乳腺癌改良根治术后胸壁电子线照射研究

摘要

Objective: To find out the dosimetry characteristic of EBCWI in postmastectomy patients with breast cancer for rational application in clinical practice. Methods : This study was base on CT images of 10 postmastectomy patients with left breast cancer, and with the use of Eclipse 8. 6 3D - TPS ( matching with Varian Clinac iX accelerator ). Clinic target volume( CTV ),lungs and heart were confirmed by senior radiotherapy doctors, treatment plans were designed to simulate BCWI using different irradiation energy from different gantry angles. Dose distribution and DVH were evaluated. Furthermore, boluses were used for more ideal results. Results: Better dose distribution and higher mean dose of CTV ( CTVmean ) occurred in EBCWI plans by 20° - 40°gantry angles. The prescription of 50 Gy gave to 95％ CTV ,was unable to be achieved by 6MeV electron beam; When using 9 MeV ,12MeV and 15MeV electron beam, volume of ipsilateral lung received≥20Cy ( LungV20 ) were 31％ ±6％ , 50％ ±4％ and 65％ ±8％ , and volume of heart that received≥30Gy ( HeartV30 ) were 10％ ±2％ , 23％ ±3％ and 38％ ±5％ , respectively; Irradiation dose of lung and heart had reduced obviously by excelsior boluses application while CTV dose had little change. Conclusion : EBCWI by energy between 9MeV and 12MeV from about 30° ipsilateral gantry angle are better selection in postmastectomy patients with breast cancer. And boluses should be correctly applied to optimize dose distribution.%目的:探讨乳腺癌改良根治术后胸壁电子线照射(electron beam chest wall irradiation,EBCWI)的剂量学特点,为临床应用提供参考.方法:以10例左乳癌改良根治术后的定位CT图像为基础,借助Eclipse 8.6三维治疗计划系统软件(Varian Clinac iX 加速器配备)进行EBCWI剂量学研究.由资深放疗医师确定CTV和心脏及肺组织边界,模拟制定不同能量电子线以不同机架角方向实施胸壁照射的放疗计划.评价各治疗计划的剂量分布和靶区及心肺组织的体积剂量关系(DVH),并尝试用Bolus优化计划结果.结果:从照射角度来看,20°-40°机架角治疗计划的剂量分布较好并且靶区平均剂量(CTVmean)较高.从射线能量分析,以95%CTV 50Gy为处方剂量,6MeV电子线无法达到剂量要求;9MeV、12MeV和 15MeV电子线在满足靶剂量时,同侧肺≥20Gy的体积百分比(LungV20)分别为31%±6%、50%±4%和65%±8%;心脏≥30Gy的体积百分比(HeartV30）分别为10%±20%、23%±3%和38%±5%;精心设计Bolus可以显著降低心肺组织剂量而对靶区剂量几无影响.结论:乳癌根治术后EBCWI宜选择9-12MeV电子线从偏患侧30°左右的机架角实施照射,并恰当应用Bolus以进一步优化剂量分布.rn照射,并应恰当应用月燥造怎泽以进一步优化剂量分布.