1990, The British Journal of Radiology, 63, 373-376 Proceedings of the British Institute of Radiology
Radiation protection: sense or nonsense? Abstracts of papers presented at an all-day meeting of the BIR held at the Windeyer Building, Middlesex Hospital, Cleveland Street, London W1 on Wednesday, 13 December 1989 Chairman: Dr R. J. Berry Cancer in Swedish iron miners; a nearly complete follow-up study, by E. Radford Radon exposure, marrow and fetal dose, and leukaemia, by D. L. Henshaw Incidence of leukaemia in young people in the vicinity of Hinkley Point nuclear power station, by P. Ewings, C. Bowie, M. J. Phillips and S. A. N. Johnson Occupational exposure and the central index of dose information, by G. M. Kendall Medical diagnostic exposure, by J. G. B. Russell Medical therapeutic exposure, by M. J. Day The standard man in diagnostic radiology dosimetry, by B. A. Lindskoug Reduction of dose due to radon in housing, by S. J. Wozniak Reduction of occupational dose, by R. J. Berry Reduction of dose in diagnosis, by B. F. Wall Radiation protection—the environmental view, by P. Green
Cancer in Swedish iron miners; a nearly complete follow-up study Edward P. Radford Woking, Surrey We have obtained mortality data for 1415 Swedish iron miners who worked underground and were exposed to relatively low concentrations of radon daughters. The cohorts studied were men born between 1880 and 1919 who were alive on January 1st 1930. Control populations have been the Swedish national population and men from the nearby communities from the same birth years. Follow-up has now been completed up to 1986, at which time only 30% of the miners were still alive. Thus this study population is epidemiologically the most complete in the world of any group studied prospectively. Comparison of the two control populations shows that causes of death differed significantly for the local population compared to Swedish national rates. For example, a stomach cancer excess among miners is found to be present among local controls as well. Seventy-three deaths from lung cancer have been observed among miners compared with 17.6 expected from community data. The absolute excess lung cancer risk for cigarette smokers is 1.66 times that for non-smokers, but the relative risk coefficient for non-smokers is four times that for smokers. The excess relative risk for lung cancer has continued unchanged even though all men have retired from underground work since 1978. A significant excess of multiple myeloma has been observed among the miners in recent follow-up years, and a more than three-fold excess of liver and gall bladder cancers has also been found. The evidence suggests that these last two observations may be related to occupational radon exposure.
Radon exposure, marrow and fetal dose, and leukaemia D. L. Henshaw H. H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol BS8 1TL Recent calculations of dose from inhaled radon to bone marrow and the fetus yield values considerably higher than that assumed by ICRP. By taking into account the presence of fat in marrow, in which radon is 16 times more soluble than in blood, and the contribution from inhaled excess radon daughters in room air, we calculate, for a radon exposure of Vol. 63, No. 749
20 Bq/m3, marrow doses of 123 /xSv/y and 129/xSv/y4 for the adult and a child aged 10, respectively. For the fetus the doses are in the range 28-49 /xSv/y. For radon exposures of 400 Bq/m3, the respective doses are 2600, 2620 and 540-1120 /iSv/y. These results suggest that domestic radon exposure could be a causative factor in the induction of leukaemia. We have therefore looked for an association between radon exposure and leukaemia incidence in particular but of other cancers in general. International incidence of myeloid leukaemia, cancer of the kidney, melanoma and certain childhood cancers all show significant correlation with radon exposure in the home. For myeloid leukaemia analysis suggests that overall in the UK between 5% and 10% of incidence may be attributed to radon. In Cornwall, where radon levels are higher, we estimate that at least 17% of myeloid leukaemia is caused by radon.
