以中国医用X射线工作者探索低剂量辐射致实体癌剂量效应关系

Dose-response relationship of cancer risks from low doses of ionizing radiation is main theoretical basis for establishing radiation protection dose limit, predicting lifetime cancer risks of populations, and for radioactive tumor etiology judgment of individuals with cancer who exposed to ionizing radiation occupationally. Now it mainly based on Atomic bomb survivors study (Life Span Study, LSS) who exposed to moderate to high doses and depends heavily on assumption of shape of dose response curve for low doses derived from laboratory studies. Actually, there are uncertainties in these assumptions. Now, 15-Country collaborative study of nuclear industry workers who suffered low dose exposure showed a much higher dose-response relationship of cancer risk than that derived from LSS. There is controversy for dose-response relationship of cancer risks for low dose. Our project intends to choose Chinese medical X-ray workers as our object of study. Since its dosage range covered doses of 15-country collaborative study, and it reached relative lower dose in LSS study. We prefer solid caners which have the most cases. We plan to do curve fitting and apply organ conversion factors to obtain personal organ cumulative dose based on doses estimated in early study, and to employ multivariate regression method to establish a solid cancer dose response risk model for CMXW. This work will provide important data for determination of dose-response of cancer risk attributable to low-dose ionizing radiation exposure. So far, we had obtained personal organ cumulative dose. Besides, we did a model fitting test, and had confirmed some candidate risk factors. The preliminary work will ensure this project successfully finished.

低剂量辐射致癌剂量效应关系，是为职业受照人群制定辐射防护剂量限值，预测其终生患癌风险和对其已患肿瘤个体进行放射病因判断的主要理论依据。现行依据主要根据中高剂量暴露人群日本原子弹爆炸幸存者研究和其外推低剂量效应所需的实验室研究。其中的外推假设存在较大不确定性。目前低剂量暴露人群15国核电站人群研究结果较上述结果高数倍。低剂量辐射致癌剂量效应存在较大争议。本项目拟选用‘跨越式衔接’了上述两人群剂量的中国医用X射线工作者队列为研究对象，首选发生例数最多的实体癌；拟采用曲线拟合和器官剂量转换的方法，在原剂量基础上估算个人器官累积剂量；拟采用多变量回归模型的分析方法，建立辐射致实体癌危险模型，为明确低剂量辐射致癌剂量效应关系提供重要参考。项目组前期研究工作已初步估算得到了个人器官累积剂量，并进行了危险模型预模拟，初步得到模型候选变量和模型框架，这为本项目顺利完成奠定了坚实的基础。

低剂量辐射致癌剂量效应关系，是为职业受照人群制定辐射防护剂量限值，预测其终生患癌风险和对其已患肿瘤个体进行放射病因判断的主要理论依据。现行依据主要根据中高剂量暴露人群日本原子弹爆炸幸存者研究和其外推低剂量效应所需的实验室研究。其中的外推假设存在较大不确定性。目前低剂量暴露人群15国核电站人群研究结果较上述结果高数倍。低剂量辐射致癌剂量效应存在较大争议。本项目选用‘跨越式衔接’了上述两人群剂量的中国医用诊断X射线工作者队列为研究对象，开展了低剂量辐射致实体癌危险研究。. 首先依据国际放射防护委员会74号出版物，确定该队列结肠剂量估算方法，估算其徽章剂量到结肠剂量的转移系数为0.3505，估算了其个人结肠累积剂量。该队列个人累积剂量呈左偏态分布，徽章剂量中位数为0.12Gy（均值为0.25Gy），结肠剂量中位数为0.042Gy(均数为0.086Gy)。队列60%成员结肠累积剂量小于0.05Gy，不足1%的成员结肠累积剂量大于0.5Gy。队列建立了辐射致实体癌危险模型，估算了其辐射致实体癌超额危险系数。结果显示队列成员在50岁患癌，结肠剂量尺度下，超额相对危险系数为0.87/Gy（95%CI, 0.48-1.45），超额绝对危险系数为22/104人年•Gy（95%CI, 14-32），二者P值均＜0.01。据此危险模型预估出该队列职业照射相关实体癌发生比例占20%。该比例在1955年之前开始工作组占42%，在1975-1980年间开始工作组占1%。. 本队列研究结果与15国核电站人群研究等低剂量队列研究结果具有一致性。与日本原子弹爆炸幸存者研究结果具有一致性，不支持其外推低剂量假设。该研究对改进当前职业照射辐射防护政策，提供了直接了职业人群数据参考。