肺癌固定剂量率旋转调强和容积旋转调强的剂量学分析

目的:通过对肺癌固定剂量率旋转调强放疗（IMAT）计划和容积旋转调强放疗（VMAT）计划的剂量学分析，为临床应用中肺癌VMAT放疗剂量率方式的选取提供参考。 方法:取11例肺癌患者，用RayStation计划系统设计IMAT和VMAT计划，比较其剂量学、机器跳数（MU）和治疗时间的差异。 结果:（1）11例肺癌患者的双弧IMAT和VMAT计划均能满足临床要求，IMAT和VMAT计划的靶区最小剂量D98%、最大剂量D2%、平均剂量（Dmean）、靶区均匀性指数、靶区适形度指数相近，无明显差异。靶区覆盖率VMAT计划好于IMAT计划。（2）危及器官受量:全肺的V5、V10、V20、Dmean和心脏的V20，VMAT计划比IMAT计划低。全肺的V30、心脏的V30、脊髓的最大剂量D1%，两种计划之间无明显差异。（3）正常组织在低剂量部分V5、V10、V15和Dmean，VMAT计划低于IMAT计划；V20、V25两种计划无明显差异；接近处方剂量部分V30、V35、V40，VMAT计划高于IMAT计划。（4）出束时间和MU:VMAT计划相比于IMAT计划，治疗出束时间大大减少，VMAT计划出束时间仅为IMAT计划出束时间的62%。两者的MU无明显差异。（5）两种计划的剂量验证通过率均大于95%，达到98.72%以上，能满足治疗要求。VMAT计划的剂量验证通过率略低于IMAT计划，相差约0.44%。 结论:VMAT技术相较于IMAT技术，其计划调制能力更强，可得到更优的靶区剂量分布，提高治疗效率，可以更好地保护危及器官，尤其是减少肺的低剂量照射体积。因此，在肺癌的旋转调强放射治疗中，VMAT技术相较于IMAT技术存在较大的优势。

Dosimetric analysis of intensity-modulated arc radiotherapy with fixed dose rate versus volumetric modulated arc therapy for lung cancer

Objective To analyze the dosimetric differences between intensity-modulated arc radiotherapy (IMAT) with fix dose rate and volumetric modulated arc radiotherapy (VMAT) for lung cancer, and provide reference for the selection of dose rate mode of VMAT for lung cancer. Methods IMAT and VMAT plans were designed for 11 patients with lung cancer using RayStation treatment planning system, and the differences in dosimetric parameters, monitor unit and delivery time were compared. Results Both dual arc IMAT and VMAT plans for lung cancer in 11 patients met the clinical requirements, and no significant differences were found in the minimum dose D98%, the maximum dose D2%, the average dose Dmean, homogeneity index and conformal index of target areas. However, the target coverage rate of VMAT plan was better than that of IMAT plan. The V5, V10, V20, Dmean of whole lung and the V20 of heart in VMAT were lower than those in IMAT plan, and the differences in the V30 of whole lung, the V30 of heart and the D1% of spine between IMAT and VMAT plans were not obvious. Compared with IMAT plan, VMAT plan had lower V5, V10 and V15 of normal tissues in the low-dose area, and normal tissues-Dmean, but higher V30, V35, V40 of normal tissues; two plans had no significant differences in the V20 and V25 of normal tissues. The delivery time of VMAT plan was greatly reduced, only 62% of that of IMAT plan. Two plans had similar monitor unit, without statistical differences. Though the dose passing rate of VMAT plan was slightly lower than that of IMAT plan, with a difference of about 0.44%, both the dose passing rates of the two plans were more than 98.72%, meeting treatment requirements. Conclusion Compared with IMAT, VMAT for lung cancer has a stronger plan modulation ability, can obtain better target dose distribution, improve the efficiency of treatment, and protect the organs-at-risk better, especially reducing the low-dose irradiation volume of lung. VMAT can bring more benefits to patients with lung cancer.