title: Independent absorbed-dose calculation using the Monte Carlo algorithm in volumetric modulated arc therapy.
abstract: OBJECTIVE
  To 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
  All 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-cm2 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.
  
  
  RESULTS
  In 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.
  
  
  CONCLUSIONS
  There 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.
authors.affiliation: Department of Radiology, The University of Tokyo Hospital, Tokyo, Japan. haga-haga@umin.ac.jp.
authors.forename: Akihiro
authors.initials: A
authors.lastname: Haga
authors.forename: Taiki
authors.initials: T
authors.lastname: Magome
authors.forename: Shigeharu
authors.initials: S
authors.lastname: Takenaka
authors.forename: Toshikazu
authors.initials: T
authors.lastname: Imae
authors.forename: Akira
authors.initials: A
authors.lastname: Sakumi
authors.forename: Akihiro
authors.initials: A
authors.lastname: Nomoto
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Igaki
authors.forename: Kenshiro
authors.initials: K
authors.lastname: Shiraishi
authors.forename: Hideomi
authors.initials: H
authors.lastname: Yamashita
authors.forename: Kuni
authors.initials: K
authors.lastname: Ohtomo
authors.forename: Keiichi
authors.initials: K
authors.lastname: Nakagawa
mesh_terms: D000465:Algorithms; D006258:Head and Neck Neoplasms / Q000473:pathology / Q000532:radiotherapy; D006801:Humans; D007414:Intestinal Neoplasms / Q000473:pathology / Q000532:radiotherapy; D008175:Lung Neoplasms / Q000473:pathology / Q000532:radiotherapy; D008297:Male; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D011471:Prostatic Neoplasms / Q000473:pathology / Q000532:radiotherapy; D011874:Radiometry / Q000295:instrumentation / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation / Q000379:methods; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D012189:Retrospective Studies; D054928:Validation Studies as Topic