title: Sensitivity of clinically relevant dosimetric parameters to contouring uncertainty in postimplant dosimetry of low-dose-rate prostate permanent seed brachytherapy.
abstract: There is strong evidence relating postimplant dosimetry for low-dose-rate prostate seed brachytherapy to local control rates. The delineation of the prostate on CT images, however, represents a challenge due to the lack of soft-tissue contrast to identify the prostate borders. This study aims at quantifying the sensitivity of prostate V100and D90to contouring uncertainty as clinically relevant parameters for evaluation of target coverage in postimplant dosimetry.
  
  
  
  CT images, postoperative plans, and contours of a cohort of patients (n = 43; low risk = 55.8%, intermediate risk = 39.5%, high risk = 4.7%), who had received prostate seed brachytherapy, were imported into MIM Symphony treatment planning system. The prostate contours in postimplant CT images were expanded or contracted uniformly in extents of ±1.00 mm, ±2.00 mm, ±3.00 mm, ±4.00 mm, and ±5.00 mm. The values for V100and D90were extracted from dose-volume histograms for each contour and compared.
  
  
  
  Significant changes were observed in the values of D90and V100as well as the number of inacceptable plans for expansion or contraction of only few millimeters. Evaluation of a plan coverage based on D90was found to be less sensitive to systematic contouring errors compared with V100. Number of plans incorrectly identified for lack or adequacy of coverage is lower using D90compared with V100for the same margin of error.
  
  
  
  Evaluation of a plan coverage based on V100is too sensitive to systematic contouring errors of prostate. D90increases the accuracy of CT-based postimplant quality assurance in identifying plans with insufficient coverage compared with V100.
authors.affiliation: Department of Medical Physics, Sunnybrook Odette Cancer Centre, Toronto, ON, Canada; Department of Radiation Oncology, University of Toronto, Toronto, ON, Canada. Electronic address: shahram.mashouf@sunnybrook.ca.
authors.forename: Shahram
authors.initials: S
authors.lastname: Mashouf
authors.affiliation: Sunnybrook Research Institute, Sunnybrook Health Sciences Centre, Toronto, ON, Canada.
authors.forename: Habib
authors.initials: H
authors.lastname: Safigholi
authors.affiliation: Department of Radiation Oncology, Sunnybrook Odette Cancer Centre, Toronto, ON, Canada; Department of Radiation Oncology, University of Toronto, Toronto, ON, Canada.
authors.forename: Tomas
authors.initials: T
authors.lastname: Merino
authors.affiliation: Sunnybrook Research Institute, Sunnybrook Health Sciences Centre, Toronto, ON, Canada.
authors.forename: Abraam
authors.initials: A
authors.lastname: Soliman
authors.affiliation: Department of Medical Physics, Sunnybrook Odette Cancer Centre, Toronto, ON, Canada; Department of Radiation Oncology, University of Toronto, Toronto, ON, Canada.
authors.forename: Ananth
authors.initials: A
authors.lastname: Ravi
authors.affiliation: Department of Radiation Oncology, Sunnybrook Odette Cancer Centre, Toronto, ON, Canada; Department of Radiation Oncology, University of Toronto, Toronto, ON, Canada.
authors.forename: Gerard
authors.initials: G
authors.lastname: Morton
authors.affiliation: Department of Medical Physics, Sunnybrook Odette Cancer Centre, Toronto, ON, Canada; Department of Radiation Oncology, University of Toronto, Toronto, ON, Canada; Sunnybrook Research Institute, Sunnybrook Health Sciences Centre, Toronto, ON, Canada.
authors.forename: William Y
authors.initials: WY
authors.lastname: Song
mesh_terms: D001918:Brachytherapy / Q000379:methods*; D006801:Humans; D007457:Iodine Radioisotopes / Q000627:therapeutic use; D008297:Male; D011182:Postoperative Care / Q000379:methods; D011184:Postoperative Period; D011467:Prostate / Q000000981:diagnostic imaging; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D019919:Prosthesis Implantation; D011874:Radiometry / Q000379:methods; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed / Q000379:methods; D035501:Uncertainty
chemical_list: D007457:Iodine Radioisotopes
keywords: D(90) and V(100); LDR prostate seed brachytherapy; Postimplant dosimetry; Prostate delineation