早期乳腺癌保乳术后仰卧及俯卧位调强放疗的剂量学比较

A dosimetric study of supine and prone treatment setups for breast cancer patients after breast conserving surgery

目的 比较早期乳腺癌保乳术后仰卧位与俯卧位调强治疗计划靶区和危及器官的剂量学差异.方法 选取15例接受保乳术后放疗的大乳腺及乳腺下垂的左侧乳腺癌患者,分别进行仰卧位及俯卧位CT定位扫描,利用相同优化条件分别进行切线2野调强治疗计划设计.比较2种不同体位计划的靶区剂量分布、心脏、左肺及右侧乳腺受照剂量和体积,以及机器跳数的差异.结果 俯卧位调强计划适形度指数（CI）优于仰卧位计划（0.79±0.05 vs.0.72 ±0.04,W=138,P＜0.01）,均匀性指数（HI）也优于仰卧位计划（1.09 ±0.01 vs.1.12±0.02,t=-4.7,P＜0.01）.俯卧位计划靶区接受95％处方剂量照射的百分体积（V95％）、最小剂量（Dmin）大于仰卧位计划（t=7.1、6.4,P＜0.01）,平均剂量（Dmean）大于仰卧位计划（W=153,P＜0.01）,最大剂量（Dmax）小于仰卧位计划（t=-3.6,P＜0.01）.仰卧位计划的右乳接受5 Gy照射的百分体积（V5）小于俯卧位计划（W=160,P＜0.01）,心脏接受30 Gy照射的百分体积（V30）大于俯卧位计划（t=5.4,P＜0.01）,心脏平均剂量（Dmean）、左肺接受20和5 Gy照射的百分体积（V20、V5）明显大于俯卧位计划（W=133、120、120,P＜0.01）.机器跳数间差异无统计学意义.结论 对于大乳腺及乳腺下垂乳腺癌患者,保乳术后俯卧位调强计划与仰卧位调强计划相比,靶区剂量分布更均匀,心、肺受照射剂量和体积明显减少.

Objective To compare the dosimetric differences of the targets and organs at risk （OARs） for early stage breast cancer patients receiving intensity modulated radiotherapy （IMRT） with supine or prone setups after breast conserving surgery.Methods After breast conserving surgery,15 left breast cancer patients with large and pendulous breasts were selected.Their planning CT images were acquired with supine and prone orientations respectively,based on which IMRT plans of 2 tangential fields were developed using the same optimization parameters.Treatment plans of the two setups were evaluated by comparing the target dose distribution,the doses and irradiated volumes of the heart,left lung,and right breast,and the monitor units （MUs）.Results Superior conformal index （CI） was observed in the plans of prone setup than the supine cases （0.79 ± 0.05 vs.0.72 ± 0.04,W =138,P 〈 0.01）.The homogeneity index （HI） of prone positioning was also better than that of supine setup （1.09 ±0.01 vs.1.12 ± 0.02,t =-4.7,P 〈0.01）.The planning target volume （PTV） receiving 95% of prescribed dose （V95%）,and the minimum doses （Dmin） of the prone cases were significantly higher than the supine patients （t =7.1,6.4,P〈0.01）.Higher mean doses （D） were observed in prone cases （W=153,P〈0.01）.The maximum doses （Dmax） of the supine plans were lower than the prone cases （t =-3.6,P 〈0.01）.The right breast volumes receiving 5 Gy doses or higher （V5） were less in the supine cases than the prone plans （W=160,P 〈0.01）.The heart volumes received no less than 30 Gy （V30）,D of the heart,and the left lung volumes received higher than 20 Gy or 5 Gy （V20,V5） of the supine plans were significantly higher than the prone cases （W =133,120,120,P 〈0.01）.No significant difference was observed on the MUs.Conclusions For cancer patients with large and pendulous breasts receiving IMRT after breast conserving surgery,prone setup leads to better homogeneity of target dose distribution,and reduces the doses and irradiated volumes of the heart and lungs.