title: Comparison of hybrid volumetric modulated arc therapy (VMAT) technique and double arc VMAT technique in the treatment of prostate cancer.
abstract: BACKGROUND
  Volumetric modulated arc therapy (VMAT) has quickly become accepted as standard of care for the treatment of prostate cancer based on studies showing it is able to provide faster delivery with adequate target coverage and reduced monitor units while maintaining organ at risk (OAR) sparing. This study aims to demonstrate the potential to increase dose conformality with increased planner control and OAR sparing using a hybrid treatment technique compared to VMAT.
  
  
  METHODS
  Eleven patients having been previously treated for prostate cancer with VMAT techniques were replanned with a hybrid technique on Varian Treatment Planning System. Multiple static IMRT fields (2 to 3) were planned initially based on critical OAR to reduce dose but provide some planning treatment volume (PTV) coverage. This was used as a base dose plan to provide 30-35% coverage for a single arc VMAT plan.
  
  
  RESULTS
  The clinical VMAT plan was used as a control for the purposes of comparison. Average of all OAR sparing between the hybrid technique and VMAT showed the hybrid plan delivering less dose in almost all cases except for V80 of the bladder and maximum dose to right femoral head. PTV coverage was superior with the VMAT technique. Monitor unit differences varied, with the hybrid plan able to deliver fewer units 37% of the time, similar results 18% of the time, and higher units 45% of the time. On average, the hybrid plan delivered 10% more monitor units.
  
  
  CONCLUSIONS
  The hybrid plan can be delivered in a single gantry rotation combining aspects of VMAT with regions of dynamic intensity modulated radiation therapy (IMRT) within the treatment arc.
authors.affiliation: Department of Radiation Medicine, Roswell Park Cancer Institute, Buffalo, NY, USA.
authors.forename: Christopher
authors.initials: C
authors.lastname: Amaloo
authors.affiliation: Department of Radiation Medicine, Roswell Park Cancer Institute and Department of Biophysics and Physiology, University at Buffalo, Buffalo, USA.
authors.forename: Daryl P
authors.initials: DP
authors.lastname: Nazareth
authors.affiliation: Department of Radiation Medicine and Department of Cell Stress Biology, Roswell Park Cancer Institute, Buffalo, USA.
authors.forename: Lalith K
authors.initials: LK
authors.lastname: Kumaraswamy
keywords: VMAT; hybrid; planning; prostate