Boice John D
a National Council on Radiation Protection and Measurements , Bethesda , MD , USA.
b Department of Medicine, Division of Epidemiology , Vanderbilt University , Nashville , TN , USA.
Int J Radiat Biol. 2017 Oct;93(10):1079-1092. doi: 10.1080/09553002.2017.1328750. Epub 2017 Jun 14.
The linear nonthreshold (LNT) model has been used in radiation protection for over 40 years and has been hotly debated. It relies heavily on human epidemiology, with support from radiobiology. The scientific underpinnings include NCRP Report No. 136 ('Evaluation of the Linear-Nonthreshold Dose-Response Model for Ionizing Radiation'), UNSCEAR 2000, ICRP Publication 99 (2004) and the National Academies BEIR VII Report (2006). NCRP Scientific Committee 1-25 is reviewing recent epidemiologic studies focusing on dose-response models, including threshold, and the relevance to radiation protection.
Recent studies after the BEIR VII Report are being critically reviewed and include atomic-bomb survivors, Mayak workers, atomic veterans, populations on the Techa River, U.S. radiological technologists, the U.S. Million Person Study, international workers (INWORKS), Chernobyl cleanup workers, children given computerized tomography scans, and tuberculosis-fluoroscopy patients. Methodologic limitations, dose uncertainties and statistical approaches (and modeling assumptions) are being systematically evaluated.
The review of studies continues and will be published as an NCRP commentary in 2017. Most studies reviewed to date are consistent with a straight-line dose response but there are a few exceptions. In the past, the scientific consensus process has worked in providing practical and prudent guidance. So pragmatic judgment is anticipated. The evaluations are ongoing and the extensive NCRP review process has just begun, so no decisions or recommendations are in stone.
The march of science requires a constant assessment of emerging evidence to provide an optimum, though not necessarily perfect, approach to radiation protection. Alternatives to the LNT model may be forthcoming, e.g. an approach that couples the best epidemiology with biologically-based models of carcinogenesis, focusing on chronic (not acute) exposure circumstances. Currently for the practical purposes of radiation protection, the LNT hypothesis reigns supreme as the best of the rest, but new epidemiology and radiobiology might change these conclusions. Stay tuned!
线性无阈（LNT）模型已在辐射防护领域应用了40多年，一直备受激烈争论。它严重依赖人类流行病学，并得到放射生物学的支持。其科学依据包括NCRP第136号报告（《电离辐射线性无阈剂量响应模型评估》）、联合国原子辐射效应科学委员会2000年报告、国际放射防护委员会第99号出版物（2004年）以及美国国家科学院的BEIR VII报告（2006年）。NCRP科学委员会1 - 25正在审查近期聚焦剂量响应模型（包括阈值模型）以及与辐射防护相关性的流行病学研究。
对BEIR VII报告之后的近期研究进行严格审查，这些研究包括原子弹爆炸幸存者、玛雅克工厂工人、原子武器老兵、捷恰河沿岸居民、美国放射技师、美国百万人研究、国际工人（INWORKS）、切尔诺贝利清理工人、接受计算机断层扫描的儿童以及接受结核荧光透视检查的患者。正在系统评估方法学局限性、剂量不确定性以及统计方法（和建模假设）。
研究审查仍在继续，将于2017年作为NCRP评论发表。迄今为止审查的大多数研究与直线剂量响应一致，但也有一些例外。过去，科学共识过程在提供实用且审慎的指导方面发挥了作用。因此预计会有务实的判断。评估正在进行，广泛的NCRP审查过程才刚刚开始，所以尚无定论或建议。
科学的发展需要不断评估新出现的证据，以提供一种虽不一定完美但却是最佳的辐射防护方法。LNT模型的替代方案可能即将出现，例如一种将最佳流行病学与基于生物学的致癌模型相结合的方法，重点关注慢性（而非急性）暴露情况。目前，出于辐射防护的实际目的，LNT假设作为其余最佳选择占据主导地位，但新的流行病学和放射生物学可能会改变这些结论。敬请关注！
