title: Intensity modulated proton and photon therapy for early prostate cancer with or without transperineal injection of a polyethylen glycol spacer: a treatment planning comparison study.
abstract: OBJECTIVE
  Rectal toxicity is a serious adverse effect in early-stage prostate cancer patients treated with curative radiation therapy (RT). Injecting a spacer between Denonvilliers' fascia increases the distance between the prostate and the anterior rectal wall and may thus decrease the rectal radiation-induced toxicity. We assessed the dosimetric impact of this spacer with advanced delivery RT techniques, including intensity modulated RT (IMRT), volumetric modulated arc therapy (VMAT), and intensity modulated proton beam RT (IMPT).
  
  
  METHODS
  Eight prostate cancer patients were simulated for RT with or without spacer. Plans were computed for IMRT, VMAT, and IMPT using the Eclipse treatment planning system using both computed tomography spacer+ and spacer- data sets. Prostate ± seminal vesicle planning target volume [PTV] and organs at risk (OARs) dose-volume histograms were calculated. The results were analyzed using dose and volume metrics for comparative planning.
  
  
  RESULTS
  Regardless of the radiation technique, spacer injection decreased significantly the rectal dose in the 60- to 70-Gy range. Mean V(70 Gy) and V(60 Gy) with IMRT, VMAT, and IMPT planning were 5.3 ± 3.3%/13.9 ± 10.0%, 3.9 ± 3.2%/9.7 ± 5.7%, and 5.0 ± 3.5%/9.5 ± 4.7% after spacer injection. Before spacer administration, the corresponding values were 9.8 ± 5.4% (P=.012)/24.8 ± 7.8% (P=.012), 10.1 ± 3.0% (P=.002)/17.9 ± 3.9% (P=.003), and 9.7 ± 2.6% (P=.003)/14.7% ± 2.7% (P=.003). Importantly, spacer injection usually improved the PTV coverage for IMRT. With this technique, mean V(70.2 Gy) (P=.07) and V(74.1 Gy) (P=0.03) were 100 ± 0% to 99.8 ± 0.2% and 99.1 ± 1.2% to 95.8 ± 4.6% with and without Spacer, respectively. As a result of spacer injection, bladder doses were usually higher but not significantly so. Only IMPT managed to decrease the rectal dose after spacer injection for all dose levels, generally with no observed increase to the bladder dose.
  
  
  CONCLUSIONS
  Regardless of the radiation technique, a substantial decrease of rectal dose was observed after spacer injection for curative RT to the prostate.
authors.affiliation: Department of Radiation Oncology, Geneva University Hospital, Geneva, Switzerland. damien.weber@unige.ch
authors.forename: Damien C
authors.initials: DC
authors.lastname: Weber
authors.forename: Thomas
authors.initials: T
authors.lastname: Zilli
authors.forename: Jean Paul
authors.initials: JP
authors.lastname: Vallee
authors.forename: Michel
authors.initials: M
authors.lastname: Rouzaud
authors.forename: Raymond
authors.initials: R
authors.lastname: Miralbell
authors.forename: Luca
authors.initials: L
authors.lastname: Cozzi
mesh_terms: D020341:Absorbable Implants; D000368:Aged; D006801:Humans; D008297:Male; D008875:Middle Aged; D017785:Photons / Q000627:therapeutic use*; D011092:Polyethylene Glycols / Q000008:administration & dosage*; D011467:Prostate / Q000000981:diagnostic imaging; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy*; D061766:Proton Therapy; D011832:Radiation Injuries / Q000517:prevention & control*; D011859:Radiography; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D012007:Rectum / Q000000981:diagnostic imaging / Q000528:radiation effects*; D001743:Urinary Bladder / Q000000981:diagnostic imaging / Q000528:radiation effects
chemical_list: D011092:Polyethylene Glycols