Aust. RBdiol(1978), 22,104

EDITORIAL

Occupational Radiation Dose Limit to the Embryo and Foetus P. L. T. ILBERY

I.C.R.P. 9 (1965)t recommended that under the remjyear rule dose accumulations a quarter for those occupationally exposed to radiation previously allowable up to 3 rem (3OmSv), should be limited to 1.3. It followed that the dose to the embryo during the critical first two months of organogenesis was less than 10mSv. The N.C.R.P. Report 352 recommended and 533 reiterated that during the entire gestation period the maximum permissible dose equivalent to the foetus from occupational exposure of the expectant mother should not exceed 4mSv. Despite the use of the permissive “should” terminology, the N.C.R.P. vigorously recommends efforts to bring exposure of the embryo and foetus to the very lowest practical level. Studies by the Radiation Effects Research Foundation of mental retardation, evident by 17 years, in children exposed in utem to the radiations from the atom bombs show significant effects at maternal doses of over 0.5 Gy at Hiroshima and 2 Gy at Nagasaki with prevalence rates higher for exposure in the sixth to fifteenthweek. Apparently during the first trimester radiation causes reduction in the number of brain-forming cells with secondary microcephaly and mental retardation if cell reduction is great enough. There is no doubt from investigations in laboratory animals4 that 0.5 - 1 Gy at any stage of gestation has an observable effect on the incidence of prenatal and neonatal deaths and malformations, and impairment of neurologic functions and behaviour was quoted in the BEIR Reports in offspring of pregnant animals with single doses as low as 250rnSv. In the diagnostic dose range (particularly at less than 0.1 Gy) it has not been possible to evaluate the incidence of effects of this kind, but it is unlikely that a threshold dose, if any,can be established. The confirmation or not of a threshold at very low levels depends on data which are inadequate and likely to remain so concerning doselresponse relationships despite the ability experimentally to controt doses at certain stages of development. As well as the difficulty in obtaining statistically significant numbers where an effect is not great, there is the added doubt in the carry over from rats or mice to man. There appears to be no (1 Gy = 100 rad; 1 Sv= 100 rem)

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question, however, that the foetus is especially sensitive to radiation even after the second month in utero.

In occupational exposure of the pregnant wornan the embryo-foetus enters the occupational radiation environment involuntarily. There is, hence, conflict with the right of the individual to perform the work she desires without restraint. However, in setting exposure at a maximum dose equivalent to the foetus of 5mSv, the N.C.R.P. shows that concern for radiation protection must be paramount. Where the mother is working with higher energy radiation this sets her own exposure nearer to SmSv than her present lawful 50mSv. There is the legal problem of the possibility of adverse effects arising where dose limits are exceeded when notification of pregnancy has not been agreed to be given to management. The employer could provide a monthly report to the employees on their radiation exposures, allowing women to apply for special consideration. Another option of employers, where practicable, is to keep the radiation dose of all radiation workers (including males) at a level comparable withthe N.C.R.P.’s recommended dose limit for the foetus. By lowering the dose limit from the occupational dose allowable per annum of 50mSv to SmSv, uniformity of radiation exposure could be achieved for the occupationally exposed, patients and other members of the public, and the embryo-foetus. However, where radiation workers can receive dose equivalents of 5mSv or more in short periods, it is obvious that potentially pregnant women should not be exposed to the same radiation environment as non-fertile women and men.

REFERENCES 1. I.C.R.P. Publication 9 (1965), Pergamon Press, Oxford. 2. N.C.R.P. Report No. 39 (1971), Basic Radiation Pro-

tection Criteria, Washington. 3. N.C.R.P. Report No. 53 (1977), Review of N.C.R.P. Radiation Dose Limit for Embryo and Foetus in Occupationally exposed Women, Washington. 4. Late Effects of Radiation, Eds. Fry, R. J. M. et al, Taylor & . Francis, London, 1970. 5. N.A.S. - N.R.C. (1972), Report of the Advisory Committee on the Biological Effects of Ionising Radiations, Washington.

AustrakzsianRadiology, Vol. XXII, No. 2, June, I 9 78

Occupational radiation dose limit to the embryo and foetus.

Aust. RBdiol(1978), 22,104 EDITORIAL Occupational Radiation Dose Limit to the Embryo and Foetus P. L. T. ILBERY I.C.R.P. 9 (1965)t recommended that...
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