nuclear accidents, and many others. Some major contributors are discussed below. Radon is responsible for the worldwide majority of the mean public exposure to ionizing radiation. It is often the single largest contributor to an individual’s background radiation dose, and is the most 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. Epidemiological evidence shows a clear link between lung cancer and high concentrations of radon, with 21,000 radon-induced U.S. lung cancer deaths per year—second only to cigarette smoking—according to the United States Environmental Protection Agency.
Thus in geographic areas where radon is present in heightened concentrations, radon is considered a significant indoor air contaminant. Residential exposure to radon gas has similar cancer risks as passive smoking. Radiation is a more potent source of cancer when it is combined with other cancer-causing agents, such as radon gas exposure plus smoking tobacco. In industrialized countries, medical imaging contributes almost as much radiation dose to the public as natural background radiation.
Collective dose to Americans from medical imaging grew by a factor of six from 1990 to 2006, mostly due to growing use of 3D scans that impart much more dose per procedure than traditional radiographs. CT scans alone, which account for half the medical imaging dose to the public, are estimated to be responsible for 0.4% of current cancers in the United States, and this may increase to as high as 1.5–2% with 2007 rates of CT usage; however, this estimate is disputed.
Other nuclear medicine techniques involve the injection of radioactive pharmaceuticals directly into the bloodstream, and radiotherapy treatments deliberately deliver lethal doses (on a cellular level) to tumors and surrounding tissues. It has been estimated that CT scans performed in the US in 2007 alone will result in 29,000 new cancer cases in future years. This estimate is criticized by the American College of Radiology (ACR), which maintains that the life expectancy of CT scanned patients is not that of the general population and that the model of calculating cancer is based on total-body radiation exposure and thus faulty.
In accordance with ICRP recommendations, most regulators permit nuclear energy workers to receive up to 20 times more radiation dose than is permitted for the general public. Higher doses are usually permitted when responding to an emergency. The majority of workers are routinely kept well within regulatory limits, while a few essential technicians will routinely approach their maximum each year. Accidental overexposures beyond regulatory limits happen globally several times a year.
Astronauts on long missions are at higher risk of cancer, see cancer and spaceflight. Some occupations are exposed to radiation without being classed as nuclear energy workers. Airline crews receive occupational exposures from cosmic radiation because of reduced atmospheric shielding at altitude. Mine workers receive occupational exposures to radon, especially in uranium mines. Anyone working in a granite building, such as the US Capitol, is likely to receive a dose from natural uranium in the granite.
Cancer is a stochastic effect of radiation, meaning it is an unpredictable event. The probability of occurrence increases with effective radiation dose, but the severity of the cancer is independent of dose. The speed at which cancer advances, the prognosis, the degree of pain, and every other feature of the disease are not functions of the radiation dose to which the person is exposed.
This contrasts with the deterministic effects of acute radiation syndrome which increase in severity with dose above a threshold. Cancer starts with a single cell whose operation is disrupted. Normal cell operation is controlled by the chemical structure of DNA molecules, also called chromosomes. When radiation deposits enough energy in organic tissue to cause ionization, this tends to break molecular bonds, and thus alter the molecular structure of the irradiated molecules.
Less energetic radiation, such as visible light, only causes excitation, not ionization, which is usually dissipated as heat with relatively little chemical damage. Ultraviolet light is usually categorized as non-ionizing, but it is actually in an intermediate range that produces some ionization and chemical damage. Hence the carcinogenic mechanism of ultraviolet radiation is similar to that of ionizing radiation.
Unlike chemical or physical triggers for cancer, penetrating radiation hits molecules within cells randomly. Molecules broken by radiation can become highly reactive free radicals that cause further chemical damage. Some of this direct and indirect damage will eventually impact chromosomes and epigenetic factors that control the expression of genes. Cellular mechanisms will repair some of this damage, but some repairs will be incorrect and some chromosome abnormalities will turn out to be irreversible.
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