68Ga-PSMA-11 PET/MR detects local recurrence occult on mpMRI in prostate cancer patients after HIFU.

Abstract

High-intensity focused ultrasound (HIFU) is a promising new modality for the treatment of localized prostate cancer (PCa). Follow up of patients is recommended with biopsies and multiparametric MRI (mpMRI). However, mpMRI in the postinterventional setting is often false negative. It was our aim to investigate if the new tracer targeting the prostate specific membrane antigen (Ga-PSMA-11) could be used to localize recurrent disease with PET/MR in patients with discrepant findings between mpMRI and template biopsies. Interim analysis of the first ten patients scanned between 09/2016-05/2018 with positive template biopsy and negative mpMRI after HIFU from an ongoing clinical trial (NCT02265159). All patients underwent a Ga-PSMA-11 PET/MRI within 3 months. Four prostatic quadrants were defined and for every quadrant suspicion for recurrence was rated on a 5 point Likert scale from definitely no recurrence (1) to highly suspicious for recurrence (5), with (4) used as cut off for suspected disease based on PET/MRI by one blinded reader. Ga-PSMA-11 uptake of suspicious lesions and background areas was measured with the maximum standardized uptake value (SUV). The apparent diffusion coefficient (ADC) values of lesions and background was given for each segment. PET/MRI scans were compared with the template biopsy results including corresponding Gleason Scores (GS), number of positive cores and tumor length. The quadrant-based sensitivity, specificity, positive and negative predictive value for PET/MRI was 55%, 100%, 100% and 85%, respectively. Patient based, PET/MRI was negative in four cases with GS3+4 and a tumor length between 0.1-3mm. All tumor lesions with GS4+3 or higher were detected on PET/MRI. Our preliminary results indicate that Ga-PSMA-11-PET/MR has the potential to localize PCa recurrence after HIFU occult on mpMRI.