Independent absorbed-dose calculation using the Monte Carlo algorithm in volumetric modulated arc therapyReport as inadecuate

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Radiation Oncology

, 9:75

Radiation Physics


PurposeTo report the result of independent absorbed-dose calculations based on a Monte Carlo MC algorithm in volumetric modulated arc therapy VMAT for various treatment sites.

Methods and materialsAll treatment plans were created by the superposition-convolution SC algorithm of SmartArc Pinnacle V9.2, Philips. The beam information was converted into the format of the Monaco V3.3 Elekta, which uses the X-ray voxel-based MC XVMC algorithm. The dose distribution was independently recalculated in the Monaco. The dose for the planning target volume PTV and the organ at risk OAR were analyzed via comparisons with those of the treatment plan.

Before performing an independent absorbed-dose calculation, the validation was conducted via irradiation from 3 different gantry angles with a 10- × 10-cm field. For the independent absorbed-dose calculation, 15 patients with cancer prostate, 5; lung, 5; head and neck, 3; rectal, 1; and esophageal, 1 who were treated with single-arc VMAT were selected. To classify the cause of the dose difference between the Pinnacle and Monaco TPSs, their calculations were also compared with the measurement data.

ResultIn validation, the dose in Pinnacle agreed with that in Monaco within 1.5%. The agreement in VMAT calculations between Pinnacle and Monaco using phantoms was exceptional; at the isocenter, the difference was less than 1.5% for all the patients. For independent absorbed-dose calculations, the agreement was also extremely good. For the mean dose for the PTV in particular, the agreement was within 2.0% in all the patients; specifically, no large difference was observed for high-dose regions. Conversely, a significant difference was observed in the mean dose for the OAR. For patients with prostate cancer, the mean rectal dose calculated in Monaco was significantly smaller than that calculated in Pinnacle.

ConclusionsThere was no remarkable difference between the SC and XVMC calculations in the high-dose regions. The difference observed in the low-dose regions may have arisen from various causes such as the intrinsic dose deviation in the MC calculation, modeling accuracy, and CT-to-density table used in each planning system It is useful to perform independent absorbed-dose calculations with the MC algorithm in intensity-modulated radiation therapy commissioning.

Electronic supplementary materialThe online version of this article doi:10.1186-1748-717X-9-75 contains supplementary material, which is available to authorized users.

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Author: Akihiro Haga - Taiki Magome - Shigeharu Takenaka - Toshikazu Imae - Akira Sakumi - Akihiro Nomoto - Hiroshi Igaki - Kenshir


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