title: An adaptive radiotherapy planning strategy for bladder cancer using deformation vector fields.
abstract: OBJECTIVE
  Adaptive radiotherapy (ART) has considerable potential in treatment of bladder cancer due to large inter-fractional changes in shape and size of the target. The aim of this study was to compare our clinically applied method for plan library creation that involves manual bladder delineations (Clin-ART) with a method using the deformation vector fields (DVFs) resulting from intensity-based deformable image registrations (DVF-based ART).
  
  
  METHODS
  The study included thirteen patients with urinary bladder cancer who had daily cone beam CTs (CBCTs) acquired for set-up. In both ART strategies investigated, three plan selection volumes were generated using the CBCTs from the first four fractions; in Clin-ART boolean combinations of delineated bladders were used, while the DVF-based strategy applied combinations of the mean and standard deviation of patient-specific DVFs. The volume ratios (VRs) of the course-averaged PTV for the two ART strategies relative the non-adaptive PTV were calculated.
  
  
  RESULTS
  Both Clin-ART and DVF-based ART considerably reduced the course-averaged PTV, compared to non-adaptive RT. The VR for DVF-based ART was lower than for Clin-ART (0.65 vs. 0.73; p<0.01).
  
  
  CONCLUSIONS
  DVF-based ART for bladder irradiation has a considerable normal tissue sparing potential surpassing our already highly conformal clinically applied ART strategy.
authors.affiliation: Department of Medical Physics, Aarhus University Hospital, Denmark. Electronic address: annveste@rm.dk.
authors.forename: Anne
authors.initials: A
authors.lastname: Vestergaard
authors.affiliation: Department of Clinical Experimental Oncology, Aarhus University Hospital, Denmark.
authors.forename: Jesper Folsted
authors.initials: JF
authors.lastname: Kallehauge
authors.affiliation: Department of Medical Physics, Aarhus University Hospital, Denmark.
authors.forename: Jørgen Breede Baltzer
authors.initials: JB
authors.lastname: Petersen
authors.affiliation: Department of Oncology, Aarhus University Hospital, Denmark.
authors.forename: Morten
authors.initials: M
authors.lastname: Høyer
authors.affiliation: Department of Oncology, Aarhus University Hospital, Denmark.
authors.forename: Jimmi
authors.initials: J
authors.lastname: Søndergaard
authors.affiliation: Department of Medical Physics, Aarhus University Hospital, Denmark.
authors.forename: Ludvig Paul
authors.initials: LP
authors.lastname: Muren
mesh_terms: D000368:Aged; D054893:Cone-Beam Computed Tomography / Q000379:methods*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D001743:Urinary Bladder / Q000000981:diagnostic imaging; D001749:Urinary Bladder Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*
keywords: ART; Adaptive; Bladder cancer; Deformation vector fields; Normal tissue sparing; Plan selection