Park Jong Min, Park So-Yeon, Kim Jin Ho, Carlson Joel, Kim Jung-In
Department of Radiation Oncology, Seoul National University Hospital, Seoul, South Korea.
Institute of Radiation Medicine, Seoul National University Medical Research Center, Seoul, South Korea.
Radiat Oncol. 2016 Jun 23;11:85. doi: 10.1186/s13014-016-0664-0.
To investigate the effect of multi-leaf collimators (MLCs) with leaf width of 1.25 mm on the plan quality of volumetric modulated arc therapy (VMAT) for prostate cancer.
A total of 20 patients with prostate cancer were retrospectively selected. Using a high definition MLC (HD MLC), primary and boost VMAT plans with two full arcs were generated for each patient (original plan). After that, by shifting the isocenter position of the 2nd arc by 1.25 mm in the cranio-caudal direction, we simulated fluences made with MLCs with leaf width of 1.25 mm. After shifting, primary and boost plans were generated for each patient (shifted plan). A sum plan was generated by summation of the primary and boost plan for each patient. Dose-volumetric parameters were calculated and compared.
Both the homogeneity index (HI) and conformity index (CI) of the shifted plans were better than those of the original plans in primary plans (HI = 0.065 vs. 0.059 with p < 0.001 and CI = 1.056 vs. 1.044 with p = 0.006). Similarly, the shifted plans for the boost target volume showed better homogeneity and conformity than did the original plans (HI = 0.060 vs. 0.053 with p < 0.001 and CI = 1.015 vs. 1.009 with p < 0.001). The target mean dose of the original plans was closer to the prescription dose than that of the shifted plans in the case of sum plans (81.45 Gy vs. 81.12 Gy with p = 0.001).
Use of extremely narrow MLCs could increase dose homogeneity and conformity of the target volume for prostate VMAT.
探讨叶宽为1.25 mm的多叶准直器（MLC）对前列腺癌容积调强弧形放疗（VMAT）计划质量的影响。
回顾性选取20例前列腺癌患者。使用高清MLC（HD MLC）为每位患者生成具有两个完整弧形的原发和追加VMAT计划（原始计划）。之后，通过将第二个弧形的等中心位置在头脚方向上移动1.25 mm，模拟叶宽为1.25 mm的MLC产生的注量。移动后，为每位患者生成原发和追加计划（移动计划）。通过将每位患者的原发计划和追加计划相加生成总和计划。计算并比较剂量体积参数。
在原发计划中，移动计划的均匀性指数（HI）和适形指数（CI）均优于原始计划（HI = 0.065对0.059，p < 0.001；CI = 1.056对1.044，p = 0.006）。同样，追加靶区体积的移动计划比原始计划显示出更好的均匀性和适形性（HI = 0.060对0.053，p < 0.001；CI = 1.015对1.009，p < 0.001）。在总和计划的情况下，原始计划的靶区平均剂量比移动计划更接近处方剂量（81.45 Gy对81.12 Gy，p = 0.001）。
使用极窄的MLC可提高前列腺VMAT靶区体积的剂量均匀性和适形性。