Incidence of leukaemia in young people in the vicinity of Hinkley Point nuclear power station P. Ewings, C. Bowie, *M. J. Phillips and *S. A. N. Johnson Somerset Health Authority, Taunton and *Musgrove Park Hospital, Taunton, Somerset Data reported in Ewings et al (1989) are discussed. Cancer registry data are used to examine the incidence of leukaemia and lymphoma in persons aged under 25 years living in the vicinity of Hinkley Point nuclear power station. The 19 cases occurring in a predefined area around Hinkley Point during 1964-1986 are 82% more than expected from national rates (95% confidence interval 10% to 185%). However, Somerset as a whole has high rates compared to the national average, and the area around Hinkley Point has only 54% more cases than the Somerset average. This figure is not statistically significantly higher, so the high rate around Hinkley Point may simply be reflecting the generally high rate in the Somerset area. Temporal patterns are examined using standard 5 year intervals. Particularly high rates are revealed around Hinkley Point for the 10 years following commissioning of the station (1964-1973), when rates in the rest of Somerset were similar to the national average. In particular, the nine cases occurring in the 5 year period 1969-1973 is about four times the number
373
Proceedings of the British Institute of Radiology expected from national rates. After 1973, the rates around Hinkley Point are fairly low. The pattern of leukaemia cases observed around Hinkley Point cannot readily be explained. In common with results for other nuclear installations, radioactive emissions do not provide a plausible explanation according to current understanding of exposure, dose/risk relationships, etc. The possibility that the current models are flawed is examined. Other possibilities recently suggested, namely the implication of viral transmission resulting from the influx of a large workforce into a susceptible community, and geographical factors common to installation sites, are discussed.
Radiation protection: sense or nonsense medical diagnostic exposure J. G. B. Russell Department of Radiology, St Mary's Hospital, Manchester M13 OJH In the United Kingdom the average population radiation dose for the average diagnostic room is 4 man Sv. This varies from room to room. A busy room devoted mainly to chest work would give only about 1 man Sv per year; a busy barium room is likely to give 10 man Sv per year or more. The new risk factors for a population with the age distribution of patients is Reference likely to indicate a risk of fatal cancer induction at a rate of 3% EWINGS, P. D., BOWIE, C, PHILLIPS, M. J. & JOHNSON, per Sv. Adding the risk of non-fatal cancer and genetic injury S. A. N., 1989. Incidence of leukaemia in young people in the will give a risk of serious radiogenic injury at a rate of 4% per vicinity of Hinkley Point nuclear power station, 1959-86. Sv. With an annual United Kingdom population dose from British Medical Journal, 299, 289-293. diagnostic radiography of 16 000 man Sv per year this indicates about 640 serious radiogenic injuries will occur each year, most of them fatal cancers from diagnostic radiography. Using the new risk factors and using established methods of assessing the value of harm a reasonablefigureto spend to avert 1 man Sv is £20000. The cost of saving radiation in a diagnostic department is trivial compared to this value. Many of the methods which will be discussed by Mr Wall cost nothing. For Occupational exposure and the Central Index of Dose instance, the careful use of the lead shutters, the avoidance in Information an examination of views which add no information and not G. M. Kendall doing unnecessary examinations are obvious examples in this category. The cost of other methods of saving radiation, e.g. National Radiological Protection Board, Chilton, Didcot, Oxon using rare earth screens or low attenuation components in the 0X11 ORQ Optimized control of the radiation exposure of workers apparatus which lie in the primary beam, are also highly cost requires a knowledge of the individual's full radiation dose effective. history. There are obvious difficulties in assembling comprehensive dose histories for workers who change employment and a number of countries have set up dose depositories to make this process more reliable. The UK scheme is known as the Central Index of Dose Information (CIDI). It is operated Medical therapeutic exposure on behalf of the Health and Safety Executive by the National M. J. Day Radiological Protection Board. In order to keep costs to a Newcastle minimum CIDI operates by exchanging data with Approved Radiotherapeutic exposure is unique in that the object is to Dosimetry Services in the form of closely defined computer bring about a definite and beneficial radiobiological effect. compatible records. While the use of computerized data Consequently the general principles of radiation protection are transfer makes for more economical running it is potentially only marginally applicable and it is difficult to make dangerous since the data are not scanned by human meaningful comparisons with other types of exposure. The intelligence. Special data vetting software has been written for local tumour dose is relatively high (e.g. 50 Gy) and the quality assurance. Special attention is given to ensuring that whole-body average dose is typically a few gray. About 1 in 10 successive employments of an individual are brought together of the population receive radiotherapy. Patients are usually even if the name or National Insurance number may have been elderly and have reduced life-expectancy and fertility. The mis-reported. Occupational exposure to ionizing radiation in contribution to the GSD is only marginal. Although radiothe UK is