Radiological hazards to patients / interim report of the Committee.

  • Great Britain. Committee on Radiological Hazards to Patients
Date:
1959
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Licence: Public Domain Mark

Credit: Radiological hazards to patients / interim report of the Committee. Source: Wellcome Collection.

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    value of 10 milliroentgens per year given by the United Nations Scientific Committee for a population, in which 10 per cent are examined by mass radio- graphy each year.?® 20. The Report of the United Nations Scientific Committee emphasises that ‘“‘ any present attempt to evaluate the effects of sources of radiation to which the world population is exposed can produce only tentative estimates with wide margins of uncertainty ’’.2 Nevertheless, the Report includes a calculation of what is considered an upper limit to the number of leukaemia cases produced by a given radiation exposure, on the basis that “‘ the increased incidence per rem would be 1-5 per 1 million per year for the rest of the lives of the exposed. individuals ”.“ This calculation is a generalisation from observations on leukaemia following high doses, and evidence is as yet lacking that the calcula- tion is equally applicable to the very low doses associated with mass radiography. Indeed, as the United Nations Scientific Committee has stated, there may be no addition at all from this source to the incidence of leukaemia. 21. Nevertheless, applying these same calculations to the mean marrow dose per year in Great Britain, leads to the conclusion that indefinite continuation of mass miniature radiography at the present rate could produce annually at the most 20 cases of leukaemia additional to the present annual incidence from all causes of about 2,500 cases, but might produce none at all. Similar considera- tions show that an individual who has ten mass miniature radiography examina- tions over a series of years would have his chance of developing leukaemia in any year increased—if at all—from 50 in a million to at most 51. 22. We are satisfied that the somatic risk of doses at these levels is on any interpretation far outweighed by the benefits of mass miniature radiography.* Review of the Use of Mass Miniature Radiography 23. The Committee in the course of its review concluded that modifications of mass miniature radiography units might be made which would reduce still further the radiation dose to the patient. Details of the modifications which were recommended for immediate implementation are given in Appendix III. 24. Also in the course of our work some incidental observations on persons in the queue awaiting their turn for examination showed that those lined up close to the side of the apparatus might sometimes receive radiation during the waiting period. We have not investigated this matter further because we are informed that steps were immediately taken to prevent this occurring in future. (Appendix III (iv).) * Our measurements show that the gonadal dose is less than that calculated in 1952. In that year it was estimated to be less than 0:02 mr per head of population per year. From natural sources the annual dose received by an individual would increase by about 20 mr on going from a stone house in a limestone district to a granite house in a granite area (local gamma ray increment), or going from sea level to live at an altitude of 5,500 feet (cosmic ray increment). A per capita dose of 7 mr (the measured annual marrow dose in our Mass Miniature Radiography survey) would be equivalent to the increased dose after some 4 months residence in a granite district or at 5,500 feet. It is possible that an amount of radiation given in a single brief exposure at high intensity may be more damaging than the same amount given at a low intensity over a long time, but there is insufficient evidence on which to assess the effect of dose rate on these comparisons. The calculations in paragraph 21, however, are based on observations of leukaemia induction at about the same order of dose rate as in Mass Miniature Radiography. The uncertainties here lie in assumptions which are made in extrapolating from high doses to doses some 10,000 times smaller. 7
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