Nakamura Nori, Hirai Yuko, Kodama Yoshiaki, Hamasaki Kanya, Cullings Harry M, Cordova Kismet A, Awa Akio
Department of a Molecular Biosciences, 5-2 Hijiyama Park, Minami-ku, Hiroshima, Japan 732-0815.
b Statistics, Radiation Effects Research Foundation, 5-2 Hijiyama Park, Minami-ku, Hiroshima, Japan 732-0815.
Radiat Res. 2017 Oct;188(4):412-418. doi: 10.1667/RR14832.1. Epub 2017 Aug 11.
Retrospective estimation of the doses received by atomic bomb (A-bomb) survivors by cytogenetic methods has been hindered by two factors: One is that the photon energies released from the bomb were widely distributed, and since the aberration yield varies depending on the energy, the use of monoenergetic Co gamma radiation to construct a calibration curve may bias the estimate. The second problem is the increasing proportion of newly formed lymphocytes entering into the lymphocyte pool with increasing time intervals since the exposures. These new cells are derived from irradiated precursor/stem cells whose radiosensitivity may differ from that of blood lymphocytes. To overcome these problems, radiation doses to tooth enamel were estimated using the electron spin resonance (ESR; or EPR, electron paramagnetic resonance) method and compared with the cytogenetically estimated doses from the same survivors. The ESR method is only weakly dependent on the photon energy and independent of the years elapsed since an exposure. Both ESR and cytogenetic doses were estimated from 107 survivors. The latter estimates were made by assuming that although a part of the cells examined could be lymphoid stem or precursor cells at the time of exposure, all the cells had the same radiosensitivity as blood lymphocytes, and that the A-bomb gamma-ray spectrum was the same as that of the Co gamma rays. Subsequently, ESR and cytogenetic endpoints were used to estimate the kerma doses using individual DS02R1 information on shielding conditions. The results showed that the two sets of kerma doses were in close agreement, indicating that perhaps no correction is needed in estimating atomic bomb gamma-ray doses from the cytogenetically estimated Co gamma-ray equivalent doses. The present results will make it possible to directly compare cytogenetic doses with the physically estimated doses of the survivors, which would pave the way for testing whether or not there are any systematic trends or factors affecting physically estimated doses.
利用细胞遗传学方法对原子弹幸存者所接受剂量进行回顾性估计，受到两个因素的阻碍：一是原子弹释放的光子能量分布广泛，且由于畸变产额随能量变化，使用单能钴γ辐射构建校准曲线可能会使估计产生偏差。第二个问题是，自暴露以来，随着时间间隔的增加，新形成的淋巴细胞进入淋巴细胞池的比例不断上升。这些新细胞源自受照射的前体细胞/干细胞，其放射敏感性可能与血液淋巴细胞不同。为克服这些问题，采用电子自旋共振（ESR；或电子顺磁共振，EPR）方法估计牙釉质的辐射剂量，并与同一批幸存者通过细胞遗传学方法估计的剂量进行比较。ESR方法仅对光子能量有微弱依赖，且与暴露后的时间长短无关。对107名幸存者同时估计了ESR剂量和细胞遗传学剂量。后者的估计是基于这样的假设：尽管所检测的部分细胞在暴露时可能是淋巴干细胞或前体细胞，但所有细胞都具有与血液淋巴细胞相同的放射敏感性，且原子弹γ射线谱与钴γ射线谱相同。随后，利用个体DS02R1屏蔽条件信息，采用ESR和细胞遗传学终点来估计比释动能剂量。结果表明，两组比释动能剂量非常吻合，这表明从细胞遗传学估计的钴γ射线等效剂量来估计原子弹γ射线剂量，可能无需进行校正。目前的结果将使直接比较细胞遗传学剂量与幸存者物理估计剂量成为可能，这将为检验是否存在影响物理估计剂量的任何系统趋势或因素铺平道路。
