title: Dynamic contrast enhanced MRI as a predictor of vascular-targeted photodynamic focal ablation therapy outcome in prostate cancer post-failed external beam radiation therapy.
abstract: BACKGROUND
  Photodynamic therapy (PDT) can be employed as a focal therapy for prostate cancer. Dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) can potentially help identify tumour recurrence after failed external-beam radiotherapy (EBRT). The purpose of this study was to determine the ability of DCE-MRI to predict early response to PDT salvage treatment.
  
  
  METHODS
  Patients with post-EBRT prostate cancer recurrence were prospectively enrolled into a Phase I/II trial of PDT using WST09. A 15-patient subgroup of this cohort undergoing 1.5T DCE-MRI at baseline and 1-week post-PDT was retrospectively analyzed. The reference standard was prostate biopsy obtained 6 months post-PDT. Analysis was performed on a patient-by-patient basis, by prostate gland halves, and by prostate sextants.
  
  
  RESULTS
  Biopsy 6 months post-PDT identified cancer in 10/15 patients (66.7%), and in 24/90 sextants (26.7%). Residual cancer was identified in 22/37 sextants (59.5%) identified as being involved at baseline. DCE-MRI at 1 week correctly predicted recurrent disease with a sensitivity of 100% (10/10), specificity of 60% (3/5), positive predictive value of 83.3% (10/12), negative predictive value of 100% (3/3), and an overall accuracy of 86.7%, (13/15). When analysis was performed on prostate halves, the sensitivity and negative predictive value remained at 100%, with an improvement in specificity to 88.2% (15/17). The overall accuracy of DCE-MRI was similar regardless of analysis method: 86.7% on a patient-by-patient basis, 86.7% by prostate half and 83.3% by sextant. Changes in prostate-specific antigen (PSA) did not correlate to response.
  
  
  CONCLUSIONS
  DCE-MRI shows promise as a tool to predict successful outcome when performed 1 week post-PDT and could potentially be used to inform the need for re-treatment at an early time-point.
authors.affiliation: Department of Medical Imaging, University Health Network, Toronto, ON;
authors.forename: Tristan
authors.initials: T
authors.lastname: Barrett
authors.affiliation: Division of Biophysics and Bioimaging, Ontario Cancer Institute, University Health Network, Toronto, ON;
authors.forename: Sean R H
authors.initials: SR
authors.lastname: Davidson
authors.affiliation: Division of Biophysics and Bioimaging, Ontario Cancer Institute, University Health Network, Toronto, ON;
authors.forename: Brian C
authors.initials: BC
authors.lastname: Wilson
authors.affiliation: Laboratory for Applied Biophysics, Ontario Cancer Institute, University Health Network, Toronto, ON;
authors.forename: Robert A
authors.initials: RA
authors.lastname: Weersink
authors.affiliation: Division of Urology, Department of Surgical Oncology, University Health Network, Toronto, ON;
authors.forename: John
authors.initials: J
authors.lastname: Trachtenberg
authors.affiliation: Department of Medical Imaging, Sunnybrook Health Sciences Centre and University of Toronto, Toronto, ON.
authors.forename: Masoom A
authors.initials: MA
authors.lastname: Haider