Are Atomic-Bomb Dose-Response Data from ABCC/RERF Reasonable for Assessment of Radiation Risk?

Transcription

1 Are Atomic-Bomb Dose-Response Data from ABCC/RERF Reasonable for Assessment of Radiation Risk? O. Yamamoto Hiroshima International University, Kurose, Hiroshima , Japan INTRODUCTION Ever since Atomic Bomb Casualty Commission (ABCC) was established in 1948, the Unified Program, conceived in 1955 and a fixed population sample (Life Span Study extended) was selected from the Atomic Bomb (A-bomb) Survivors Supplementary Schedules of 1950 National Census, originally consisted of approximately 110,000 persons in Hiroshima and Nagasaki. Since 1958, the AHS, a fixed sub-sample of LSSextend sample, originally consisting of nearly 20,000 persons (1,2), has been followed for long-term clinical examinations for any late ionizing radiation effects of the A-bombs. AHS participants are thus provided complete physical examinations and laboratory tests during their biennial cycle visits to the ABCC/Radiation Effect Research (RERF) clinics. The AHS sample includes persons not-in-the cities (NIC) as the control groups. On the basis of the survey of the fixed population sample, ABCC/RERF have published many papers upto the present. These data became the basis for reports of the International Commission on Radiological Protection (ICRP) (3,4), the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) (5,6), and the Committee on the Biological Effects of Ionizing Radiation (BEIR) (7). The author would like to raise a question whether the use of ABCC/RERF data was reasonable or not. DOSE-RESPONSE CURVE Based on the cancer incidence in Hiroshima and Nagasaki A-bomb survivors, a linear-no threshold (LNT) model that radiation risk is always proportional to dose, no matter how small, was adopted by ICRP (3,4), UNSCEAR (5,6), and BEIR (7) for the assessment of risk at low doses and for recommendation of dose limits. Thompson et al. (8) reported the cancer incidence in A-bomb survivors, A linear dose-response relationship was expressed for all solid cancers. In the ABCC/RERF study, however, abscissa of dose-response curves is dose from A-bomb with no consideration of dose-rate in spite that the dose-rate is a great factor for the incidence. Incidence is affected not only with radiation dose but also with radiation dose-rate, both of which are in inverse proportion to distance from the A-bomb explosion center. For example, the dose-rate at 1 km from the center is 1/100 compared to that at 100 m as well as the dose, that is, the patients were exposed to the radiation at the different dose-rates depending on the distance. Dose-response has to be compared at the same dose-rate. This is a basic dogma in radiation chemistry or radiation cell biology. From this point of view, dose-response curves reported by ABCC/REFF are not correct. The basic dogma has not been applied to human, which is very mysterious and a great mistake for assessment of radiation risk. Real animal experimental data are shown in Fig. 1, which was rearranged from data of our paper (9,10) studied the biological effects of tritiated water (HTO) on mice. Figure 1 shows the relationship of the incidence of thymic lymphoma and the life shortening to the dose at various dose-rates. The response can be found to be clearly different at different dose-rates. Also threshold dose-rate was found not only for thymic lymphoma development but also life shortening showing sigmoidal relationship (9,10). Dose on abscissa of data from ABCC/RERF is dose at different dose-rates. Such expression of dose is inadequate. It has to be corrected to (Dose) dose-rate factor as shown in Fig. 2. Therefore, ICRP should use the term (Dose) dose-rate factor but not the term Dose for radiation risk estimation. 1

2 Fig. 1. Difference of the incidence of thymic lymphoma and the life shortening at different dose-rate for mice administered tritiated water. This figure was arranged from data of Yamamoto et al. (9,10). Fig. 2. Correction of dose-response curve reported by ABCC/RERF, changing Dose to (Dose) dose-rate factor as the term for radiation risk. Dotted line: no data or uncertain dose area. Arrow mark: threshold. CONTAMINATION BY MEDICAL RADIATION DOSE The contaminated medical radiation dose is not included in dose in ABCC/RERF reports. Indeed, not only the NIC subjects but also the A-bomb exposed group subjects have received the diagnostic medical X-rays routinely in ABCC/RERF and occasionally in hospitals and clinics. The A-bomb exposed subjects were divided to three groups (10~99 mgy exposed, 100~999 mgy exposed, and >1,000 mgy exposed). Our medical X-ray dosimetry program was begun in 1962 for the purpose that the potential contamination by medical X-ray exposure must be taken into consideration to avoid erroneous conclusions in the studies for late A-bomb effects. Doses incurred to the surface, active bone marrow, gonads, and other organs during various radiological procedures were calculated based on phantom human dosimetry (11-16). Radiological practices in other hospitals and clinics (11,17-24) and trends in radiological practice were assessed in Hiroshima and Nagasaki (21,23). The reliability of AHS subjects' responses to questions during interviews and the changes in use of fluoroscopic apparatus from conventional to image intensifier types are among the topics which have been studied because of their marked influence on the doses incurred. 2

