title: Intensity-Modulated Radiation Therapy Versus 3D Conformal Radiotherapy for Postoperative Gynecologic Cancer: Are They Covering the Same Planning Target Volume?
abstract: OBJECTIVE
  This study compares dosimetric parameters of planning target volume (PTV) coverage and organs at risk (OAR) sparing when postoperative radiotherapy for gynecologic cancers is delivered using volumetric modulated arc therapy (VMAT) versus a four-field (4FLD) box technique.
  
  
  METHODS
  From July to December 2012, women requiring postoperative radiation for gynecologic cancers were treated with a standardized VMAT protocol. Two sets of optimized 4FLD plans were retrospectively generated: one based on standard anatomical borders (4FLD) and one based on the clinical target volume (CTV) created for VMAT with a 2 cm expansion guiding field border placement (4FLD+2). Ninety-five percent isodose curves were generated to evaluate PTV coverage.
  
  
  RESULTS
  VMAT significantly improved dose conformity compared with 4FLD and 4FLD+2 plans (p < 0.001) and provided additional coverage of the PTV posteriorly and superiorly, corresponding to coverage of the presacral and proximal iliac vessels. There was a significant reduction in dose to all OARs with VMAT, including a 58% reduction in the volume of the small bowel receiving more than 45 Gy (p=0.005).
  
  
  CONCLUSIONS
  Despite treating a larger volume, radiotherapy using a 4FLD technique is less homogenous and provides inferior coverage of the PTV compared with VMAT. With meticulous treatment planning and delivery, VMAT effectively encompasses the PTV and minimizes dose to OARs.
authors.affiliation: Department of Radiation Oncology, London Regional Cancer Program, London, Ontario, CA ; Schulich School of Medicine & Dentistry, Western University, London, Ontario, CA.
authors.forename: Jelena
authors.initials: J
authors.lastname: Lukovic
authors.affiliation: Nova Scotia Cancer Centre, Nova Scotia Health Authority, Dalhousie University.
authors.forename: Nikhilesh
authors.initials: N
authors.lastname: Patil
authors.affiliation: Department of Radiation Oncology, London Regional Cancer Program, London, Ontario, CA ; Schulich School of Medicine & Dentistry, Western University, London, Ontario, CA.
authors.forename: David
authors.initials: D
authors.lastname: D'souza
authors.affiliation: Department of Physics and Engineering, London Health Sciences Center, London, Ontario, CA.
authors.forename: Barbara
authors.initials: B
authors.lastname: Millman
authors.affiliation: Department of Radiation Oncology, London Regional Cancer Program, London, Ontario, CA ; Schulich School of Medicine & Dentistry, Western University, London, Ontario, CA.
authors.forename: Brian P
authors.initials: BP
authors.lastname: Yaremko
authors.affiliation: Toronto Sunnybrook Hospital, University of Toronto.
authors.forename: Eric
authors.initials: E
authors.lastname: Leung
authors.affiliation: Clinical Research Unit, London Health Sciences Center, London, Ontario, Canada.
authors.forename: Frances
authors.initials: F
authors.lastname: Whiston
authors.affiliation: Department of Physics and Engineering, London Health Sciences Center, London, Ontario, CA.
authors.forename: George
authors.initials: G
authors.lastname: Hajdok
authors.affiliation: Division of Radiation Oncology, London Regional Cancer Program, London, Ontario, CA.
authors.forename: Eugene
authors.initials: E
authors.lastname: Wong
keywords: cervix cancer; dosimetry; endometrial cancer; gynecological cancers; intensity-modulated radiotherapy (imrt)