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

摘要: Ionizing radiation has proven to be a double-edged sword since its discovery by Dr Roentgen in 1895. Radiation is potent mutagen and carcinogen; however, it also used the diagnosis treatment of human diseases. Background consists cosmic emitted from radioactive substances present ground or commercial sources. Thus, all living organisms have been exposed background their appearance on Earth. The oxygen some 4.5 billion years ago, allowed aerobic that for survival. usage generated toxic chemical species, free radicals, as byproducts. interaction with may caused increased production radicals. In order cope these adverse conditions, survived antioxidant defence systems quench excessive levels radicals repair can correct mutagenic changes. Today, humans, well equipped (from dietary endogenous sources) efficient mechanisms, are constantly varying radiation, depending upon region altitude where they live. USA, average annual effective dose equivalent natural sources member population about 3.0 mSv (2.0 radon 1 cosmic, terrestrial internal) [1]. Medical exposure, consumer products, occupational, fallout, nuclear fuel cycle miscellaneous contribute 0.6 Patients receive medical exposure up 100 mSv, generally 20 less, diagnostic purposes. use medicine always rationalized basis risk vs benefit. Owing growing energy world, especially developed countries civilian military purposes, concept was applied personnel involved radiation. further safeguard against potential damage, maximum permissible (MPD) two major groups. MPD value general stochasticeffects, probability biological effect proportional (linear no-threshold effect) 50 times less (1 mSv) than recommended workers (50 mSv). UK, worker standard [2]. Although above remained fairly constant during last several decades, this US reduced factor 5 1991 [3] made law 1993. This due emergence new data low doses somatic heritable mutations mammals mammalian cells culture [4–7], synergistic other carcinogens tumour promoters cancer incidence mutations, epidemiological studies humans. To address concerns radiation-induced ALARA (as reasonably achievable) respect national international protection agencies [2, 3]. Efforts protect normal tissues were started soon after X-rays. However, observation Muller Columbia University 1927, causes gene inDrosophila melanogaster (common fruit fly) provided impetus reduce exposures [5]. initial three physical principles: (a) shielding (usually lead) unexposed areas, radiosensitive organs such bone marrow, gonads thyroid; (b) distance between source patients; (c) reduction time. Each factors very useful, but limitations. For example, fluoroscopy, not possible gastrointestinal tract (one most organs) damage lead shielding. Increasing individuals practical many workers, patients, personnel. Reducing time pertinent populations, except those taking care patients who received gammaemitting radioisotopes purposes responsible decontamination result accidents attack. Nevertheless, based served useful purpose successful reducing level unnecessary workers. Received 31 March 2003 final form September 2003, accepted 22 2003. British Journal Radiology, 77 (2004), 97–99 E 2004 Institute Radiology DOI: 10.1259/bjr/88081058