Plan complexity quantification of dual-layer multi-leaf collimator for volumetric modulated arc therapy with Halcyon lin
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SCIENTIFIC PAPER
Plan complexity quantification of dual-layer multi-leaf collimator for volumetric modulated arc therapy with Halcyon linac Mikoto Tamura1 · Kenji Matsumoto2 · Masakazu Otsuka1,2 · Hajime Monzen1 Received: 13 December 2019 / Accepted: 23 June 2020 © Australasian College of Physical Scientists and Engineers in Medicine 2020
Abstract This study characterized the plan complexity of the dual-layer multi-leaf collimator (MLC) performance for volumetric modulated arc therapy (VMAT) in Halcyon. Plan complexity metrics were computed independently for each MLC layer (proximal and distal): modulation complexity score (MCS), plan averaged beam area, irregularity, and modulation (PA, PI, and PM) were obtained. These were investigated when weighted by proportions of the effective proximal MLC and distal MLC (MCSw, PAw, PIw, and P Mw). Conventional plan complexity metrics for the effective 5.0 mm resolution MLC ( MCS5, PA5, PI5, PM5), small aperture score (SAS), effective distal MLC score (EDS), and MU were also evaluated. Forty-five consecutive VMAT plans were analyzed retrospectively for treatment sites of the prostate, head and neck (HN), and other parts. The mean values of the metrics for proximal MLC and distal MLC were 0.310 and 0.245 (MCS), 71.09 cm2 and 55.92 cm2 (PA), 6.24 and 10.19 (PI), and 0.593 and 0.645 (PM), respectively. The degree of plan complexity in the distal MLC was larger than in the proximal MLC. The percentage of the effective distal MLC was higher than that of the proximal MLC (mean EDS = 0.555). The MCSw, PAw, PIw, and PMw showed significant differences between the prostate and HN groups like the PA5, PI5, and PM5; however, the MCS5 did not. Additionally, the MCS5 correlated with MU and PM5, while the MCSw correlated with SAS and PA5. The plan complexity for each MLC layer and subsequently combining these complexities might be useful to better understand the dual-layer MLC performance. Keywords Plan complexity · Dual-layer MLC · Halcyon · VMAT
Introduction High precision radiotherapy, intensity modulated radiotherapy (IMRT), volumetric modulated arc therapy (VMAT), and stereotactic radiotherapy improve both target conformity and normal tissue sparing, which results in reduced acute and late toxicities; in contrast, the plan complexity (e.g., the beam modulation, the total number of monitor units (MUs), and the dosimetric uncertainty) is increased when compared with that of conventional radiotherapy [1, 2]. Evaluations of both the plan complexity and the dosimetric accuracy are thus required as part of the pre-treatment quality assurance * Hajime Monzen [email protected] 1
Department of Medical Physics, Graduate School of Medical Sciences, Kindai University, 377‑2 Onohigashi, Osakasayama, Osaka 5898511, Japan
Department of Radiology, Kindai University Hospital, 377‑2 Onohigashi, Osakasayama, Osaka 5898511, Japan
2
(QA) in AAPM TG-218 [3]. Characterization of the plan complexity for each treatment site is useful for VMAT plan evaluation before vali
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