基于四维CT下胸部肿瘤调强计划中心脏和食道的剂量评估

Dose assessment of heart and esophageal in intensity modulated radiotherapy plan based on four-dimensional computed tomography for thoracic neoplasms

目的:基于四维CT(4DCT)探讨综合评估位置和体积不断改变的心脏和食道吸收剂量的方法。方法:将1个呼吸周期等分成10个时相点采集,重建得到的CT数据传至Pinnacle TPS工作站。定义各个时相下心脏和食道体积,统计分析其体积的变化特点;选用最大密度投影处理靶区,并设计放疗物理计划,统计心脏V40在10个呼吸时相中的变化,并作算术平均处理;统计食道最大剂量(Dmax)在10个呼吸时相中的变化,并以剂量最高的Dmax作为评估食道的指标。结果:心脏和食道体积随呼吸呈现出无规律变化的特点,心脏的变化最大可达14.7%,食道的可达24.4%;但体积的变化对心脏的V40和食道的Dmax的影响并不太大。结论:基于4DCT算术平均处理Vx和以剂量最高的Dmax作为评估指标可能是一种合理的处理方法。

Objective Based on four-dimensional computed tomography （4DCT）, to discuss on the way to comprehensively assess the absorbed doses of heart and esophageal with constantly changing locations and volumes. Methods One respiratory period was divided into ten time phase points. The CT data obtained from reconstruction were transmitted to Pinnacle treatment planning system workstation. The volumes of heart and esophagus at different time phases were defined, and the changing characteristics of volumes were statistically analyzed. The target region was processed by maximum intensity projection （MIP） reconstruction, and a radiotherapy plan was designed. The changes of heart V40 at ten time phases were statistically analyzed, and the arithmetic mean value was calculated. The changes of esophagus maximum dose （Dmax） at ten time phases were statistically analyzed, and the Dmax with the highest dose was used as the index to assess esophagus. Results The volumes of heart and esophagus showed irregular changes with respiration. The greatest change of heart was up to 14.7% and that of esophagus was up to 24.4%. However, volume variations had no significant impacts on heart V40 and esophagus Dmax. Conclusion The arithmetic mean of Vx based on 4DCT and the Dmax with the highest dose are taken as the evaluation indexes, which might be a reasonable processing method.