22. 尽管存在这些困难，但风险估计数在用于确定辐射照射对某个人群的影响方面具有重大价值。委员会 2000 年的报告为了风险预测目的，强调了根据受照年龄或已届年龄模拟由辐射引起的相对风险的各种模型。对于跟踪时期较长的研究来说，现在可以明显看出这些模型并不合适。委员会 2006 年的报告指出，如果固体癌死亡率风险模型所模拟的辐射照射导致的相对或绝对超高风险与受照以来时间和已届年龄的指数函数积成比例，那么这些模型即为最合适的模型。目前较受欢迎的白血病死亡率模型表明，相对的超高风险与受照年龄和已届年龄指数积成比例，绝对的超高风险则与受照以来时间指数成比例。如果将这些模型适用于各个年龄的五种人口（中国、日本、波多黎各、美利坚合众国和大不列颠及北爱尔兰联合王国）中的任何一种，则受 1 希沃特（希）急性剂量照射后所有固体癌的生命期死亡风险率约为 4.0-7.5%，白血病约为 0.7-1.0%。2006 年报告附件 A 中的计算表明，这些数值随着人口和风险模型的不同而有所变化；其中固体癌的变化最大。这些癌症风险估计数比以前在委员会2000 年报告中公布的数字要低，虽然低得不多。癌症风险估计数的有些降低可能是由于采用了新的原子弹剂量测定法和进行了跟踪所致，尽管更大一部分可能是由于采用了不同的风险预测和迁移模型，特别是对固体癌而言。儿童时受到照射的人口的生命期癌症风险估计数可能比所有年龄段受到照射的人口高 2至 3 倍。但持续跟踪受到辐照的现有存活人群对于确定生命期风险将会非常重要。对日本原子弹爆炸幸存者数据的分析结果与所有固体癌总体风险的线性剂
22. Despite these difficulties, risk estimates are of considerable value for use in characterizing the impact of radiation exposure on a population. The Committee’s 2000 report emphasized, for the purpose of risk projection, models that simulated the relative risk due to radiation according to age-at-exposure or attained age. With longer follow-up studies it has become clear that these models do not fit well. The Committee’s 2006 report indicates that best fits are currently obtained if the models for the risk of mortality from solid cancer simulate the relative or absolute excess risk due to radiation exposure as proportional to a product of functions involving powers of time since exposure and attained age. The current preferred leukaemia mortality models imply that the relative excess risk is proportional to a product of powers of age at exposure and attained age, and absolute excess risk is proportional to a power of time since exposure. When these models are applied to any of five specific populations (China, Japan, Puerto Rico, the United States of America and the United Kingdom of Great Britain and Northern Ireland) of all ages, the lifetime risk of death from all solid cancers together following an acute dose of 1 sievert (Sv) is estimated to be about 4.0-7.5 per cent, and for leukaemia 0.7-1.0 per cent. The calculations in annex A to the 2006 report show that these values vary among different populations and with different risk models; the variation being most substantial for solid cancers. These cancer risk estimates are somewhat lower, although not by much, than those previously published in the Committee’s 2000 report. Some of the reduction in cancer risk estimates may be due to the new atomic bomb dosimetry and follow-up, although a larger part is probably due to the different risk projection and transport models used, in particular for solid cancers. Lifetime cancer risk estimates for those exposed as children might be a factor of 2 to 3 times higher than the estimates for a population exposed at all ages. However, continued follow-up of existing irradiated cohorts will be important in determining lifetime risks. The results from analysing the data