title: Utilization of cone-beam CT for offline evaluation of target volume coverage during prostate image-guided radiotherapy based on bony anatomy alignment.
abstract: OBJECTIVE
  To assess target volume coverage during prostate image-guided radiotherapy based on bony anatomy alignment and to assess possibility of safety margin reduction.
  
  
  BACKGROUND
  Implementation of IGRT should influence safety margins. Utilization of cone-beam CT provides current 3D anatomic information directly in irradiation position. Such information enables reconstruction of the actual dose distribution.
  
  
  METHODS
  Seventeen prostate patients were treated with daily bony anatomy image-guidance. Cone-beam CT (CBCT) scans were acquired once a week immediately after bony anatomy alignment. After the prostate, seminal vesicles, rectum and bladder were contoured, the delivered dose distribution was reconstructed. Target dose coverage was evaluated by the proportion of the CTV encompassed by the 95% isodose. Original plans employed a 1 cm safety margin. Alternative plans assuming a smaller 7 mm margin between CTV and PTV were evaluated in the same way. Rectal and bladder volumes were compared with the initial ones. Rectal and bladder volumes irradiated with doses higher than 75 Gy, 70 Gy, 60 Gy, 50 Gy and 40 Gy were analyzed.
  
  
  RESULTS
  In 12% of reconstructed plans the prostate coverage was not sufficient. The prostate underdosage was observed in 5 patients. Coverage of seminal vesicles was not satisfactory in 3% of plans. Most of the target underdosage corresponded to excessive rectal or bladder filling. Evaluation of alternative plans assuming a smaller 7 mm margin revealed 22% and 11% of plans where prostate and seminal vesicles coverage, respectively, was compromised. These were distributed over 8 and 7 patients, respectively.
  
  
  CONCLUSIONS
  Sufficient dose coverage of target volumes was not achieved for all patients. Reducing of safety margin is not acceptable. Initial rectal and bladder volumes cannot be considered representative for subsequent treatment.
authors.affiliation: Department of Medical Biophysics, Faculty of Medicine in Hradec Kralove, Charles University in Prague, Czech Republic ; Department of Oncology and Radiotherapy, University Hospital, Hradec Kralove, Czech Republic.
authors.forename: Petr
authors.initials: P
authors.lastname: Paluska
authors.affiliation: Department of Medical Biophysics, Faculty of Medicine in Hradec Kralove, Charles University in Prague, Czech Republic.
authors.forename: Josef
authors.initials: J
authors.lastname: Hanus
authors.affiliation: Department of Oncology and Radiotherapy, University Hospital, Hradec Kralove, Czech Republic.
authors.forename: Jana
authors.initials: J
authors.lastname: Sefrova
authors.affiliation: Department of Oncology and Radiotherapy, University Hospital, Hradec Kralove, Czech Republic.
authors.forename: Lucie
authors.initials: L
authors.lastname: Rouskova
authors.affiliation: Department of Radiology, University Hospital, Hradec Kralove, Czech Republic.
authors.forename: Jakub
authors.initials: J
authors.lastname: Grepl
authors.affiliation: Department of Oncology and Radiotherapy, University Hospital, Hradec Kralove, Czech Republic.
authors.forename: Jan
authors.initials: J
authors.lastname: Jansa
authors.affiliation: Department of Oncology and Radiotherapy, University Hospital, Hradec Kralove, Czech Republic.
authors.forename: Linda
authors.initials: L
authors.lastname: Kasaova
authors.affiliation: Department of Oncology and Radiotherapy, University Hospital, Hradec Kralove, Czech Republic.
authors.forename: Miroslav
authors.initials: M
authors.lastname: Hodek
authors.affiliation: Department of Oncology and Radiotherapy, University Hospital, Hradec Kralove, Czech Republic.
authors.forename: Milan
authors.initials: M
authors.lastname: Zouhar
authors.affiliation: Department of Oncology and Radiotherapy, University Hospital, Hradec Kralove, Czech Republic.
authors.forename: Milan
authors.initials: M
authors.lastname: Vosmik
authors.affiliation: Department of Oncology and Radiotherapy, University Hospital, Hradec Kralove, Czech Republic.
authors.forename: Jiri
authors.initials: J
authors.lastname: Petera
keywords: Cone-beam computed tomography; Dose reconstruction; Dose-volume histogram; Image-guided radiotherapy; Prostate