title: The effect of extremely narrow MLC leaf width on the plan quality of VMAT for prostate cancer.
abstract: BACKGROUND
  To investigate the effect of multi-leaf collimators (MLCs) with leaf width of 1.25 mm on the plan quality of volumetric modulated arc therapy (VMAT) for prostate cancer.
  
  
  METHODS
  A total of 20 patients with prostate cancer were retrospectively selected. Using a high definition MLC (HD MLC), primary and boost VMAT plans with two full arcs were generated for each patient (original plan). After that, by shifting the isocenter position of the 2nd arc by 1.25 mm in the cranio-caudal direction, we simulated fluences made with MLCs with leaf width of 1.25 mm. After shifting, primary and boost plans were generated for each patient (shifted plan). A sum plan was generated by summation of the primary and boost plan for each patient. Dose-volumetric parameters were calculated and compared.
  
  
  RESULTS
  Both the homogeneity index (HI) and conformity index (CI) of the shifted plans were better than those of the original plans in primary plans (HI = 0.065 vs. 0.059 with p < 0.001 and CI = 1.056 vs. 1.044 with p = 0.006). Similarly, the shifted plans for the boost target volume showed better homogeneity and conformity than did the original plans (HI = 0.060 vs. 0.053 with p < 0.001 and CI = 1.015 vs. 1.009 with p < 0.001). The target mean dose of the original plans was closer to the prescription dose than that of the shifted plans in the case of sum plans (81.45 Gy vs. 81.12 Gy with p = 0.001).
  
  
  CONCLUSIONS
  Use of extremely narrow MLCs could increase dose homogeneity and conformity of the target volume for prostate VMAT.
authors.affiliation: Department of Radiation Oncology, Seoul National University Hospital, Seoul, South Korea.|Institute of Radiation Medicine, Seoul National University Medical Research Center, Seoul, South Korea.|Biomedical Research Institute, Seoul National University College of Medicine, Seoul, South Korea.|Center for Convergence Research on Robotics, Advanced Institutes of Convergence Technology, Suwon, South Korea.
authors.forename: Jong Min
authors.initials: JM
authors.lastname: Park
authors.affiliation: Department of Radiation Oncology, Seoul National University Hospital, Seoul, South Korea.|Institute of Radiation Medicine, Seoul National University Medical Research Center, Seoul, South Korea.|Biomedical Research Institute, Seoul National University College of Medicine, Seoul, South Korea.|Center for Convergence Research on Robotics, Advanced Institutes of Convergence Technology, Suwon, South Korea.
authors.forename: So-Yeon
authors.initials: SY
authors.lastname: Park
authors.affiliation: Department of Radiation Oncology, Seoul National University Hospital, Seoul, South Korea.|Institute of Radiation Medicine, Seoul National University Medical Research Center, Seoul, South Korea.|Biomedical Research Institute, Seoul National University College of Medicine, Seoul, South Korea.
authors.forename: Jin Ho
authors.initials: JH
authors.lastname: Kim
authors.affiliation: Program in Biomedical Radiation Sciences, Department of Transdisciplinary Studies, Seoul National University Graduate School of Convergence Science and Technology, Seoul, South Korea.
authors.forename: Joel
authors.initials: J
authors.lastname: Carlson
authors.affiliation: Department of Radiation Oncology, Seoul National University Hospital, Seoul, South Korea. madangin@gmail.com.|Institute of Radiation Medicine, Seoul National University Medical Research Center, Seoul, South Korea. madangin@gmail.com.|Biomedical Research Institute, Seoul National University College of Medicine, Seoul, South Korea. madangin@gmail.com.|Center for Convergence Research on Robotics, Advanced Institutes of Convergence Technology, Suwon, South Korea. madangin@gmail.com.
authors.forename: Jung-In
authors.initials: JI
authors.lastname: Kim
mesh_terms: D006801:Humans; D008297:Male; D019047:Phantoms, Imaging; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000295:instrumentation* / Q000379:methods*; D012189:Retrospective Studies
keywords: Leaf width; Multi-leaf collimator; Prostate cancer; Volumetric modulated arc therapy