title: On-line correction of beam portals in the treatment of prostate cancer using an endorectal balloon device.
abstract: BACKGROUND
  Reproducible target volume assessment is required in order to optimize portal field margins in the treatment of prostate cancer. The benefits of an endorectal balloon on target volume assessment remain unclear.
  
  
  METHODS
  Nine patients were treated with a daily placed air filled rectal balloon. Portal films and computer-associated tomography during the treatment were used to determine the position of the structures of interest. Comparative planning with or without a balloon was performed in order to determine rectal wall exposure to radiation.
  
  
  RESULTS
  The range of movements during treatment predicting the position of the prostate in relation to the symphysis was 0.05-0.59 cm in the lateral direction, 0.27-2.2 cm in the antero-posterior direction, and 0.33-1.8 cm in the crano-caudal direction, as compared to the position of the prostate predicted by the balloon ranging from 0.18 to 0.76 cm in the lateral direction, 0.22-1.68 cm in the antero-posterior direction, and 0.58-2.99 cm in the crano-caudal direction. Planning target volumes (PTV) margins as defined by the position of the balloon were 10 mm in the antero-posterior direction, 6 mm in the lateral direction, and 16 mm in the crano-caudal direction. The volume of rectal wall exposed to radiation was reduced from 40 (+/- 12%) to 25% (+/- 19%) with an endorectal balloon (P < 0.05).
  
  
  CONCLUSIONS
  Daily online correction with portal vision for external beam set-up is improved by an endorectal balloon device, leading to improved PTV margins and reduced radiation exposure of the rectal wall.
authors.affiliation: Department for Radiation Oncology, University Hospital Zurich, Rämistrasse 100, 8091 Zurich, Switzerland.
authors.forename: Ilja F
authors.initials: IF
authors.lastname: Ciernik
authors.forename: Brigitta G
authors.initials: BG
authors.lastname: Baumert
authors.forename: Peter
authors.initials: P
authors.lastname: Egli
authors.forename: Christoph
authors.initials: C
authors.lastname: Glanzmann
authors.forename: Urs M
authors.initials: UM
authors.lastname: Lütolf
mesh_terms: D000230:Adenocarcinoma / Q000532:radiotherapy*; D000368:Aged; D004307:Dose-Response Relationship, Radiation; D006801:Humans; D008297:Male; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D020266:Radiotherapy, Conformal / Q000295:instrumentation*