High-Intensity Focused Ultrasound in Prostate Cancer: Can PSMA PET Improve Focal Therapy Outcomes?

Abstract

High-intensity focused ultrasound (HIFU) is an increasingly used, locally ablative therapy option in localized prostate cancer (PCa). Multiparametric MRI (mpMRI) is currently used for tumor delineation. However, up to 56% of patients will have recurrent disease, defined as International Society of Urological Pathology (ISUP) grade of 2 or greater on follow-up biopsies within 3 y. The objectives of this study were to evaluate recurrence and failure-free survival (FFS) rates in patients treated with HIFU after undergoing prostate-specific membrane antigen (PSMA) PET and to compare delineation and scoring for biopsy-proven lesions between imaging techniques (PSMA PET vs. mpMRI). <b>Methods:</b> This single-center retrospective cohort study included all patients who were scheduled for HIFU between June 2017 and May 2022 and underwent a PSMA PET scan within 6 mo before planned HIFU for initial therapy of low-risk or intermediate-risk PCa (primary HIFU) or local recurrence after radiotherapy (salvage HIFU). Outcomes assessed included FFS, defined as the absence of ISUP grade 2 or greater on follow-up biopsies, progression on imaging, or biochemical recurrence. Tumor detection on mpMRI and PSMA PET was compared using PRIMARY and Prostate Imaging Reporting and Data System (PI-RADS) 2.1 scores for patients with adequate mpMRI and PSMA PET within 6 mo of HIFU. <b>Results:</b> Of the 26 patients included in the cohort, 3 (12%) did not undergo HIFU after the PSMA PET scan because of PCa upstaging. Of the remaining 23 patients, 9 (39%) were treated for recurrent disease and 14 (61%) for primary disease. Over a mean follow-up time of 3.2 y, 15 patients (65%; 95% CI, 42.7%-83.6%) were free of disease at the last follow-up. Eight patients (35%) experienced recurrent or residual disease within 3 y. Image analysis was performed for 18 patients, for a total of 23 lesions, with mean PRIMARY and PI-RADS 2.1 scores of 4.1 (range, 2-5), and 3.3 (range, 2-5), respectively. Lesion detection was rated superior on PET over mpMRI for 12 lesions, whereas mpMRI was superior for 1 lesion. <b>Conclusion:</b> PSMA PET scans performed before HIFU identified 12% of patients who were unsuitable for treatment. The overall improved FFS rate and higher PRIMARY score, when compared with the existing literature, suggest a potential benefit of PSMA PET for tumor delineation.