covered by the 1985 Ionizing Radiations Regula- therapeutic exposure must be justified by the expectation of net tions. About 40000 individuals are radiation workers within benefit to the patient, the system of dose limitation and the the sense of these regulations. It is this group which will be concept of acceptable risk are not applicable. The dosage to covered by the CIDI. However, personal monitoring is not normal tissues should indeed be minimized, but in the absence restricted to these "classified workers" and many more of an alternative to the effective dose equivalent it is difficult to individuals are monitored in order to provide reassurance. apply the ALARA principle. In radiotherapy, optimization When the variation of mean dose to a group of workers with involves balancing cure-rate against the risk of high-dose time is explored it is generally found that there is a downward effects such as necrosis, with virtually no cost implications. The trend, i.e. doses appear to be falling. However, it is often optimal practice of radiotherapy requires reliable dosimetry, difficult to be sure that this does not arise through the good anatomical localization, individual planning and accurate "dilution" of a group of genuine radiation workers by administration of the treatment. By contrast, optimization of individuals receiving low dose. Evidence from one large radiation protection involves off-setting the cost of protective Personal Monitoring Service has now been found to suggest measures against reduction of collective dose: essentially a that this is not the case and that the reduction in mean dose matter for society as a whole. The risk estimates used in with time is genuine. There is also interest in the variation in radiation protection have some limited application to the mean dose between different occupational groups. The workers incidence of radiation-induced tumours outside the main receiving the largest doses work in non-coal mines, in 1987 the treatment zone. Methods for protection against occupational mean dose was reported to be 14 mSv, higher by a factor of exposure in external beam radiotherapy and brachytherapy are three than the next largest group. discussed briefly. 374
The British Journal of Radiology, May 1990
Proceedings of the British Institute of Radiology The standard man in diagnostic radiology dosimetry Bengt A. Lindskoug Regional Department of Radiation and Hospital Physics, S-301 85 Halmstad, Sweden One problem with the ICRP standard man is that less than one quarter of the human population on this planet corresponds with the Caucasian dimensions stipulated. Moreover, even the average weight of a limited European population rarely agrees with the expected 70 kg. Infants, children, adolescents or obese adults unbalance the distribution. Similar problems exist in using Monte Carlo tables computed for the standard man, no limited population will agree. The same problem occurs when comparing two samples of patient examinations. The populations equal neither in weight, nor height, nor constitution. This is the major reason for the extreme deviation of absorbed dose given to patients during diagnostic radiology examinations. A close relation is found between the total energy imparted during radiology examinations of the trunk and the equivalent cylindrical diameter (De) of the patient body. Exponential functions are created by linear regression in logarithmic space. Coordinate transformations reduce data to a base-line defined by the ICRP standard man with De = 22.9 cm. Organ dose and effective dose equivalent are computed from the reduced data. By standardizing data in accordance with exponential functions using the equivalent diameter as the independent variable, the deviation is reduced according to the following table:
Examination
Lumbar spine Thoracic spine Urography Colon Chest Heart and lung
Relative reduction ( %) Mean dose
SD
High/low ratio
15 12 28 13 12 12
51 19 62 5 41 39
76 22 94 85 74 90
Improved diagnostic precision and reduced total energy imparted to individuals (film exposure plus radiography), which includes improved image quality and reduced dose, are the parameters that should be optimized for a mutual technical and methodical improvement and assessment of organ dose for future classification of detrimental effects.
Reduction of dose due to radon in housing Stephen J. Wozniak Building Research Establishment, Garston, Watford WD2 7JR The Building Research Establishment is undertaking work in existing housing to determine appropriate remedial options for elevated indoor radon levels. Initial studies have been undertaken in houses identified by NRPB and having the highest concentrations. Most of these are located in Devon and Cornwall. Work in new housing is also in progress to determine appropriate protection or remedial treatments. A feature of domestic radon exposure in the UK is that little of the collective effective dose equivalent occurs in "high level" houses. Thus, the prospects for cost-effective dose avoidance may be limited. The UK position is reviewed, based on NRPB estimates of the number of houses having annual average
Vol. 63, No. 749
radon gas concentrations above both 400 Bq/m3 and 200 Bq/m3, the latter being the lower of the two "action levels" suggested for the UK, and close to the USA threshold of 150 Bq/m3. It is shown that, whilst the prospects for technical remediation are good, the realistic potential for premature death avoidance in houses above either action level is certainly less than 100 persons per year, and probably less than 40 per year, including 10 non-smokers. This is compared with an annual total of nearly 40 000 lung cancer deaths, including 2000 calculated to be owing in part to domestic radon exposure and including 500 non-smokers.