3 All medical X-ray data were entered and stored on computer tapes, including subject identification, date, site and type of examination, hospital name, and bone marrow, gonad, and skin doses. Medical X-ray doses from radiological examinations inside (25) and outside (26) RERF were routinely recorded, and were available for periodic analysis. A report has been published in 1988 as the initial analysis for potential contamination of A- bomb doses by medical X-ray doses received by the members in the AHS sample through the end of 1982 (27). The most contributed X-ray dose was by the upper GI series fluoroscopy. Fig. 3. Distribution of medical X-ray exposure doses, female gonad doses (A-bomb exposed and not-incity, Hiroshima and Nagasaki) at the end of This figure was reproduced from data of Yamamoto et al. (27). The male gonad doses are lower than the bone marrow doses and the female gonad doses because of the position outside body. The bone marrow doses are relatively lower than female gonad doses being due that bone marrow exists not only in the body but also in the legs and arms. The female gonad dose can correspond to the most precisely to the body dose. Among the three exposed groups of subjects, the average dose was almost the same though that of NIC group was slightly low. Distribution of medical X-ray doses in total is shown in Fig. 3. More than 50% of subjects were exposed to 50~250 mgy of medical X-ray dose. 3

4 Fig. 4. Contamination rates of T65DR by medical X-ray exposure doses, female gonad doses (Hiroshima and Nagasaki) at the end of The mean contamination rate was 54% from data of Yamamoto et al. (27). Contamination rate of A-bomb dose by female gonad X-ray doses for the lowest A-bomb dose group is shown in Fig. 4. In average, the contamination rate is 25%. Sixteen percent of subjects has more than 100% contamination and a few percent has % contamination. This result was obtained at the end of The contamination rate at the present has to be much more. Such contamination rate for the lowest A-bomb exposed group is very serious for assessment of radiation risk. Even for the middle A-bob exposed group, the contamination rate is still effective, though it is very low for the highest A-bomb dose group. Not only A-bomb but also medical X-ray is acute irradiation. The medical X-ray has to be also effective as well as the A-bomb. The analysis of A-bomb radiation effect without medical X-ray dose may increase more the uncertainty when A-bomb dose is lower. That is, the radiation risk of the low A-bomb exposed subjects may be very obscure when the medical X-ray doses are not taken into consideration for the correction at least to the subjects exposed to A-bomb dose less than 0.1 Gy. REFERENCES 1. G.W.Beebe and M.Usagawa, ABCC Tech, Rep (1968). 2. J.L.Belsky, K.Tachikawa, S.Jablon, Yale J. Biol. Med. 46, (1973). 3. ICRP, Annals of the ICRP. Publication No. 30, vol 2, pp. 5-7, Pergamon Press, Oxford (1979). 4. ICRP, Annals of the ICRP. Publication No. 60, pp , Pergamon Press, Oxford (1990). 5. UNSCEAR, 1977 Report to the General Assembly with annexes. United Nations, New York (1977). 6. UNSCEAR, 1993 Report to the General Assembly with annexes. United Nations, New York (1993). 7. BEIR, BEIR V. National Academy Press, Washington DC (1990). 8. D.E.Thompson, K.Mabuchi, E.Ron, M.Soda, M.Tokunaga, S.Ochikubo, S.Sugimoto, T.Ikeda, M.Terasaki, S.Izumi and D.L.Preston, Radiat. Res. 137, S17-S67 (1994). 9. O.Yamamoto, T.Seyama, A.Ito and N.Fujimoto, Int. J. Radiat. Biol. 73, (1998). 10. O.Yamamoto and T.Seyama, Proceedings of International Meeting on Biological Effects of Low Dose Radiation, Cork, Ireland, 1999 (Eds. T.Yamada, C.Mothersill, B.D.Michael and C.S.Potten). Elsevier, Amsterdam, in press. 11. H.Yoshinaga, Y.Ihno, W.J.Russell, S.Antoku and M.Mizuno, ABCC Tech. Rep (1966). 12. H.Yoshinaga, K.Takeshita, S.Sawada, W.J.Russell and S.Antoku, Br. J. Radiol. 40, (1967) 13. S.Antoku and W.J.Russell, Radiology. 10, (1971). 4

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