Volumetric modulated arc therapy with dynamic collimator rotation for improved multileaf collimator tracking of the prostate

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• 作者：Ghulam Murtaza^a ; ^b ; Jakob Toftegaard^a ; Ehsan Ullah Khan^b ; ^c ; Per Rugaard Poulsen^a ; ^{per.poulsen@rm.dk}
• 关键词：IGRT ; Prostate motion ; MLC tracking
• 刊名：Radiotherapy and Oncology
• 出版年：2017
• 出版时间：January 2017
• 年：2017
• 卷：122
• 期：1
• 页码：109-115
• 全文大小：1552 K
• 卷排序：122

文摘

To improve MLC tracking of prostate VMAT plans by dynamic rotation of the collimator to align the MLC leaves with the dominant prostate motion direction.MethodsFor 22 prostate cancer patients, two dual arc VMAT plans were made with (1) fixed collimators (45° and 315°) and (2) a rotating collimator that aligned the MLC leaves with the dominant prostate motion direction (population-based first principal component). The fixed and rotating collimator plan quality was compared using selected dose–volume indices. Next, MLC tracking treatments were simulated with 695 patient-measured prostate traces. The MLC exposure error (under- and overexposed MLC area in beam’s eye view) was calculated as a surrogate for the MLC tracking error. Finally, motion including dose reconstruction was performed for 35 motion traces for one patient, and the root-mean-square dose error was compared with the MLC exposure error.ResultsRotating collimator VMAT plans were of similar quality as the fixed collimator plans, but significantly improved MLC tracking with 33% lower MLC exposure errors (p ≪ 0.0001). The reductions in MLC exposure error correlated significantly with dose error reductions.ConclusionProstate VMAT plans with rotating collimator were of similar quality as fixed collimator plans, but more suitable for MLC tracking with significantly better agreement between planned and delivered dose distributions. MLC tracking for prostate cancer patients can therefore be improved without the requirement of additional efforts or hardware changes.