title: Deformable registration-based segmentation of the bowel on Megavoltage CT during pelvic radiotherapy.
abstract: During pelvic radiotherapy bowel loops (BL) are subject to inter-fraction changes. MVCT images have the potential to provide daily bowel segmentation. We assess the feasibility of deformable registration and contour propagation in replacing manual BL segmentation on MVCT. Four observers delineated BL on the planning kVCT and on one therapy MVCT in eight patients. Inter-observer variations in BLs contouring were quantified using DICE index. BLs were then automatically propagated onto MVCT by a commercial software for image deformation and subsequently manually corrected. The agreement between propagated BL/propagated+manually corrected BL vs manual were quantified using the DICE. Contouring times were also compared. The impact on DVH of using the deformable-registration method was assessed. The same procedures were repeated on high-resolution planning-kVCT and therapy-kVCT. MVCTs are adequate to visualize BL (average DICE: 0.815), although worse than kVCT (average DICE:0.889). When comparing propagated vs manual BL, a poor agreement was found (average DICE: 0.564/0.646 for MVCT/KVCT). After manual correction, average DICE indexes increased to 0.810/0.897. The contouring time was reduced to 15min with the semi-automatic approach from 30min with manual contouring. DVH parameters of propagated BL were significantly different from manual BL (p<0.0001); after manual correction, no significant differences were seen. MVCT are suitable for BL visualization. The use of a software to segment BL on MVCT starting from BL-kVCT contours was feasible if followed by manual correction. The method resulted in a substantial reduction of contouring time without detrimental effect on the quality of bowel segmentation and DVH estimates.
authors.affiliation: Medical Physics Department, IRCCS San Raffaele Scientific Institute, Milan, Italy. Electronic address: perna.lucia@hsr.it.
authors.forename: L
authors.initials: L
authors.lastname: Perna
authors.affiliation: Medical Physics Department, IRCCS San Raffaele Scientific Institute, Milan, Italy.
authors.forename: C
authors.initials: C
authors.lastname: Sini
authors.affiliation: Radiotherapy Department, IRCCS San Raffaele Scientific Institute, Milan, Italy.
authors.forename: C
authors.initials: C
authors.lastname: Cozzarini
authors.affiliation: Medical Physics Department, IRCCS San Raffaele Scientific Institute, Milan, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Agnello
authors.affiliation: Medical Physics Department, IRCCS San Raffaele Scientific Institute, Milan, Italy.
authors.forename: G M
authors.initials: GM
authors.lastname: Cattaneo
authors.affiliation: Department of Oncology and Medical Physics, Haukeland University Hospital, Bergen, Norway.
authors.forename: L B
authors.initials: LB
authors.lastname: Hysing
authors.affiliation: Department of Medical Physics, Aarhus University/Aarhus University Hospital, Aarhus, Denmark.
authors.forename: L P
authors.initials: LP
authors.lastname: Muren
authors.affiliation: Medical Physics Department, IRCCS San Raffaele Scientific Institute, Milan, Italy.
authors.forename: C
authors.initials: C
authors.lastname: Fiorino
authors.affiliation: Medical Physics Department, IRCCS San Raffaele Scientific Institute, Milan, Italy.
authors.forename: R
authors.initials: R
authors.lastname: Calandrino
mesh_terms: D005240:Feasibility Studies; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D007422:Intestines / Q000000981:diagnostic imaging*; D008297:Male; D015588:Observer Variation; D010388:Pelvis / Q000528:radiation effects*; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy; D011880:Radiotherapy Planning, Computer-Assisted; D013997:Time Factors; D014057:Tomography, X-Ray Computed
keywords: Bowel motion; Bowel segmentation; Deformable registration