Radiation protection in humans: extending the concept of as low as reasonably achievable (ALARA) from dose to biological damage.

Radiation protection in humans: extending the concept of as low as reasonably achievable (ALARA) from dose to biological damage Ionizing radiation has proven to be a double-edged sword since its discovery by Dr Roentgen in 1895. Radiation is a potent mutagen and carcinogen; however, it is also used in the diagnosis and treatment of human diseases. Background radiation consists of cosmic radiation and radiation emitted from radioactive substances present in the ground or commercial sources. Thus, all living organisms have been exposed to background radiation since their appearance on Earth. The appearance of oxygen some 4.5 billion years ago, allowed the appearance of aerobic organisms that used oxygen for their survival. The usage of oxygen generated toxic chemical species, free radicals, as byproducts. The interaction of radiation with oxygen may have caused increased production of free radicals. In order to cope with these adverse conditions, aerobic organisms that survived have antioxidant defence systems to quench excessive levels of free radicals and repair systems that can correct mutagenic changes. Today, humans, well equipped with antioxidant systems (from dietary and endogenous sources) and efficient repair mechanisms, are constantly exposed to varying levels of background radiation, depending upon the region and altitude where they live. In the USA, the average annual effective dose equivalent from natural sources to a member in the population is about 3.0 mSv (2.0 mSv from radon and 1 mSv from cosmic, terrestrial and internal) [1]. Medical exposure, consumer products, occupational, fallout , nuclear fuel cycle and miscellaneous contribute to about 0.6 mSv [1]. Patients can receive medical radiation exposure of varying levels up to 100 mSv, generally about 20 mSv or less, for diagnostic purposes. The use of radiation in medicine has always been rationalized on the basis of risk vs benefit. Owing to the growing use of nuclear energy in the world, especially in developed countries for civilian and military purposes, the concept of risk was applied to all personnel involved with radiation. In order to further safeguard against potential radiation damage, the concept of maximum permissible dose (MPD) was developed for the two major population groups. The annual MPD value for the general population for stochastic-effects, where the probability of the biological effect is proportional to the dose (linear no-threshold effect) is about 50 times less (1 mSv) than that recommended for radiation workers (50 mSv). In the UK, the radiation worker standard is 20 mSv …