Journal of radiological protection : official journal of the Society for Radiological Protection
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Current technical radiotherapy advances aim to (a) better conform the dose contours to cancers and (b) reduce the integral dose exposure and thereby minimise unnecessary dose exposure to normal tissues unaffected by the cancer. Various types of conformal and intensity modulated radiotherapy (IMRT) using x-rays can achieve (a) while charged particle therapy (CPT)-using proton and ion beams-can achieve both (a) and (b), but at greater financial cost. Not only is the long term risk of radiation related normal tissue complications important, but so is the risk of carcinogenesis. ⋯ In principle, this new approach might influence the conduct of proton and ion beam therapy, particularly beam placements and fractionation policies. The theoretical implications for future radiotherapy are considerable, but these predictions should be subjected to cellular and tissue experiments that simulate these forms of treatment, including any secondary neutron production in some cases depending on the beam delivery technique, e.g. in tissue equivalent humanoid phantoms using cell transformation techniques. Since the UK has no working high energy particle beam facility over 100 MeV, British scientists would require use of particle beam facilities in Europe, USA or Japan to perform experiments.
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The survivors of the atomic bombings in Hiroshima and Nagasaki are a general population of all ages and sexes and, because of the wide and well characterised range of doses received, have been used by many scientific committees (International Commission on Radiological Protection (ICRP), United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR), Biological Effects of Ionizing Radiations (BEIR)) as the basis of population cancer risk estimates following radiation exposure. Leukaemia was the first cancer to be associated with atomic bomb radiation exposure, with preliminary indications of an excess among the survivors within the first five years after the bombings. An excess of solid cancers became apparent approximately ten years after radiation exposure. ⋯ Although cardiovascular risks have been seen elsewhere, particularly in medically exposed groups, in contrast with the cancer data there is much less consistency in risk between studies: risks per unit dose in epidemiological studies vary over at least two orders of magnitude, possibly as a result of confounding factors. In the absence of a convincing mechanistic explanation of epidemiological evidence, at present a cause-and-effect interpretation of the reported statistical associations for cardiovascular disease is unreliable but cannot be excluded. Further epidemiological and biological evidence will allow a firmer conclusion to be drawn.
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Many individuals are, or have been, exposed to ionising radiation in the course of their work and the epidemiological study of occupationally irradiated groups offers an important opportunity to complement the estimates of risks to health resulting from exposure to radiation that are obtained from other populations, such as the Japanese survivors of the atomic bombings of Hiroshima and Nagasaki in 1945. Moreover, workplace exposure to radiation usually involves irradiation conditions that are of direct relevance to the principal concern of radiological protection: protracted exposure to low level radiation. Further, some workers have been exposed to radioactive material that has been inadvertently taken into the body, and the study of these groups leads to risk estimates derived directly from the experience of those irradiated by these 'internal emitters', intakes of alpha-particle-emitters being of particular interest. ⋯ Early workers from the Mayak plutonium production facility in Russia were heavily exposed to external sources of penetrating radiation and to plutonium, and appreciable effort has been expended in obtaining dependable risk estimates from this scientifically valuable group of workers. Those occupationally exposed to low levels of radiation also present an opportunity of studying possible somatic health effects other than cancer, such as heart disease and eye cataracts, that are the subject of much discussion at present. Overall, studies of exposure to ionising radiation in the workplace provide a valuable support to studies of those groups exposed under other circumstances, and in some instances (such as exposure to plutonium) effectively offer the only direct source of epidemiological evidence on risks.