不同布野方法对非小细胞肺癌调强放疗计划的影响

Impact of different beam set-up methods on quality of intensity modulated radiation therapy in nonsmall cell lung cancer

目的 探索非小细胞肺癌（NSCLC）调强放疗（IMRT）计划设计时不同的设野方法 对于计划质量的影响.方法 21例Ⅰ～Ⅲ期NSCLC患者进入本研究.IMRT采用固定野静态调强技术.每例患者采用不同的设野方法 共设计3套调强计划,分别为：IMRT-7,使用等角度的7个射野,射野的入射角度分别为0°、51°、102°、153°、204°、255°、306°;IMRT-5,使用等角度的5个射野,射野的入射角度为0°、72°、144°、216°、288°;IMRT-5m,使用不等角度的5个射野,设野的方法 为从前述IMRT-7的7个射野中去除2个野（若患者的病灶位于左肺,则去除角度为255°、306°的两野;若病灶位于右肺则去除角度为51°、102°的两野）.IMRT计划设计时正常肺剂量限制取之于同一患者实际治疗采用的3D-CRT计划肺V5～V60.IMRT开始取处方剂量为65 Gy,根据靶区和关键器官剂量要求按每2 Gy一阶梯进行递增或递减,直至获得最佳计划.结果 比较正常肺受量时发现,在V5～V25之间IMRT-5m的值较另两套计划均明显降低;V30～V40间3套计划相互间无明显差异;V45～V60间以IMRT-5计划最差;肺的平均剂量IMRT-5m最低.食管和脊髓的受量,靶区的适形性指数,以及治疗过程机器的总跳数3套计划间差异不明显.心脏V40以IMRT-5m计划的值最低.两两比较时,IMRT-5较IMRT-7明显增加了靶区的异质性指数值,而其他比较无明显差异.相比于3D-CRT,IMRT-7、IMRT-5和IMRT-5m分别可提高靶区剂量（5.1±4.6）Gy、（3.1±5.3）Gy和（5.5±4.8）Gy.结论 对于NSCLC的IMRT计划设计,射野方向是重要因素,调整好设野的方向可以减少照射野数目保证甚至提高IMRT计划的质量.

Objective To investigate whether the change of beam set-up methods will influence the dosimetric quality of intensity modulated radiation therapy （IMRT） for non-small cell lung cancer （NSCLC）.Methods Twenty-one stage Ⅰ-Ⅲ NSCLC patients were selected for this study.The technique of step and shoot was used and three different beam set-up methods were chosen for IMRT planning,including IMRT-7 with nine equal-spaced beams angled 0°,51°,102°,153°,204°,255°and 306°; IMRT-5 with five equal-spaced beams angled 0°,72°,144°,216°and 288°; and IMRT-5m which was created from IMRT-7 but excluded 2 fields （51°and 102° were omitted if there was lesion in the right lung,while 255°and 306° were excluded if there was lesion in the left lung）.The dose constrains ofnormal lungs for IMRT were set according to V5-V60 of normal lungs obtained from the same patient＇s actually treated 3D-CRT dose volume histogram.The prescription dose for IMRT started from 65 Gy,and then escalated or decreased step by step by 2 Gy once a time until the best plan was obtained.Results For normal lung dose,IMRT-5m had lower V5-V25 than the other two groups; but there was no significant difference in V30-V40.IMRT-5 was the worst for V45-V60; and mean lung dose was lowest in IMRT-5m.Dose parameters of esophagus and spinal cord,target conformity index,and total monitor units were all similar among difference plans.IMRT-5m had lowest heart V40 compared to the other two groups.For target heterogeneity index,IMRT-5 was higher than IMRT-7,but there were no significant differences among IMRT-5m,IMRT-5 and IMRT-7.Compared to 3D-CRT,the prescription dose could be increased by （5.1 ±4.6） Gy for IMRT-7,（3.1 ±5.3） Gy for IMRT-5,and （5.5 ±4.8）Gy for IMRT-5m.Conclusion Fewer beams and modified beam angles could result in similar,even better plan quality.