title: Is a 3-mm intrafractional margin sufficient for daily image-guided intensity-modulated radiation therapy of prostate cancer?
abstract: OBJECTIVE
  To determine whether a 3-mm isotropic target margin adequately covers the prostate and seminal vesicles (SVs) during administration of an intensity-modulated radiation therapy (IMRT) treatment fraction, assuming that daily image-guided setup is performed just before each fraction.
  
  
  METHODS
  In-room computed tomographic (CT) scans were acquired immediately before and after a daily treatment fraction in 46 patients with prostate cancer. An eight-field IMRT plan was designed using the pre-fraction CT with a 3-mm margin and subsequently recalculated on the post-fraction CT. For convenience of comparison, dose plans were scaled to full course of treatment (75.6 Gy). Dose coverage was assessed on the post-treatment CT image set.
  
  
  RESULTS
  During one treatment fraction (21.4+/-5.5 min), there were reductions in the volumes of the prostate and SVs receiving the prescribed dose (median reduction 0.1% and 1.0%, respectively, p<0.001) and in the minimum dose to 0.1 cm(3) of their volumes (median reduction 0.5 and 1.5 Gy, p<0.001). Of the 46 patients, three patients' prostates and eight patients' SVs did not maintain dose coverage above 70 Gy. Rectal filling correlated with decreased percentage-volume of SV receiving 75.6, 70, and 60 Gy (p<0.02).
  
  
  CONCLUSIONS
  The 3-mm intrafractional margin was adequate for prostate dose coverage. However, a significant subset of patients lost SV dose coverage. The rectal volume change significantly affected SV dose coverage. For advanced-stage prostate cancers, we recommend to use larger margins or improve organ immobilization (such as with a rectal balloon) to ensure SV coverage.
authors: Department of Radiation Physics, The University of Texas M.D. Anderson Cancer Center, USA.
authors: Adam D
authors: AD
authors: Melancon
authors: Jennifer C
authors: JC
authors: O'Daniel
authors: Lifei
authors: L
authors: Zhang
authors: Rajat J
authors: RJ
authors: Kudchadker
authors: Deborah A
authors: DA
authors: Kuban
authors: Andrew K
authors: AK
authors: Lee
authors: Rex M
authors: RM
authors: Cheung
authors: Renaud
authors: R
authors: de Crevoisier
authors: Susan L
authors: SL
authors: Tucker
authors: Wayne D
authors: WD
authors: Newhauser
authors: Radhe
authors: R
authors: Mohan
authors: Lei
authors: L
authors: Dong
mesh_terms: D006801:Humans; D008297:Male; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D012669:Seminal Vesicles / Q000000981:diagnostic imaging; D014057:Tomography, X-Ray Computed