Reduction of occupational dose R. J. Berry British Nuclear Fuels pic, Risley, Warrington, Cheshire WA36 AS Over the past decade the requirement to keep doses received occupationally "as low as reasonably achievable", as laid down in ICRP Publication 26 (1977) has effectively halved the average annual dose to workers at British Nuclear Fuels, Sellafield reprocessing plant. Reduction in collective dose has been harder to achieve. In the electricity supply industry, average worker doses have decreased, although less dramatically, both in the UK and in other countries, and the record of the United Kingdom is good in the reduction of both individual and collective occupational dose across the whole of the nuclear industry. Better management of maintenance and refurbishment tasks has achieved significant reductions in worker exposure, but at an economic cost which exceeds the notional value of a man-sievert saved. For reductions in dose to the public from the nuclear industry, the disproportion between the cost and the notional value of a man-sievert saved may be as high as 10 5 : 1. The recommendation by NRPB, that dose limits for occupationally exposed people should be set by averaging over a period up to 10 years, is supported strongly; excessively restrictive annual dose limits do not in practice reduce average occupational exposures and may result in actual increases in collective occupational dose. Examples are given of the way in which the cost of reductions in occupational radiation exposure are managed in BNFL by delegation of financial authority to appropriate levels of management.
Reduction of dose in diagnosis B. F. Wall National Radiological Protection Board, Chilton, Didcot, Oxon The fact that medical X rays contribute about 90% of the total collective dose to the population of the UK from all man-made sources, testifies to the enormous benefit to the health of the nation that is attributed to this use of radiation by both the medical profession and the public. The overall effect of medical X rays is undoubtedly seen as an improvement in health care and to be of benefit, dose reduction in radiodiagnosis must be aimed only at unnecessary medical exposures. It is essentially this unbeneficial component of the collective medical dose that should be more properly compared with other sources of population exposure when assessing the relative urgency of directing resources at reducing them, since no other source of radiation exposure can claim to have the direct health benefit potential of medical radiology. This paper attempts to assess the extent of unnecessary medical exposures in the UK, which turns out to be substantial. Possibly as much as one third of the
375
Proceedings of the British Institute of Radiology collective dose from medical X rays could be avoided without jeopardizing patient care. It goes on to determine the cost and effectiveness of a number of dose reduction methods. Many simple changes in procedure cost nothing while some dose saving improvements in equipment, like changing over to rare-earth screens, are also found to be extremely cost-effective and yet surprisingly have not received anything like universal adoption in the NHS. One reason for the low priority given to radiation protection in the health service may be the competition from other more effective methods of health care for the same limited resources. A rough comparison was made of the cost-effectiveness of some radiation protection options and a range of common medical procedures, in terms of the cost per quality adjusted life year saved (£/QALY). It indicated that even relatively expensive patient protection measures (like carbon fibre table tops) appear to compete favourably with a number of medical procedures that already consume large amounts of health service resources.
Radiation Protection: the environmental view Patrick Green Friends of the Earth, 26-28 Underwood Street, London Nl 7JQ For many years environmental groups have claimed that radiological protection standards underestimated the risk from
376
exposure to ionizing radiation. A claim rejected by the nuclear industry and its regulatory authorities as unsupported by the scientific evidence. For such organizations the emphasis was on the ALARA principle (all doses must be kept as low as reasonably achievable) as the most effective way to reduce exposures, not changes in the dose limits. The latest evidence from the Radiation Effects Research Foundation in Japan has changed this. It is now accepted that risk estimates will rise and dose limits will have to be reduced. The question is when should they be changed and by how much? Following the International Commission on Radiological Protection's (ICRP) 1987 Statement that the new evidence was not sufficient to warrant an immediate change in its dose limits, the UK National Radiological Protection Board (NRPB) stated interim guidance was necessary. They recommended a threefold increase in the risk estimates for radiological protection purposes. Since then, at the Hinkley Point ' C Public Inquiry, they have recommended further increases in these risk estimates. These estimates differ from those suggested by Friends of the Earth only in terms of the Dose Rate Effectiveness Factor used. Next year, the ICRP are finally expected to publish their new recommendations. The ICRP's current system of radiological protection is based around three main features: (1) justification, (2) ALARA and (3) dose limits. This talk discusses this system in light of the increases in risk, and considers, from an environmental perspective, what changes should be made.
