title: The impact of stool and gas volume on intrafraction prostate motion in patients undergoing radiotherapy with daily endorectal balloon.
abstract: OBJECTIVE
  The aim of this study was to quantify the impact of rectal stool/gas volumes on intrafraction prostate motion for patients undergoing prostate radiotherapy with daily endorectal balloon (ERB).
  
  
  METHODS
  Total and anterior stool/gas rectal volumes were quantified in 30 patients treated with daily ERB. Real-time intrafraction prostate motion from 494 treatment sessions, at most 6 min in length, was evaluated using Calypso(®) tracking system.
  
  
  RESULTS
  The deviation of prostate intrafraction motion distribution was a function of stool/gas volume, especially when stool/gas is located in the anterior part of the rectum. Compared to patients with small anterior stool/gas volumes (<10 cm(3)), those with large volume (10-60 cm(3)) had a twofold increase in 3D prostate motion and interquartile data range within the 6th minute of treatment time. The 10% of the overall CBCT session where large anterior rectal volumes were observed demonstrated larger percentage of time at displacement greater than our proposed internal margin 3 mm.
  
  
  CONCLUSIONS
  Volume and location of stool/gas can directly impact the ERB's intrafraction immobilization ability. Although our patient preparation protocol and the 100 cm(3) daily ERB effectively stabilized prostate motion for 90% of the fractions, a larger-sized ERB may improve prostate fixation for patients with greater and/or variable daily rectal volume.
authors.affiliation: Department of Radiation Oncology, University of Pennsylvania, Philadelphia; Department of Radiation Oncology and Molecular Radiation Sciences, Johns Hopkins University, Baltimore. Electronic address: kwang27@jhmi.edu.
authors.forename: Ken Kang-Hsin
authors.initials: KK
authors.lastname: Wang
authors.affiliation: Department of Radiation Oncology, University of Pennsylvania, Philadelphia.
authors.forename: Neha
authors.initials: N
authors.lastname: Vapiwala
authors.affiliation: Department of Radiation Oncology, University of Pennsylvania, Philadelphia.
authors.forename: Viet
authors.initials: V
authors.lastname: Bui
authors.affiliation: Department of Radiation Oncology, University of Pennsylvania, Philadelphia.
authors.forename: Curtiland
authors.initials: C
authors.lastname: Deville
authors.affiliation: Department of Radiation Oncology, University of Pennsylvania, Philadelphia.
authors.forename: John P
authors.initials: JP
authors.lastname: Plastaras
authors.affiliation: Department of Radiation Oncology, Thomas Jefferson University, Philadelphia, USA.
authors.forename: Voichita
authors.initials: V
authors.lastname: Bar-Ad
authors.affiliation: Department of Radiation Oncology, University of Pennsylvania, Philadelphia.
authors.forename: Zelig
authors.initials: Z
authors.lastname: Tochner
authors.affiliation: Department of Radiation Oncology, University of Pennsylvania, Philadelphia.
authors.forename: Stefan
authors.initials: S
authors.lastname: Both
mesh_terms: D000230:Adenocarcinoma / Q000532:radiotherapy*; D054893:Cone-Beam Computed Tomography; D005243:Feces; D005414:Flatulence; D006801:Humans; D008297:Male; D009068:Movement; D056888:Patient Positioning; D011446:Prospective Studies; D011467:Prostate / Q000000981:diagnostic imaging*; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D012007:Rectum
keywords: Endorectal balloon; Intrafraction motion; Prostate; Rectal filling