重复CT模拟定位分析肿瘤体积变化对鼻咽癌调强放疗的影响

目的 利用重复CT模拟定位分析肿瘤体积变化对鼻咽癌调强放疗的影响。 方法 选取2011年7月至2012年11月期间20例鼻咽癌调强放疗的患者,于放疗前进行首次CT模拟定位,放疗中在患者接受30 Gy剂量照射时进行重复CT模拟定位扫描。在治疗计划系统将首次扫描的CT图像与重复扫描的CT图像进行融合,计算GTV体积的退缩率;在重复CT图像上利用原计划重新计算剂量分布,根据剂量体积直方图,分别计算出危及器官脑干和脊髓的受量变化。 结果 重复CT模拟定位比较首次CT模拟定位GTV体积平均退缩率为28.7%。重复CT模拟定位比首次CT模拟定位脑干和脊髓的单次最大剂量、1 cm³体积的剂量和平均剂量的百分比均有所增加(t=0.83~3.17,P<0.05)。 结论 利用重复CT模拟定位发现,鼻咽癌调强放疗患者在接受30 Gy剂量照射时,GTV体积的退缩率较明显,进而导致危及器官剂量的增加。

Influence of tumor volume change on intensity modulated radiotherapy for nasopharyngeal carcinoma analyzed by repeated CT simulation

Objective To analyze the influence of tumor volume change on intensity modulated radiotherapy (IMRT) for nasopharyngeal carcinoma by analyzing the repeated CT simulation. Methods Twenty nasopharyngeal carcinoma patients undergoing IMRT from July 2011 to November 2012 were selected in the study. The first CT simulation was conducted prior to radiotherapy, and the repeated CT simulation was finished after radiotherapy of 30 Gy. The first and the repeated CT images were fused in treatment planning system and GTV volume shrink rate was calculated. The original plan was used to recalculate the dose distribution on repeated CT. The dose volume histogram was used to calculate the dose difference of organs at risk including the brain stem and spinal cord. Results Compared with the first CT, GTV volume shrink rate of the repeated CT simulation was 28.7%, the maximum dose, 1 cm³ volume and the average dose percentage of the brain stem and spinal cord were increased (t=0.83-3.17,P<0.05). Conclusions GTV volume shrinked significantly after radiotherapy of 30 Gy in IMRT for nasopharyngeal carcinoma. The dose of the organs at risk increased accordingly.