title: Dosimetric effects of sectional adjustments of collimator angles on volumetric modulated arc therapy for irregularly-shaped targets.
abstract: OBJECTIVE
  To calculate an optimal collimator angle at each of sectional arcs in a full-arc volumetric modulated arc therapy (VMAT) plan and evaluate dosimetric quality of these VMAT plans comparing full-arc VMAT plans with a fixed collimator angle.
  
  
  METHODS
  Seventeen patients who had irregularly-shaped target in abdominal, head and neck, and chest cases were selected retrospectively. To calculate an optimal collimator angle at each of sectional arcs in VMAT, integrated MLC apertures which could cover all shapes of target determined by beam's-eye view (BEV) within angular sections were obtained for each VMAT plan. The angular sections were 40°, 60°, 90° and 120°. When the collimator settings were rotated at intervals of 2°, we obtained the optimal collimator angle to minimize area size difference between the integrated MLC aperture and collimator settings with 5 mm-margins to the integrated MLC aperture. The VMAT plans with the optimal collimator angles (Colli-VMAT) were generated in the EclipseTM. For comparison purposes, one full-arc VMAT plans with a fixed collimator angles (Std-VMAT) were generated. The dose-volumetric parameters and total MUs were evaluated.
  
  
  RESULTS
  The mean dose-volumetric parameters for target volume of Colli-VMAT were comparable to Std-VMAT. Colli-VMAT improved sparing of most normal organs but for brain stem, compared to Std-VMAT for all cases. There were decreasing tendencies in mean total MUs with decreasing angular section. The mean total MUs for Colli-VMAT with the angular section of 40° (434 ± 95 MU, 317 ± 81 MU, and 371 ± 43 MU for abdominal, head and neck, and chest cases, respectively) were lower than those for Std-VMAT (654 ± 182 MU, 517 ± 116 MU, and 533 ± 25 MU, respectively).
  
  
  CONCLUSIONS
  For an irregularly-shaped target, Colli-VMAT with the angular section of 40° reduced total MUs and improved sparing of normal organs, compared to Std-VMAT.
authors.affiliation: Department of Radiation Oncology, Seoul National University Hospital, Seoul, Republic of Korea.
authors.forename: Beom Seok
authors.initials: BS
authors.lastname: Ahn
authors.affiliation: Department of Radiation Oncology, Seoul National University Hospital, Seoul, Republic of Korea.|Biomedical Research Institute, Seoul National University College of Medicine, Seoul, Republic of Korea.|Institute of Radiation Medicine, Seoul National University Medical Research Center, Seoul, Republic of Korea.
authors.forename: So-Yeon
authors.initials: SY
authors.lastname: Park
authors.affiliation: Department of Radiation Oncology, Seoul National University Hospital, Seoul, Republic of Korea.|Biomedical Research Institute, Seoul National University College of Medicine, Seoul, Republic of Korea.|Institute of Radiation Medicine, Seoul National University Medical Research Center, Seoul, Republic of Korea.|Center for Convergence Research on Robotics, Advanced Institutes of Convergence Technology, Suwon, Republic of Korea.
authors.forename: Jong Min
authors.initials: JM
authors.lastname: Park
authors.affiliation: Department of Radiation Oncology, Seoul National University Hospital, Seoul, Republic of Korea.|Biomedical Research Institute, Seoul National University College of Medicine, Seoul, Republic of Korea.|Institute of Radiation Medicine, Seoul National University Medical Research Center, Seoul, Republic of Korea.
authors.forename: Chang Heon
authors.initials: CH
authors.lastname: Choi
authors.affiliation: Department of Radiation Oncology, Seoul National University Hospital, Seoul, Republic of Korea.|Biomedical Research Institute, Seoul National University College of Medicine, Seoul, Republic of Korea.|Institute of Radiation Medicine, Seoul National University Medical Research Center, Seoul, Republic of Korea.
authors.forename: Minsoo
authors.initials: M
authors.lastname: Chun
authors.affiliation: Department of Radiation Oncology, Seoul National University Hospital, Seoul, Republic of Korea.|Biomedical Research Institute, Seoul National University College of Medicine, Seoul, Republic of Korea.|Institute of Radiation Medicine, Seoul National University Medical Research Center, Seoul, Republic of Korea.
authors.forename: Jung-In
authors.initials: JI
authors.lastname: Kim
mesh_terms: D006801:Humans; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation / Q000379:methods*