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

Introduction: 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. Conclusion: 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.

Final Results of a Phase I/II Multicenter Trial of WST11 Vascular Targeted Photodynamic Therapy for Hemi-Ablation of the Prostate in Men with Unilateral Low Risk Prostate Cancer Performed in the United States

“…26,27 mpMRI in treatment planning has been shown to be highly sensitive in the detection of residual tumor following VTP. 28 …”

DCE MRI of prostate cancer

“…Barrett and colleagues investigated the accuracy of DCE MRI for predicting patient response to photo-dynamic therapy (PDT) applied as salvage treatment for prostate cancer patients who previously underwent definitive external beam radiation therapy (EBRT). They found that DCE MRI performed one week into PDT accurately predicted disease recurrence with 100% sensitivity, 60% specificity, 83% positive predictive value, and 100% negative predictive value, and thus showed promise for assessing patient outcome [49]. Though the population size was small ( n = 15), the findings were encouraging and DCE MRI correlated better with patient outcome than prostate-specific antigen (PSA) levels, which decreased for 13/15 patients in the study.…”

Detection of Treatment Success after Photodynamic Therapy Using Dynamic Contrast-Enhanced Magnetic Resonance Imaging

“…These findings give rise to the hypothesis that DCE-MRI data correlates and matches spatially with tissue viability after PDT. Several reports of the use of contrast-enhanced MRI for PDT evaluation exist 18 , 19 , but to our knowledge, the spatial correspondence between (D)CE-MRI data and tumor treatment response has not been rigorously assessed.…”