DOES RADIATION CAUSE CANCER? IT DEPENDS ON THE dose. What dose? There's no question that ionizing radiation at high doses can cause cancer, but there are no data to support this connection at low doses. We are literally bathed every second of every day in such low-dose radiation due to natural background radiation, exposures that vary annually from a few mGy (mGy is milligray, a unit of ionizing radiation dose in the International System of Units). There is an average exposure of 3 mGy in the U.S. to 260 mGy on the rest of the planet depending upon where one lives. For comparison, a computed tomography (CT) medical imaging scan is about 10 mGy. Irrespective of the level of background or other low-dose exposure to a given population, no associated health effects have been documented to date anywhere in the world. Nevertheless, for more than 50 years, the linear no-threshold hypothesis (LNTH) has been a tenet of industrial, radiological, and medical scientific thought and practice. (1) This hypothesis is used for cancer risk estimation from exposure to ionizing radiation all the way down to zero dose.
The LNTH is based on observed effects at high radiation doses, with unobserved, low-dose effects being extrapolated by modeling linearly downward, meaning that the proven consequence of high doses has simply been assumed to apply even near zero dose, with no threshold below which radiation is harmless. Hence it predicts some level of cancer at all doses.
The problem with this hypothesis is that the body responds differently to radiation at high v. low doses, as proven in many studies: high-dose responses are associated with extensive damage while at low doses the body eliminates the damage through a variety of protective mechanisms, evolved in humans from eons of living in a world bathed in slowly delivered but sometimes high-dose natural radiation. Importantly, low dose radiation-induced carcinogenesis has never been demonstrated by empirical evidence. Yet, the LNTH has resulted in the development, implementation, and application of global regulations, policies and recommendations from government regulators and industry advisory bodies for rigorous control of both actual and potential exposures to low-dose ionizing radiation (LDIR) generated by selected industries and practices for both workers and the general public. Dropping atomic bombs over the Japanese cities of Hiroshima and Nagasaki allowed for the testing of the LNTH with respect to carcinogenic mortality of human beings from radiation exposure, including LDIR. Such research was undertaken shortly after the war with the formation of the Atomic Bomb Casualty Commission, soon succeeded by the Radiation Effects Research Foundation (RERF) in Japan (http://www.rerf.jp), in cooperation with the United States. The RERF's Life Span Study (LSS) is used to promote the LNTH for dose-response data involving acute dosages received by populations proximate to weapon detonation and age/sex-adjusted cancer mortality of these populations. The LSS cohort of A-bomb survivors is the single most important data base--the "gold standard"--for estimating radiation effects in humans. (2)
Based mainly on LSS data, a committee of the National Academy...
This is a preview. Get the full text through your school or public library.