Walsh Linda, Schneider Uwe
Department of Physics, Science Faculty, University of Zürich, Winterthurerstrasse 190, 8057, Zurich, Switzerland.
Radiat Environ Biophys. 2016 Nov;55(4):509-515. doi: 10.1007/s00411-016-0667-0. Epub 2016 Sep 1.
Determinations of the lowest colon dose, D , below which there is a statistically significant excess relative risk of all solid cancer, when analyses are restricted to the range [0, D ], are of current interest in research related to radiation protection and risk assessment. In reviewing recent cancer mortality reports on the Life Span Study (LSS) of Japanese A-bomb survivors, reported D values were found to vary between different reports. The report 12 (follow-up: 1950-1990) found a D of 50 mGy, but the most recent report 14 (follow-up: 1950-2003) found a D of 200 mGy. There were small dosimetry changes between report 12, which used DS86, and report 14, which used DS02, but these changes are unlikely to account for a difference in D of a factor of 4. This short communication examines the reasons for this difference in D by presenting further investigations into D using different trial values for D and various follow-up time spans, all with the same DS02 dosimetry. Magnitudes of the low-dose risks in different dose ranges are also presented. It is shown here that the main influence on D comes from the length of follow-up and a D of 50 mGy may also be obtained with the most recent LSS mortality data and DS02, if a restricted follow-up is analyzed. A systematic trend was evident of lower D values for earlier mortality follow-up periods, consistent with information from earlier LSS reports. Although it may seem surprising that the D increases with longer follow-up and better statistics, this systematic trend appears to be a consequence of decreasing mortality risks with longer follow-up, even though the error bars on the risks are getting smaller with increasing follow-up. These systematic trends also persisted after accounting for differences between baseline cancer rates for two groups of survivors who were either proximal or distal to the A-bomb hypocenter. Similar systematic trends, although much less pronounced, were also found in the LSS cancer incidence data. Some evidence is provided here that results on low-dose radiation risks from earlier follow-up periods should not be ignored by radiation protection authorities, once the results from the new extended follow-ups are published. This is because of the possibility that the new data for extended follow-up beyond a certain calendar time, which pertain to very long times since exposure, may be contributing to an overall reduction in radiation related risks per unit dose compared to analogous risks determined from earlier follow-up periods, because of the risk effect modification of time since exposure.
确定最低结肠剂量(D)具有当前辐射防护和风险评估研究的意义，在分析限于范围([0, D])时，低于该剂量会出现所有实体癌统计学显著的超额相对风险。在审查日本原子弹幸存者寿命研究（LSS）的近期癌症死亡率报告时，发现不同报告中的(D)值有所不同。报告12（随访时间：1950 - 1990年）得出的(D)值为50毫戈瑞，但最新报告14（随访时间：1950 - 2003年）得出的(D)值为200毫戈瑞。使用DS86的报告12和使用DS02的报告14之间剂量测定有小的变化，但这些变化不太可能解释(D)值相差4倍的差异。本简短通讯通过使用不同的(D)试验值和各种随访时间跨度对(D)进行进一步研究来探讨(D)值差异的原因，所有研究均采用相同的DS02剂量测定法。还给出了不同剂量范围内低剂量风险的大小。结果表明，对(D)的主要影响来自随访时间长度，并且如果分析受限随访，使用最新的LSS死亡率数据和DS02也可能得到50毫戈瑞的(D)值。对于早期死亡率随访期，(D)值较低的系统趋势明显，这与早期LSS报告的信息一致。尽管随着随访时间延长和统计数据更好，(D)值增加可能令人惊讶，但这种系统趋势似乎是随访时间延长导致死亡率风险降低的结果，即使风险的误差条随着随访增加而变小。在考虑原子弹爆炸中心近端或远端两组幸存者的基线癌症发病率差异后，这些系统趋势仍然存在。在LSS癌症发病率数据中也发现了类似的系统趋势，尽管不太明显。这里提供了一些证据表明，一旦新的延长随访结果公布，辐射防护当局不应忽视早期随访期关于低剂量辐射风险的结果。这是因为，与从早期随访期确定的类似风险相比，在特定日历时间之后的延长随访新数据可能导致每单位剂量辐射相关风险总体降低，这是由于暴露后时间对风险效应的修正。
