title: Impact of planning target volume margins and rectal distention on biochemical failure in image-guided radiotherapy of prostate cancer.
abstract: OBJECTIVE
  A previous study in our department demonstrated the negative impact on freedom from biochemical failure (FFBF) of using too narrow planning target volume (PTV) margins during prostate image-guided radiotherapy (IGRT). Here, we investigated the impact of appropriate PTV margins and rectal distention on FFBF.
  
  
  METHODS
  A total of 50 T1-T3N0M0 prostate cancer patients were treated with daily IGRT by implanted markers. In the first 25 patients, PTV margins were 3mm laterolateral, 5mm anterioposterior and 4mm craniocaudal. The subsequent 25 patients were treated with isotropic margins of 6mm. The rectal cross-sectional area (CSA) was determined on the planning CT. Median follow-up was 61months.
  
  
  RESULTS
  The overall 5-year FFBF was 83%. A 6mm PTV margin was related to increased 5-year FFBF on univariate analysis (96% vs 74% with the tighter PTV margins, p=0.04). The 5-year FFBF of patients with a rectal distention on the planning CT was worse compared to those with limited rectal filling (75% for CSA⩾9cm(2) vs 89% for CSA<9cm(2), p=0.02), which remained significant on multivariate analysis (p=0.04).
  
  
  CONCLUSIONS
  This retrospective study illustrated the positive impact of PTV margin adaptation and addressed the importance of avoiding rectal distention at time of the planning CT.
authors.affiliation: Department of Radiotherapy, UZ Brussel, Vrije Universiteit Brussel, Belgium. Electronic address: benedikt.engels@gmail.com.
authors.forename: Benedikt
authors.initials: B
authors.lastname: Engels
authors.affiliation: Department of Radiotherapy, UZ Brussel, Vrije Universiteit Brussel, Belgium.
authors.forename: Guy
authors.initials: G
authors.lastname: Soete
authors.affiliation: Department of Radiotherapy, UZ Brussel, Vrije Universiteit Brussel, Belgium.
authors.forename: Thierry
authors.initials: T
authors.lastname: Gevaert
authors.affiliation: Department of Radiotherapy, UZ Brussel, Vrije Universiteit Brussel, Belgium.
authors.forename: Guy
authors.initials: G
authors.lastname: Storme
authors.affiliation: Department of Urology, UZ Brussel, Vrije Universiteit Brussel, Belgium.
authors.forename: Dirk
authors.initials: D
authors.lastname: Michielsen
authors.affiliation: Department of Radiotherapy, UZ Brussel, Vrije Universiteit Brussel, Belgium.
authors.forename: Mark
authors.initials: M
authors.lastname: De Ridder
mesh_terms: D000368:Aged; D015331:Cohort Studies; D018572:Disease-Free Survival; D006801:Humans; D008297:Male; D008875:Middle Aged; D009367:Neoplasm Staging; D011471:Prostatic Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D061089:Radiotherapy, Image-Guided / Q000379:methods; D012007:Rectum / Q000033:anatomy & histology / Q000528:radiation effects; D012189:Retrospective Studies; D017211:Treatment Failure
keywords: Biochemical failure; Image-guided radiotherapy; Prostate cancer; Rectal distention