System construction of calculating the patient doses and its related cancer risk from CT examination in Japan

我们进行了一项全国范围的调查，以估计每年CT检查的频率。因此，CT检查的频率与医院床位数密切相关。以每家拥有CT设备的医院的床位数计算，日本2005年每年的CT频次约为2700万次。16岁以下儿童CT检查的频次可以用年龄相关频次的比例来估算，结果约为7.8万例。每次CT检查的器官剂量必须根据暴露条件和暴露区域进行估计。我们采用基于计算的方法，使用现有的程序，如ImPACT和CT- expo，因为不可能测量医院每次CT检查的剂量。计算数据与实测数据相吻合，部分器官剂量比实测值高出20%。目前使用LNT模型对低剂量和剂量率下辐射相关癌症风险的估计存在一些争议。然而，CT检查的剂量约为10毫戈瑞，目前尚不清楚几十毫戈瑞是否会给医疗目的暴露的儿童带来显著更高的过量癌症风险。为了研究CT使用对健康的影响，我们构建了一个计算与CT频率和剂量相关的癌症风险的系统。为了建立接触CT的儿童的随访队列，该系统将有助于根据剂量和CT频率等实际数据进行可能的解释。

We carried out a nation-wide survey to estimate the yearly frequency of CT examinations. As a result, the frequency of CT examinations was strongly correlated with the number of beds in hospital. When calculation was made using the number of beds in each hospital that has CT equipment, the yearly CT frequency of 2005 in Japan was estimated to be about 27 million. The frequency of pediatric CT examinations under 16 years old can be estimated using the proportion of age-dependent frequency and then resulted in about 78,000. The organ dose from each CT examination must be estimated based on the exposure condition and exposed region. We took calculation-based approach using available programs such as ImPACT and CT-EXPO, because it is impossible to measure the dose from each CT examination in hospital. The calculated data were validated by the measured data and then some organ doses showed 20% higher than measured. There are some controversies about current estimates of radiation-related cancer risk in low dose and dose rates using LNT models. However, the dose from CT examinations is about 10 mGy and it remains unclear whether several ten mGy would give a significant higher excess cancer risk to children exposed on medical purposes. To investigate the health effects of CT uses, we constructed a system of calculating cancer risk related with CT frequency and doses obtained by our results. To establish a follow-up cohort of children exposed to CT, this system would be useful for possible interpretation based on actual data such as doses and CT frequency.