固定铅门模式下容积旋转调强放疗与动态调强放疗在乳腺癌根治术后放疗中的比较

Comparison of VMAT vs d IMRT with fixed-jaw technique for postoperative radiotherapy of breast cancer

目的:探讨固定铅门模式下乳腺癌根治术后放疗中容积旋转调强放疗(VMAT)与动态调强放疗(d IMRT)的剂量学差异及技术特点。方法:选取左、右侧根治术后乳腺癌患者各10例,使用Raystation 4.7.5治疗计划系统制定VMAT计划和Eclipse 11.0治疗计划系统制定7野d IMRT计划,两种计划均采用合适的固定铅门技术,靶区处方剂量为50 Gy/25 F。比较两种计划的剂量学差异、机器跳数、治疗出束时间以及剂量验证γ通过率。结果:VMAT计划的靶区最大剂量、平均剂量、均匀性指数均优于d IMRT计划,前者剂量均匀性显著提升,且靶区内无剂量热点;两种计划的最小剂量、适形指数、靶区覆盖率基本相近(P>0.05)。主要危及器官双肺、心脏等的整体受照剂量VMAT计划明显低于d IMRT,尤其患侧肺的低剂量照射体积V_5、V_(20)及心脏的V_(30)显著降低;正常组织的整体受量VMAT计划偏高。VMAT计划单次照射的机器跳数比d IMRT平均减少了59%,治疗出束时间平均减少了60%。两种计划的γ通过率均满足治疗要求(>95%)。结论:两种技术均能满足临床处方要求,但VMAT技术具有更大的优势,其靶区剂量均匀性更好,可明显降低主要危及器官的整体受照剂量,尤其降低肺的低剂量照射体积,且显著减少机器跳数,缩短治疗时间。

Objective To explore the dosimetric differences and technology features of volumetric modulated arc therapy（VMAT） and dynamic intensity-modulated radiotherapy（d IMRT） with fixed-jaws technique for postoperative radiotherapy of breast cancer. Methods Twenty breast cancer patients after radical surgery were selected, with 10 cases of left-sided breast cancer and 10 of right-sided breast cancer. Raystation 4.7.5 treatment planning system and Eclipse 11.0 treatment planning system were used to design VMAT plans and 7-field d IMRT plans, respectively, with a target prescription dose of 50 Gy/25 F. Moreover, the most appropriate fixed-jaw technology was applied for the two plans of each patient. The dosimetric differences, monitor units, treatment time and gamma passing rate in dose verification were compared. Results VMAT plans were better than d IMRT plans in the maximum dose, mean dose, and homogeneity index of target areas, and the dose homogeneity of the former was significantly improved, without hot spots in target areas. The minimum dose,conformity index and target coverage of VMAT plans and d IMRT plans were basically similar（P〉0.05）. Compared with d IMRT plans, VMAT plans showed significantly decreased radiotherapy dose of major organs-at-risk, such as the whole lung and heart, especially the V5, V（20） of low dose region in the ipsilateral lung and the V（30） of the heart. The total dose of normal tissue in VMAT plans was slightly higher than that in d IMRT plans. Compared with those in d IMRI plans, the average number of monitor units was reduced by an average of 59% per fraction, and the treatment time was reduced by an average of 60% per fraction in VMAT plans. The gamma passing rate of VMAT plans and d IMRT plans met the requirement of treatment（95%）. Conclusion Both VMAT and d IMRT meet the requirements of clinical prescription, but VMAT has more advantages. VMAT can not only provide better dose homogeneity, significantly reduce the total dose of major organs-at-risk, especially the low dose volume of lungs, but also obviously decrease monitor units and shorten treatment time.