Wakeford R, Little M P
BNFL, Risley, Warrington WA3 6AS, UK.
Int J Radiat Biol. 2003 May;79(5):293-309. doi: 10.1080/0955300031000114729.
To review the estimates of the risk of childhood cancer per unit dose of radiation received in utero derived from the largest case-control study of obstetric X-ray examinations and to compare them with the childhood cancer risk coefficients obtained from the cohorts of Japanese atomic bomb survivors irradiated either in utero or as young children.
Data from the Oxford Survey of Childhood Cancers (OSCC) case-control study of foetal exposure to diagnostic X-rays and from the cohort studies of the Japanese survivors of the atomic bombings of Hiroshima and Nagasaki were used, together with associated dose estimates. Excess relative risk and excess absolute risk coefficients were compared, fully taking into consideration the various sources of uncertainty.
The excess relative risk coefficient for childhood (< 15 years of age) cancer obtained from the OSCC was around 50 Gy(-1), leading to an excess absolute risk coefficient for incident cases of about 8% Gy(-1). However, the statistical, dosimetry, modelling and other uncertainties associated with these risk estimates are appreciable, and there is reason to believe that these coefficients could be systematic overestimates. When these uncertainties and those associated with the equivalent risk coefficients derived from the Japanese cohort exposed in utero are taken into account, the risk estimates for childhood cancer obtained from these two sources are compatible. These coefficients are consistent with the high relative risk of childhood leukaemia among the Japanese survivors exposed as children. The absence of cases of childhood solid tumours among the Japanese children irradiated after birth in contrast to the significant excesses found in both intrauterine exposure studies might be explained by the cells from which these cancers originate being predominantly sensitive only to exposure in utero.
The consistency of the childhood cancer risk coefficients derived from the Oxford Survey and from the Japanese cohort irradiated in utero supports a causal explanation of the association between childhood cancer and an antenatal X-ray examination found in case-control studies. This implies that doses to the foetus in utero of the order of 10 mSv discernibly increase the risk of childhood cancer. However, uncertainties in risk estimates are such that it is difficult to conclude reliably from these epidemiological data what the level of risk at these low doses might be, beyond the inference that the risk is not zero or has been grossly underestimated.
回顾从最大规模的产科X线检查病例对照研究中得出的子宫内接受每单位剂量辐射后患儿童癌症风险的估计值，并将其与日本原子弹幸存者队列中在子宫内或幼儿期受到辐射后获得的儿童癌症风险系数进行比较。
使用了牛津儿童癌症调查（OSCC）关于胎儿暴露于诊断性X线的病例对照研究数据，以及广岛和长崎原子弹爆炸日本幸存者的队列研究数据，连同相关的剂量估计值。充分考虑各种不确定性来源，比较了超额相对风险系数和超额绝对风险系数。
从OSCC得出的15岁以下儿童癌症超额相对风险系数约为50 Gy⁻¹，导致发病病例的超额绝对风险系数约为8% Gy⁻¹。然而，与这些风险估计相关的统计、剂量测定、建模和其他不确定性相当可观，并且有理由相信这些系数可能存在系统性高估。当考虑到这些不确定性以及与子宫内暴露的日本队列得出的等效风险系数相关的不确定性时，从这两个来源获得的儿童癌症风险估计值是相符的。这些系数与儿童期受到辐射的日本幸存者中儿童白血病的高相对风险一致。与子宫内暴露研究中发现的显著超额病例形成对比的是，出生后接受辐射的日本儿童中没有儿童实体瘤病例，这可能是因为这些癌症起源的细胞主要仅对子宫内暴露敏感。
牛津调查和子宫内接受辐射的日本队列得出的儿童癌症风险系数的一致性，支持了病例对照研究中发现的儿童癌症与产前X线检查之间关联的因果解释。这意味着子宫内胎儿接受约10 mSv的剂量会明显增加儿童癌症的风险。然而，风险估计中的不确定性使得很难从这些流行病学数据可靠地得出这些低剂量下的风险水平可能是多少，只能推断出风险不为零或未被严重低估。
