用于Monte Carlo临床剂量计算的CT数转换方法

Monte Carlo计算方法已在精确放疗剂量计算中广泛应用,为达到更高的计算精度需要有更准确的CT转换方法。传统简单分组CT转换方法由于元素组成转换太粗略,不能满足计算精度要求。该文根据人体主要的组织分区进行元素组成分析,引入混合转换方法,在骨骼区和软组织区使用曲线拟合方法对磷钙和碳氧氮元素进行转换;在肺组织区间,使用插值法简单有效地反映了从空气到肺再到软组织过渡中元素组成的变化。CT转换精度的提高使得整个剂量计算的相对误差在2.5%以内,从而使更加精确的治疗得以实施。

CT number conversion method for Monte Carlo dose calculations in radiotherapy

The Monte Carlo method is widely used for dose calculations in advanced radiotherapy. However, a more accurate CT conversion method is needed to reduce calculational errors. The elemental weights conversion method used in the traditional group CT conversion method is too simple and the dose calculational errors offen exceed the accuracy limits for modern radiotherapy. The mixed conversion method was developed to improve the conversion accuracy by grouping similar human body tissues. For bone tissue and soft tissues, linear curve fits were used to improve the conversion accuracies for phosphor, calcium, carbon, oxygen and nitrogen. For lung tissues, interpolation functions were used to describe the weight shifting from air and lungs to soft tissue. The improved accuracy of the CT conversion makes the entire dose calculation relative error to be within 2.5% which will enable more accurate radiotherapy.