title: Reduction of prostate intrafraction motion using gas-release rectal balloons.
abstract: OBJECTIVE
  To analyze prostate intrafraction motion using both non-gas-release (NGR) and gas-release (GR) rectal balloons and to evaluate the ability of GR rectal balloons to reduce prostate intrafraction motion.
  
  
  METHODS
  Twenty-nine patients with NGR rectal balloons and 29 patients with GR balloons were randomly selected from prostate patients treated with proton therapy at the University of Florida Proton Therapy Institute (Jacksonville, FL). Their pretreatment and post-treatment orthogonal radiographs were analyzed, and both pretreatment setup residual error and intrafraction-motion data were obtained. Population histograms of intrafraction motion were plotted for both types of balloons. Population planning target-volume (PTV) margins were calculated with the van Herk formula of 2.5Σ + 0.7σ to account for setup residual errors and intrafraction motion errors.
  
  
  RESULTS
  Pretreatment and post-treatment radiographs indicated that the use of gas-release rectal balloons reduced prostate intrafraction motion along superior-inferior (SI) and anterior-posterior (AP) directions. Similar patient setup residual errors were exhibited for both types of balloons. Gas-release rectal balloons resulted in PTV margin reductions from 3.9 to 2.8 mm in the SI direction, 3.1 to 1.8 mm in the AP direction, and an increase from 1.9 to 2.1 mm in the left-right direction.
  
  
  CONCLUSIONS
  Prostate intrafraction motion is an important uncertainty source in radiotherapy after image-guided patient setup with online corrections. Compared to non-gas-release rectal balloons, gas-release balloons can reduce prostate intrafraction motion in the SI and AP directions caused by gas buildup.
authors.affiliation: Department of Radiation Oncology, University of Florida Proton Therapy Institute, Jacksonville, FL, USA. zsu@floridaproton.org
authors.forename: Zhong
authors.initials: Z
authors.lastname: Su
authors.forename: Tianyu
authors.initials: T
authors.lastname: Zhao
authors.forename: Zuofeng
authors.initials: Z
authors.lastname: Li
authors.forename: Brad
authors.initials: B
authors.lastname: Hoppe
authors.forename: Randy
authors.initials: R
authors.lastname: Henderson
authors.forename: William
authors.initials: W
authors.lastname: Mendenhall
authors.forename: R Charles
authors.initials: RC
authors.lastname: Nichols
authors.forename: Robert
authors.initials: R
authors.lastname: Marcus
authors.forename: Nancy
authors.initials: N
authors.lastname: Mendenhall
mesh_terms: D019583:Dose Fractionation, Radiation; D005740:Gases / Q000378:metabolism*; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism; D008297:Male; D009068:Movement; D011467:Prostate / Q000503:physiopathology*; D011471:Prostatic Neoplasms / Q000378:metabolism / Q000503:physiopathology / Q000532:radiotherapy*; D011878:Radiotherapy / Q000295:instrumentation / Q000379:methods*; D012007:Rectum
chemical_list: D005740:Gases