The British Journal of Radiology, May 1990
Radiation protection: sense or nonsense? Abstracts of papers presented at an all-day meeting of the BIR held at the Windeyer Building, Middlesex Hospital, Cleveland Street, London W1 on Wednesday, 13 December 1989 Chairman: Dr R. J. Berry Cancer in Swedish iron miners; a nearly complete follow-up study, by E. Radford Radon exposure, marrow and fetal dose, and leukaemia, by D. L. Henshaw Incidence of leukaemia in young people in the vicinity of Hinkley Point nuclear power station, by P. Ewings, C. Bowie, M. J. Phillips and S. A. N. Johnson Occupational exposure and the central index of dose information, by G. M. Kendall Medical diagnostic exposure, by J. G. B. Russell Medical therapeutic exposure, by M. J. Day The standard man in diagnostic radiology dosimetry, by B. A. Lindskoug Reduction of dose due to radon in housing, by S. J. Wozniak Reduction of occupational dose, by R. J. Berry Reduction of dose in diagnosis, by B. F. Wall Radiation protection—the environmental view, by P. Green
Cancer in Swedish iron miners; a nearly complete follow-up study Edward P. Radford Woking, Surrey We have obtained mortality data for 1415 Swedish iron miners who worked underground and were exposed to relatively low concentrations of radon daughters. The cohorts studied were men born between 1880 and 1919 who were alive on January 1st 1930. Control populations have been the Swedish national population and men from the nearby communities from the same birth years. Follow-up has now been completed up to 1986, at which time only 30% of the miners were still alive. Thus this study population is epidemiologically the most complete in the world of any group studied prospectively. Comparison of the two control populations shows that causes of death differed significantly for the local population compared to Swedish national rates. For example, a stomach cancer excess among miners is found to be present among local controls as well. Seventy-three deaths from lung cancer have been observed among miners compared with 17.6 expected from community data. The absolute excess lung cancer risk for cigarette smokers is 1.66 times that for non-smokers, but the relative risk coefficient for non-smokers is four times that for smokers. The excess relative risk for lung cancer has continued unchanged even though all men have retired from underground work since 1978. A significant excess of multiple myeloma has been observed among the miners in recent follow-up years, and a more than three-fold excess of liver and gall bladder cancers has also been found. The evidence suggests that these last two observations may be related to occupational radon exposure.
Radon exposure, marrow and fetal dose, and leukaemia D. L. Henshaw H. H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol BS8 1TL Recent calculations of dose from inhaled radon to bone marrow and the fetus yield values considerably higher than that assumed by ICRP. By taking into account the presence of fat in marrow, in which radon is 16 times more soluble than in blood, and the contribution from inhaled excess radon daughters in room air, we calculate, for a radon exposure of Vol. 63, No. 749
20 Bq/m3, marrow doses of 123 /xSv/y and 129/xSv/y4 for the adult and a child aged 10, respectively. For the fetus the doses are in the range 28-49 /xSv/y. For radon exposures of 400 Bq/m3, the respective doses are 2600, 2620 and 540-1120 /iSv/y. These results suggest that domestic radon exposure could be a causative factor in the induction of leukaemia. We have therefore looked for an association between radon exposure and leukaemia incidence in particular but of other cancers in general. International incidence of myeloid leukaemia, cancer of the kidney, melanoma and certain childhood cancers all show significant correlation with radon exposure in the home. For myeloid leukaemia analysis suggests that overall in the UK between 5% and 10% of incidence may be attributed to radon. In Cornwall, where radon levels are higher, we estimate that at least 17% of myeloid leukaemia is caused by radon.
