title: Definition and visualisation of regions of interest in post-prostatectomy image-guided intensity modulated radiotherapy.
abstract: BACKGROUND
  Standard post-prostatectomy radiotherapy (PPRT) image verification uses bony anatomy alignment. However, the prostate bed (PB) moves independently of bony anatomy. Cone beam computed tomography (CBCT) can be used to soft tissue match, so radiation therapists (RTs) must understand pelvic anatomy and PPRT clinical target volumes (CTV). The aims of this study are to define regions of interest (ROI) to be used in soft tissue matching image guidance and determine their visibility on planning CT (PCT) and CBCT.
  
  
  METHODS
  Published CTV guidelines were used to select ROIs. The PCT scans (n = 23) and CBCT scans (n = 105) of 23 post-prostatectomy patients were reviewed. Details on ROI identification were recorded.
  
  
  RESULTS
  Eighteen patients had surgical clips. All ROIs were identified on PCTs at least 90% of the time apart from mesorectal fascia (MF) (87%) due to superior image quality. When surgical clips are present, the seminal vesicle bed (SVB) was only seen in 2.3% of CBCTs and MF was unidentifiable. Most other structures were well identified on CBCT. The anterior rectal wall (ARW) was identified in 81.4% of images and penile bulb (PB) in 68.6%. In the absence of surgical clips, the MF and SVB were always identified; the ARW was identified in 89.5% of CBCTs and PB in 73.7%.
  
  
  CONCLUSIONS
  Surgical clips should be used as ROIs when present to define SVB and MF. In the absence of clips, SVB, MF and ARW can be used. RTs must have a strong knowledge of soft tissue anatomy and PPRT CTV to ensure coverage and enable soft tissue matching.
authors.affiliation: Radiation Oncology Department, Northern Sydney Cancer Centre, Royal North Shore Hospital St Leonards, New South Wales, Australia ; Faculty of Health Sciences, University of Sydney Lidcombe, New South Wales, Australia.
authors.forename: Linda J
authors.initials: LJ
authors.lastname: Bell
authors.affiliation: Radiation Oncology Department, Northern Sydney Cancer Centre, Royal North Shore Hospital St Leonards, New South Wales, Australia ; Faculty of Health Sciences, University of Sydney Lidcombe, New South Wales, Australia.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Cox
authors.affiliation: Radiation Oncology Department, Northern Sydney Cancer Centre, Royal North Shore Hospital St Leonards, New South Wales, Australia.
authors.forename: Thomas
authors.initials: T
authors.lastname: Eade
authors.affiliation: Radiation Oncology Department, Northern Sydney Cancer Centre, Royal North Shore Hospital St Leonards, New South Wales, Australia.
authors.forename: Marianne
authors.initials: M
authors.lastname: Rinks
authors.affiliation: Radiation Oncology Department, Northern Sydney Cancer Centre, Royal North Shore Hospital St Leonards, New South Wales, Australia.
authors.forename: Andrew
authors.initials: A
authors.lastname: Kneebone
keywords: CBCT; IGRT; post prostatectomy; radiotherapy; regions of interest