Abstract
BackgroundTo 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.MethodsA 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.ResultsBoth 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).ConclusionsUse of extremely narrow MLCs could increase dose homogeneity and conformity of the target volume for prostate VMAT.
Highlights
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
The results of both primary and boost plans showed that the dose homogeneity as well as target conformity could be improved by using MLCs with leaf width of 1.25 mm, which was simulated in this study
In this study we investigated the dosimetric advantage of fine resolution MLCs only on VMAT plans for prostate cancer, other tumor sites which could take advantage of MLCs with extremely narrow leaf width will be investigated as a future work
Summary
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. Several studies have investigated the relationship between MLC leaf width and the quality of IMRT plans [10,11,12]. They showed that finer leaf widths can result in more conformal dose distributions for target volumes and less dose delivered to normal tissue when the target volumes were small and IMRT was used. Rodal et al demonstrated that MLCs with fine leaf widths were
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