Incidence of leukaemia in young people in the vicinity of Hinkley Point nuclear power station P. Ewings, C. Bowie, *M. J. Phillips and *S. A. N. Johnson Somerset Health Authority, Taunton and *Musgrove Park Hospital, Taunton, Somerset Data reported in Ewings et al (1989) are discussed. Cancer registry data are used to examine the incidence of leukaemia and lymphoma in persons aged under 25 years living in the vicinity of Hinkley Point nuclear power station. The 19 cases occurring in a predefined area around Hinkley Point during 1964-1986 are 82% more than expected from national rates (95% confidence interval 10% to 185%). However, Somerset as a whole has high rates compared to the national average, and the area around Hinkley Point has only 54% more cases than the Somerset average. This figure is not statistically significantly higher, so the high rate around Hinkley Point may simply be reflecting the generally high rate in the Somerset area. Temporal patterns are examined using standard 5 year intervals. Particularly high rates are revealed around Hinkley Point for the 10 years following commissioning of the station (1964-1973), when rates in the rest of Somerset were similar to the national average. In particular, the nine cases occurring in the 5 year period 1969-1973 is about four times the number
373
Proceedings of the British Institute of Radiology expected from national rates. After 1973, the rates around Hinkley Point are fairly low. The pattern of leukaemia cases observed around Hinkley Point cannot readily be explained. In common with results for other nuclear installations, radioactive emissions do not provide a plausible explanation according to current understanding of exposure, dose/risk relationships, etc. The possibility that the current models are flawed is examined. Other possibilities recently suggested, namely the implication of viral transmission resulting from the influx of a large workforce into a susceptible community, and geographical factors common to installation sites, are discussed.
Radiation protection: sense or nonsense medical diagnostic exposure J. G. B. Russell Department of Radiology, St Mary's Hospital, Manchester M13 OJH In the United Kingdom the average population radiation dose for the average diagnostic room is 4 man Sv. This varies from room to room. A busy room devoted mainly to chest work would give only about 1 man Sv per year; a busy barium room is likely to give 10 man Sv per year or more. The new risk factors for a population with the age distribution of patients is Reference likely to indicate a risk of fatal cancer induction at a rate of 3% EWINGS, P. D., BOWIE, C, PHILLIPS, M. J. & JOHNSON, per Sv. Adding the risk of non-fatal cancer and genetic injury S. A. N., 1989. Incidence of leukaemia in young people in the will give a risk of serious radiogenic injury at a rate of 4% per vicinity of Hinkley Point nuclear power station, 1959-86. Sv. With an annual United Kingdom population dose from British Medical Journal, 299, 289-293. diagnostic radiography of 16 000 man Sv per year this indicates about 640 serious radiogenic injuries will occur each year, most of them fatal cancers from diagnostic radiography. Using the new risk factors and using established methods of assessing the value of harm a reasonablefigureto spend to avert 1 man Sv is £20000. The cost of saving radiation in a diagnostic department is trivial compared to this value. Many of the methods which will be discussed by Mr Wall cost nothing. For Occupational exposure and the Central Index of Dose instance, the careful use of the lead shutters, the avoidance in Information an examination of views which add no information and not G. M. Kendall doing unnecessary examinations are obvious examples in this category. The cost of other methods of saving radiation, e.g. National Radiological Protection Board, Chilton, Didcot, Oxon using rare earth screens or low attenuation components in the 0X11 ORQ Optimized control of the radiation exposure of workers apparatus which lie in the primary beam, are also highly cost requires a knowledge of the individual's full radiation dose effective. history. There are obvious difficulties in assembling comprehensive dose histories for workers who change employment and a number of countries have set up dose depositories to make this process more reliable. The UK scheme is known as the Central Index of Dose Information (CIDI). It is operated Medical therapeutic exposure on behalf of the Health and Safety Executive by the National M. J. Day Radiological Protection Board. In order to keep costs to a Newcastle minimum CIDI operates by exchanging data with Approved Radiotherapeutic exposure is unique in that the object is to Dosimetry Services in the form of closely defined computer bring about a definite and beneficial radiobiological effect. compatible records. While the use of computerized data Consequently the general principles of radiation protection are transfer makes for more economical running it is potentially only marginally applicable and it is difficult to make dangerous since the data are not scanned by human meaningful comparisons with other types of exposure. The intelligence. Special data vetting software has been written for local tumour dose is relatively high (e.g. 50 Gy) and the quality assurance. Special attention is given to ensuring that whole-body average dose is typically a few gray. About 1 in 10 successive employments of an individual are brought together of the population receive radiotherapy. Patients are usually even if the name or National Insurance number may have been elderly and have reduced life-expectancy and fertility. The mis-reported. Occupational exposure to ionizing radiation in contribution to the GSD is only marginal. Although radiothe UK is