title: Accumulation of rectum dose-volume metrics for prostate external beam radiotherapy combined with brachytherapy: Evaluating deformably registered dose distribution addition using parameter-based addition.
abstract: BACKGROUND
  To investigate the accuracy of deriving dose-volume histogram (DVH) parameters from deformably registered data by comparing values with the simple addition of DVHs from each phase of a combined external beam radiotherapy (EBRT)/high-dose-rate (HDR-BT) brachytherapy prostate treatment.
  
  
  METHODS
  Eighty-two patients received EBRT in 23 fractions of 2 Gy and HDR-BT TG43 in three fractions of 6.5 Gy. The HDR-BT CT was deformably registered to the EBRT CT. The rectum D0.1cc, D1cc, D2ccand D10ccwere calculated in two ways. (i) Parameter-adding: the EBRT DVH parameters (or the EBRT prescription dose) were added to the unregistered HDR-BT DVH parameters. (ii) Distribution-adding: the parameters were extracted after the EBRT doses were 3D-summed with the registered HDR-BT doses. Resulting differences between the parameters were investigated.
  
  
  RESULTS
  The D0.1cc, D1ccand D2ccfrom parameter-adding were 21.3% (P < 0.001), 6.3% (P < 0.001) and 3.5% (P < 0.001) smaller than those from distribution-adding. The D10ccwas 2.2% (P = 0.015) larger for distribution-adding.
  
  
  CONCLUSIONS
  Distribution-adding was confounded by unsystematic inter/intra-observer rectum-contouring errors and registration accuracy near the anterior rectal wall. Consequently, clinical use of distribution-adding to assess rectal doses requires careful contour and registration evaluation.
authors.affiliation: School of Physics, University of Western Australia, Crawley, Western Australia, Australia.
authors.forename: Calyn R
authors.identifier: http://orcid.org/0000-0001-9752-7308
authors.initials: CR
authors.lastname: Moulton
authors.affiliation: School of Physics, University of Western Australia, Crawley, Western Australia, Australia.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: House
authors.affiliation: Radiation Oncology, Sir Charles Gairdner Hospital, Nedlands, Western Australia, Australia.
authors.forename: Victoria
authors.initials: V
authors.lastname: Lye
authors.affiliation: Radiation Oncology, Sir Charles Gairdner Hospital, Nedlands, Western Australia, Australia.
authors.forename: Colin I
authors.initials: CI
authors.lastname: Tang
authors.affiliation: Radiation Oncology, Sir Charles Gairdner Hospital, Nedlands, Western Australia, Australia.
authors.forename: Michele
authors.initials: M
authors.lastname: Krawiec
authors.affiliation: Radiation Oncology, Sir Charles Gairdner Hospital, Nedlands, Western Australia, Australia.|School of Surgery, University of Western Australia, Crawley, Western Australia, Australia.
authors.forename: David J
authors.initials: DJ
authors.lastname: Joseph
authors.affiliation: School of Medicine and Population Health, University of Newcastle, Callaghan, New South Wales, Australia.
authors.forename: James W
authors.initials: JW
authors.lastname: Denham
authors.affiliation: School of Physics, University of Western Australia, Crawley, Western Australia, Australia.|Radiation Oncology, Sir Charles Gairdner Hospital, Nedlands, Western Australia, Australia.
authors.forename: Martin A
authors.initials: MA
authors.lastname: Ebert
mesh_terms: D001918:Brachytherapy; D019583:Dose Fractionation, Radiation; D006801:Humans; D008297:Male; D009367:Neoplasm Staging; D011471:Prostatic Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D011829:Radiation Dosage; D011874:Radiometry / Q000379:methods; D011879:Radiotherapy Dosage; D012007:Rectum / Q000528:radiation effects*
keywords: Brachytherapy; computer-assisted radiotherapy; computer-assisted radiotherapy planning; image-guided radiation therapy; prostate cancer