title: Dosimetric effects of multileaf collimator leaf width on intensity-modulated radiotherapy for head and neck cancer.
abstract: OBJECTIVE
  The authors evaluated the effects of multileaf collimator (MLC) leaf width (2.5 vs. 5 mm) on dosimetric parameters and delivery efficiencies of intensity-modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT) for head and neck (H&N) cancers.
  
  
  METHODS
  The authors employed two types of mock phantoms: large-sized head and neck (LH&N) and small-sized C-shape (C-shape) phantoms. Step-and-shoot IMRT (S&S_IMRT) and VMAT treatment plans were designed with 2.5- and 5.0-mm MLC for both C-shape and LH&N phantoms. Their dosimetric characteristics were compared in terms of the conformity index (CI) and homogeneity index (HI) for the planning target volume (PTV), the dose to organs at risk (OARs), and the dose-spillage volume. To analyze the effects of the field and arc numbers, 9-field IMRT (9F-IMRT) and 13-field IMRT (13F-IMRT) plans were established for S&S_IMRT. For VMAT, single arc (VMAT1) and double arc (VMAT2) plans were established. For all plans, dosimetric verification was performed using the phantom to examine the relationship between dosimetric errors and the two leaf widths. Delivery efficiency of the two MLCs was compared in terms of beam delivery times, monitor units (MUs) per fraction, and the number of segments for each plan.
  
  
  RESULTS
  2.5-mm MLC showed better dosimetric characteristics in S&S_IMRT and VMAT for C-shape, providing better CI for PTV and lower spinal cord dose and high and intermediate dose-spillage volume as compared with the 5-mm MLC (p < 0.05). However, no significant dosimetric benefits were provided by the 2.5-mm MLC for LH&N (p > 0.05). Further, beam delivery efficiency was not observed to be significantly associated with leaf width for either C-shape or LH&N. However, MUs per fraction were significantly reduced for the 2.5-mm MLC for the LH&N. In dosimetric error analysis, absolute dose evaluations had errors of less than 3%, while the Gamma passing rate was greater than 95% according to the 3%/3 mm criteria. There were no significant differences in dosimetric error between the 2.5- and 5-mm MLCs.
  
  
  CONCLUSIONS
  As compared with MLC of 5-mm leaf widths, MLC with finer leaf width (2.5-mm) can provide better dosimetric outcomes in IMRT for C-shape. However, the MLC leaf width may only have minor effects on dosimetric characteristics in IMRT for LH&N. The results of the present study will serve as a useful assessment standard when assigning or introducing equipment for the treatment of H&N cancers.
authors: Department of Radiation Oncology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul 135-710, South Korea.
authors: Chae-Seon
authors: CS
authors: Hong
authors: Department of Radiation Oncology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul 135-710, South Korea.
authors: Sang Gyu
authors: SG
authors: Ju
authors: Department of Radiation Oncology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul 135-710, South Korea.
authors: Minkyu
authors: M
authors: Kim
authors: Department of Radiation Oncology, Kangbuk Samsung Hospital, Sungkyunkwhan University School of Medicine, Seoul 110-746, South Korea.
authors: Jung-In
authors: JI
authors: Kim
authors: Department of Radiation Oncology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul 135-710, South Korea.
authors: Jin Man
authors: JM
authors: Kim
authors: Department of Biomedical Engineering and Research Institute of Biomedical Engineering, The Catholic University of Korea, Seoul 137-701, South Korea.
authors: Tae-Suk
authors: TS
authors: Suh
authors: Department of Radiation Oncology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul 135-710, South Korea.
authors: Youngyih
authors: Y
authors: Han
authors: Department of Radiation Oncology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul 135-710, South Korea.
authors: Yong Chan
authors: YC
authors: Ahn
authors: Department of Radiation Oncology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul 135-710, South Korea.
authors: Doo Ho
authors: DH
authors: Choi
authors: Department of Radiation Oncology, Kangbuk Samsung Hospital, Sungkyunkwhan University School of Medicine, Seoul 110-746, South Korea.
authors: Heerim
authors: H
authors: Nam
authors: Department of Radiation Oncology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul 135-710, South Korea.
authors: Hee Chul
authors: HC
authors: Park
mesh_terms: D006258:Head and Neck Neoplasms / Q000532:radiotherapy*; D006801:Humans; D019047:Phantoms, Imaging; D011874:Radiometry; D011880:Radiotherapy Planning, Computer-Assisted; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*