covered by the 1985 Ionizing Radiations Regula- therapeutic exposure must be justified by the expectation of net tions. About 40000 individuals are radiation workers within benefit to the patient, the system of dose limitation and the the sense of these regulations. It is this group which will be concept of acceptable risk are not applicable. The dosage to covered by the CIDI. However, personal monitoring is not normal tissues should indeed be minimized, but in the absence restricted to these "classified workers" and many more of an alternative to the effective dose equivalent it is difficult to individuals are monitored in order to provide reassurance. apply the ALARA principle. In radiotherapy, optimization When the variation of mean dose to a group of workers with involves balancing cure-rate against the risk of high-dose time is explored it is generally found that there is a downward effects such as necrosis, with virtually no cost implications. The trend, i.e. doses appear to be falling. However, it is often optimal practice of radiotherapy requires reliable dosimetry, difficult to be sure that this does not arise through the good anatomical localization, individual planning and accurate "dilution" of a group of genuine radiation workers by administration of the treatment. By contrast, optimization of individuals receiving low dose. Evidence from one large radiation protection involves off-setting the cost of protective Personal Monitoring Service has now been found to suggest measures against reduction of collective dose: essentially a that this is not the case and that the reduction in mean dose matter for society as a whole. The risk estimates used in with time is genuine. There is also interest in the variation in radiation protection have some limited application to the mean dose between different occupational groups. The workers incidence of radiation-induced tumours outside the main receiving the largest doses work in non-coal mines, in 1987 the treatment zone. Methods for protection against occupational mean dose was reported to be 14 mSv, higher by a factor of exposure in external beam radiotherapy and brachytherapy are three than the next largest group. discussed briefly. 374
The British Journal of Radiology, May 1990
Proceedings of the British Institute of Radiology The standard man in diagnostic radiology dosimetry Bengt A. Lindskoug Regional Department of Radiation and Hospital Physics, S-301 85 Halmstad, Sweden One problem with the ICRP standard man is that less than one quarter of the human population on this planet corresponds with the Caucasian dimensions stipulated. Moreover, even the average weight of a limited European population rarely agrees with the expected 70 kg. Infants, children, adolescents or obese adults unbalance the distribution. Similar problems exist in using Monte Carlo tables computed for the standard man, no limited population will agree. The same problem occurs when comparing two samples of patient examinations. The populations equal neither in weight, nor height, nor constitution. This is the major reason for the extreme deviation of absorbed dose given to patients during diagnostic radiology examinations. A close relation is found between the total energy imparted during radiology examinations of the trunk and the equivalent cylindrical diameter (De) of the patient body. Exponential functions are created by linear regression in logarithmic space. Coordinate transformations reduce data to a base-line defined by the ICRP standard man with De = 22.9 cm. Organ dose and effective dose equivalent are computed from the reduced data. By standardizing data in accordance with exponential functions using the equivalent diameter as the independent variable, the deviation is reduced according to the following table:
Examination
Lumbar spine Thoracic spine Urography Colon Chest Heart and lung
Relative reduction ( %) Mean dose
SD
High/low ratio
15 12 28 13 12 12
51 19 62 5 41 39
76 22 94 85 74 90
Improved diagnostic precision and reduced total energy imparted to individuals (film exposure plus radiography), which includes improved image quality and reduced dose, are the parameters that should be optimized for a mutual technical and methodical improvement and assessment of organ dose for future classification of detrimental effects.
Reduction of dose due to radon in housing Stephen J. Wozniak Building Research Establishment, Garston, Watford WD2 7JR The Building Research Establishment is undertaking work in existing housing to determine appropriate remedial options for elevated indoor radon levels. Initial studies have been undertaken in houses identified by NRPB and having the highest concentrations. Most of these are located in Devon and Cornwall. Work in new housing is also in progress to determine appropriate protection or remedial treatments. A feature of domestic radon exposure in the UK is that little of the collective effective dose equivalent occurs in "high level" houses. Thus, the prospects for cost-effective dose avoidance may be limited. The UK position is reviewed, based on NRPB estimates of the number of houses having annual average
Vol. 63, No. 749
radon gas concentrations above both 400 Bq/m3 and 200 Bq/m3, the latter being the lower of the two "action levels" suggested for the UK, and close to the USA threshold of 150 Bq/m3. It is shown that, whilst the prospects for technical remediation are good, the realistic potential for premature death avoidance in houses above either action level is certainly less than 100 persons per year, and probably less than 40 per year, including 10 non-smokers. This is compared with an annual total of nearly 40 000 lung cancer deaths, including 2000 calculated to be owing in part to domestic radon exposure and including 500 non-smokers.
