Hoel David G
a Department of Public Health Sciences , Medical University of South Carolina , Charleston , SC , USA.
Int J Radiat Biol. 2018 Apr;94(4):307-314. doi: 10.1080/09553002.2018.1437483. Epub 2018 Feb 20.
Estimating cancer risks for continuous radiation exposures based upon data from acute exposures has been an important public health problem. A dose and dose rate effectiveness factor (DDREF) is typically used to estimate cancer risks for chronic exposures based upon risk estimates from acute exposures. A value of 2 for a DDREF has most often been used as proposed by the ICRP in ICRP60; however, an influential analysis of several cohorts concluded that there is no risk difference between acute and chronic exposures. It is the purpose of this article to analyze the recent nuclear worker studies and estimate the dose rate effectiveness factor, DREF, for solid cancers.
Twelve mortality studies were identified each with at least 100 cancer deaths and a meta-analysis was then carried out using their individual ratio of low dose rate cancer effect (LDR) to the corresponding high dose rate effect from the A-bomb cohort (LSS). The ratio is denoted by Q and its reciprocal is then an estimate of the DREF.
The result was Q= 0.36 (95% CI = 0.11, 0.60) and DREF = 2.63 (95% confidence interval [CI] = 1.61, 7.14). Clearly, this estimate is more consistent with a DREF of 2 than with a DREF of 1. The difficulty with the estimate Q = 0.36 is that it is driven by only two large and dissimilar worker studies, the INWORKS study (q = 1.14) and the Mayak worker cohort (q = 0.30). The higher exposures for these nuclear workers were often in the early years (e.g. before 1960) with exposures from neutrons and internal emitters that are not included in the risk analyses resulting in likely overestimation of cancer effects per dose which would increase the estimate of the DREF. The Mayak study did, however, adjust for plutonium exposures. Finally, consideration is given to other cohort studies where DREF values may possibly be determined, such as the environmental exposures to the Techa River area residents and the Chernobyl cleanup workers as well as medical X-ray workers. Although dissimilar an overall meta-analysis yielded a Q = 0.45 (95% CI = 0.24, 0.66).
It is concluded that the best estimate of a DREF is still about 2. However, because of the various problems with the epidemiology studies, especially their dosimetry, it is concluded that a DREF of about 2 should be accepted with considerable caution since it is driven solely by the Mayak study.
根据急性照射数据估算连续辐射照射的癌症风险一直是一个重要的公共卫生问题。剂量和剂量率有效性因子（DDREF）通常用于根据急性照射的风险估计来估算慢性照射的癌症风险。国际放射防护委员会（ICRP）在第60号出版物中建议，DDREF值通常采用2；然而，对几个队列的一项有影响力的分析得出结论，急性和慢性照射之间不存在风险差异。本文的目的是分析最近的核工业工人研究，并估算实体癌的剂量率有效性因子（DREF）。
确定了12项死亡率研究，每项研究至少有100例癌症死亡病例，然后对这些研究进行荟萃分析，使用它们各自的低剂量率癌症效应（LDR）与原子弹爆炸幸存者队列（LSS）相应的高剂量率效应的比值。该比值用Q表示，其倒数即为DREF的估计值。
结果为Q = 0.36（95%置信区间[CI] = 0.11，0.60），DREF = 2.63（95%置信区间[CI] = 1.61，7.14）。显然，这个估计值与DREF为2比与DREF为1更一致。估计值Q = 0.36的问题在于，它仅由两项规模大且不同的工人研究驱动，即INWORKS研究（q = 1.14）和玛雅克工人队列（q = 0.30）。这些核工业工人较高的照射剂量通常发生在早期（例如1960年之前），其照射源包括中子和体内发射体，而风险分析中未涵盖这些因素，这可能导致每剂量癌症效应的高估，从而增加DREF的估计值。不过，玛雅克研究对钚照射进行了调整。最后，考虑了其他可能确定DREF值的队列研究，如捷恰河流域居民的环境照射、切尔诺贝利清理工人以及医学X射线工作者。尽管各不相同，但总体荟萃分析得出Q = 0.45（95% CI = 0.24，0.66）。
得出的结论是，DREF的最佳估计值仍约为2。然而，由于流行病学研究存在各种问题，尤其是剂量测定方面的问题，得出结论认为，由于DREF仅由玛雅克研究驱动，因此对约为2的DREF应极为谨慎地接受。
