The Importance of Multi-parametric MRI, PET/CT, and Biopsy for Identifying and Delineating the Extent of Intraprostatic Radiorecurrent Prostate Cancer: A Secondary Analysis of the F-SHARP Clinical Trial.

Background: Up to 50% of clinical recurrences after curative-intent prostate cancer radiation are intraprostatic radiorecurrences (IPRR). Salvage local therapy (SLT) is increasingly offered, particularly as focal SLT, to reduce toxicity due to prior radiation. Limited data exist on the relative value of MRI, PET/CT, and biopsy on SLT target delineation.

Objective: Compare MRI, PET/CT, and biopsy in patients with IPRR and the impact each modality has on identifying IPRR and defining the extent of prostatic involvement.

Design, Setting, And Participants: Secondary analysis of 62 patients enrolled in phase I/II clinical trial of salvage high-dose-rate brachytherapy.

Outcome Measurements And Statistical Analysis: The IPRR was delineated using each imaging modality and by defining the involved regions of the prostate on biopsy. The exact binomial distribution was used to estimate the sensitivity of MRI and PET/CT to detect IPRR. Exact conditional logistic regression was used to compare the tumor identified by MRI and PET/CT with the areas of biopsy involvement (gold standard) and estimate the proportion of patients with prostatic involvement outside of the image-defined targets.

Results And Limitations: The sensitivity for detecting the IPRR was 91.8% for MRI and 85.5% for PET/CT. Most patients had biopsy-proven cancer outside of the MRI-defined (70.5%) and PET/CT-defined target (73.8%). Delineating the brachytherapy target using imaging only would have missed the full extent of recurrence in 63.9%.

Conclusion: Although MRI and PET/CT are valuable, a thorough biopsy is a mandatory tool to avoid missing areas of imaging-occult prostatic involvement when delivering focal SLT.