Reduction of occupational dose R. J. Berry British Nuclear Fuels pic, Risley, Warrington, Cheshire WA36 AS Over the past decade the requirement to keep doses received occupationally "as low as reasonably achievable", as laid down in ICRP Publication 26 (1977) has effectively halved the average annual dose to workers at British Nuclear Fuels, Sellafield reprocessing plant. Reduction in collective dose has been harder to achieve. In the electricity supply industry, average worker doses have decreased, although less dramatically, both in the UK and in other countries, and the record of the United Kingdom is good in the reduction of both individual and collective occupational dose across the whole of the nuclear industry. Better management of maintenance and refurbishment tasks has achieved significant reductions in worker exposure, but at an economic cost which exceeds the notional value of a man-sievert saved. For reductions in dose to the public from the nuclear industry, the disproportion between the cost and the notional value of a man-sievert saved may be as high as 10 5 : 1. The recommendation by NRPB, that dose limits for occupationally exposed people should be set by averaging over a period up to 10 years, is supported strongly; excessively restrictive annual dose limits do not in practice reduce average occupational exposures and may result in actual increases in collective occupational dose. Examples are given of the way in which the cost of reductions in occupational radiation exposure are managed in BNFL by delegation of financial authority to appropriate levels of management.
Reduction of dose in diagnosis B. F. Wall National Radiological Protection Board, Chilton, Didcot, Oxon The fact that medical X rays contribute about 90% of the total collective dose to the population of the UK from all man-made sources, testifies to the enormous benefit to the health of the nation that is attributed to this use of radiation by both the medical profession and the public. The overall effect of medical X rays is undoubtedly seen as an improvement in health care and to be of benefit, dose reduction in radiodiagnosis must be aimed only at unnecessary medical exposures. It is essentially this unbeneficial component of the collective medical dose that should be more properly compared with other sources of population exposure when assessing the relative urgency of directing resources at reducing them, since no other source of radiation exposure can claim to have the direct health benefit potential of medical radiology. This paper attempts to assess the extent of unnecessary medical exposures in the UK, which turns out to be substantial. Possibly as much as one third of the
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Proceedings of the British Institute of Radiology collective dose from medical X rays could be avoided without jeopardizing patient care. It goes on to determine the cost and effectiveness of a number of dose reduction methods. Many simple changes in procedure cost nothing while some dose saving improvements in equipment, like changing over to rare-earth screens, are also found to be extremely cost-effective and yet surprisingly have not received anything like universal adoption in the NHS. One reason for the low priority given to radiation protection in the health service may be the competition from other more effective methods of health care for the same limited resources. A rough comparison was made of the cost-effectiveness of some radiation protection options and a range of common medical procedures, in terms of the cost per quality adjusted life year saved (£/QALY). It indicated that even relatively expensive patient protection measures (like carbon fibre table tops) appear to compete favourably with a number of medical procedures that already consume large amounts of health service resources.
Radiation Protection: the environmental view Patrick Green Friends of the Earth, 26-28 Underwood Street, London Nl 7JQ For many years environmental groups have claimed that radiological protection standards underestimated the risk from
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exposure to ionizing radiation. A claim rejected by the nuclear industry and its regulatory authorities as unsupported by the scientific evidence. For such organizations the emphasis was on the ALARA principle (all doses must be kept as low as reasonably achievable) as the most effective way to reduce exposures, not changes in the dose limits. The latest evidence from the Radiation Effects Research Foundation in Japan has changed this. It is now accepted that risk estimates will rise and dose limits will have to be reduced. The question is when should they be changed and by how much? Following the International Commission on Radiological Protection's (ICRP) 1987 Statement that the new evidence was not sufficient to warrant an immediate change in its dose limits, the UK National Radiological Protection Board (NRPB) stated interim guidance was necessary. They recommended a threefold increase in the risk estimates for radiological protection purposes. Since then, at the Hinkley Point ' C Public Inquiry, they have recommended further increases in these risk estimates. These estimates differ from those suggested by Friends of the Earth only in terms of the Dose Rate Effectiveness Factor used. Next year, the ICRP are finally expected to publish their new recommendations. The ICRP's current system of radiological protection is based around three main features: (1) justification, (2) ALARA and (3) dose limits. This talk discusses this system in light of the increases in risk, and considers, from an environmental perspective, what changes should be made.
The British Journal of Radiology, May 1990
