Radiation Protection Today - Winter 2022 Issue 4 | Page 32


The Linear Non-Threshold dose-response model for cancer will remain central to radiological protection practice
John Harrison was formerly Director of the Centre for Radiation , Chemical and Environmental Hazards at Public Health England ( now part of the UK Health Security Agency ) and a member of the International Commission on Radiological Protection ( ICRP ) Main Commission . He currently chairs the UK Department of Health and Social Care ( DHSC ) Committee on Medical Aspects of Radiation in the Environment ( COMARE ).
Simon Bouffler is Deputy Director in the Radiation , Chemical and Environmental Hazards Directorate of UKHSA , a member of the ICRP Main Commission , and UK Representative to the United Nations Scientific Committee on the Effects of An intuitive way of demonstrating the effectiveness Atomic Radiation ( UNSCEAR ). of shielding and radiation doses to operators is through dose rate contours Richard Wakeford is Honorary Professor in Epidemiology at The University of Manchester , Editor-in-Chief of the Journal of Radiological Protection for many years , a member of ICRP Committee 1 and a member of the UK delegation to UNSCEAR .
Optimisation and problems with ALARA The central radiological protection principle of the optimisation of protection from ionising radiation is that doses are kept As Low As Reasonably Achievable ( ALARA ). In fact , the full definition of optimisation given by the International Commission on Radiation Protection is that the likelihood of incurring exposures , the number of people exposed , and the magnitude of their individual doses should all be kept as low as reasonably achievable , taking into account economic and social factors .
There are widespread concerns among Radiation Protection ( RP ) professionals that ALARA is being interpreted over-zealously as dose minimisation , without due consideration of the costs involved and benefits accrued . Such difficulties have led many individuals to espouse beliefs and select evidence that low doses of radiation are not at all harmful , and even that they may be beneficial . Superficially tempting though this approach may be , it is not the answer . There is strong and growing scientific evidence in support of the use of a LNT doseresponse model for cancer at low doses or low dose-rates , and we conclude that this is a realistic rather than overly conservative assumption for RP purposes .
ICRP application of science The system of protection recommended by the ICRP , and used worldwide , is predicated on the prevention of tissue reactions occurring above thresholds of dose ( e . g . skin burns , bone marrow failure ) and the optimisation of protection against stochastic effects , principally cancers . For stochastic effects , it is assumed that the probability of occurrence increases with increasing dose with no threshold below which there is no risk of harm . Based largely on epidemiological data for cancer rates in the Japanese survivors of the atomic bombings at Hiroshima and Nagasaki , ICRP ’ s most recent analyses resulted in severity-adjusted risk coefficients of 5.5 % per sievert ( Sv ) for cancer in the whole population and 4.1 % per Sv for the working-age population . Making small additions for heritable effects , total values were 5.7 % per Sv and 4.2 % per Sv , respectively , noting that there is little direct evidence of heritable effects of radiation in humans . The ICRP notes that this approximates to a fatal risk coefficient of about 5 % per Sv .
Epidemiological evidence Conclusions regarding dose-response models for cancer require consideration of all
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