title: Role of image guided radiation therapy in obese patients with gynecologic malignancies.
abstract: OBJECTIVE
  We investigated the effect of body mass index on setup errors by analyzing daily shifts required in treating patients undergoing image guided radiation therapy (IGRT) for gynecologic malignancies.
  
  
  METHODS
  Forty successive patients treated with daily kV-based IGRT for gynecologic malignancies between April 2009 and June 2012 were identified. Directional setup corrections were analyzed according to patient body mass index. Random and systematic setup errors were calculated. Image acquisition dose was estimated by performing ionization chamber measurements in a phantom.
  
  
  RESULTS
  Obese patients had larger random setup errors, particularly in the right-left (R-L) direction, with a setup error of 7.6 mm, versus 3.9 mm for nonobese patients. The range of individual patient random errors in the R-L direction was 1.5 to 7.6 mm among nonobese patients versus 2.0 to 17.0 mm among obese patients (P = .03, F-test). For obese patients, daily IGRT prevented treating outside the planning target volume in 33% of fractions, versus 16% in the nonobese group (P = .001). The mean total image acquisition dose from daily kV-IGRT was approximately 3 cGy, versus 150 cGy if daily megavoltage portal imaging were used to correct for erratic setup errors.
  
  
  CONCLUSIONS
  Daily kV-based IGRT in obese patients allows for correction of erratic setup error and minimizes excess dose from portal imaging.
authors.affiliation: Department of Radiation Oncology, Loyola University Medical Center, Maywood, Illinois. Electronic address: tbray@lumc.edu.
authors.forename: Tracy S
authors.initials: TS
authors.lastname: Bray
authors.affiliation: Department of Radiation Oncology, Loyola University Medical Center, Maywood, Illinois.
authors.forename: Adelaide
authors.initials: A
authors.lastname: Kaczynski
authors.affiliation: Department of Radiation Oncology, Loyola University Medical Center, Maywood, Illinois.
authors.forename: Kevin
authors.initials: K
authors.lastname: Albuquerque
authors.affiliation: Department of Radiation Oncology, Loyola University Medical Center, Maywood, Illinois.
authors.forename: Francesca
authors.initials: F
authors.lastname: Cozzi
authors.affiliation: Department of Radiation Oncology, Loyola University Medical Center, Maywood, Illinois.
authors.forename: John C
authors.initials: JC
authors.lastname: Roeske