title: Improving Delivery Accuracy of Stereotactic Body Radiotherapy to a Moving Tumor Using Simplified Volumetric Modulated Arc Therapy.
abstract: OBJECTIVE
  To develop a simplified volumetric modulated arc therapy (VMAT) technique for more accurate dose delivery in thoracic stereotactic body radiation therapy (SBRT).
  
  
  METHODS
  For each of the 22 lung SBRT cases treated with respiratory-gated VMAT, a dose rate modulated arc therapy (DrMAT) plan was retrospectively generated. A dynamic conformal arc therapy plan with 33 adjoining coplanar arcs was designed and their beam weights were optimized by an inverse planning process. All sub-arc beams were converted into a series of control points with varying MLC segment and dose rates and merged into an arc beam for a DrMAT plan. The plan quality of original VMAT and DrMAT was compared in terms of target coverage, compactness of dose distribution, and dose sparing of organs at risk. To assess the delivery accuracy, the VMAT and DrMAT plans were delivered to a motion phantom programmed with the corresponding patients' respiratory signal; results were compared using film dosimetry with gamma analysis.
  
  
  RESULTS
  The plan quality of DrMAT was equivalent to that of VMAT in terms of target coverage, dose compactness, and dose sparing for the normal lung. In dose sparing for other critical organs, DrMAT was less effective than VMAT for the spinal cord, heart, and esophagus while being well within the limits specified by the Radiation Therapy Oncology Group. Delivery accuracy of DrMAT to a moving target was similar to that of VMAT using a gamma criterion of 2%/2mm but was significantly better using a 2%/1mm criterion, implying the superiority of DrMAT over VMAT in SBRT for thoracic/abdominal tumors with respiratory movement.
  
  
  CONCLUSIONS
  We developed a DrMAT technique for SBRT that produces plans of a quality similar to that achieved with VMAT but with better delivery accuracy. This technique is well-suited for small tumors with motion uncertainty.
authors.affiliation: Department of Radiation Oncology, Ulsan University Hospital, Ulsan, Korea.
authors.forename: Young Eun
authors.initials: YE
authors.lastname: Ko
authors.affiliation: Department of Radiation Oncology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea.
authors.forename: Byungchul
authors.initials: B
authors.lastname: Cho
authors.affiliation: Department of Radiation Oncology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea.
authors.forename: Su Ssan
authors.initials: SS
authors.lastname: Kim
authors.affiliation: Department of Radiation Oncology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea.
authors.forename: Si Yeol
authors.initials: SY
authors.lastname: Song
authors.affiliation: Department of Radiation Oncology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea.
authors.forename: Eun Kyung
authors.initials: EK
authors.lastname: Choi
authors.affiliation: Department of Radiation Oncology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea.
authors.forename: Seung Do
authors.initials: SD
authors.lastname: Ahn
authors.affiliation: Department of Radiation Oncology, University of Maryland School of Medicine, Baltimore, Maryland, United States of America.
authors.forename: Byongyong
authors.initials: B
authors.lastname: Yi
mesh_terms: D004307:Dose-Response Relationship, Radiation; D006801:Humans; D008175:Lung Neoplasms / Q000532:radiotherapy*; D011874:Radiometry; D016634:Radiosurgery; D050397:Radiotherapy, Intensity-Modulated