A Pilot Study of 68Ga-PSMA11 and 68Ga-RM2 PET/MRI for Evaluation of Prostate Cancer Response to High Intensity Focused Ultrasound (HIFU) Therapy.

Rationale: Focal therapy for localized prostate cancer (PC) using high intensity focused ultrasound (HIFU) is gaining in popularity as it is non-invasive and associated with fewer side effects than standard whole-gland treatments. However, better methods to evaluate response to HIFU ablation are an unmet need. Prostate specific membrane antigen (PSMA) and gastrin-releasing peptide receptors (GRPR) are both overexpressed in PC. In this study, we evaluated a novel approach of using both 68Ga-RM2 and 68Ga-PSMA11 PET/MRI in each patient before and after HIFU to assess accuracy of target tumor localization and response to treatment. Methods: Fourteen men, 64.5 ± 8.0 (range 48-78) years-old, with newly diagnosed PC were prospectively enrolled. Pre-HIFU, patients underwent prostate biopsy, multiparametric MRI (mpMRI), 68Ga-PSMA11, and 68Ga-RM2 PET/MRI. Response to treatment was assessed at a minimum of 6 months after HIFU with prostate biopsy (n = 13), as well as 68Ga-PSMA11 and 68Ga-RM2 PET/MRI (n = 14). Maximum and peak standardized uptake values (SUVmax and SUVpeak) of known or suspected PC lesions were collected. Results: Pre-HIFU biopsy revealed 18 cancers of which 14 were clinically significant (Gleason score ≥3+4). mpMRI identified 18 lesions; 14 of them were ≥PI-RADS 4. 68Ga-PSMA11 and 68Ga-RM2 PET/MRI each showed 23 positive intraprostatic lesions; 21 were congruent in 13 patients and five were incongruent in 5 patients. Pre-HIFU, 68Ga-PSMA11 identified all target tumors while 68Ga-RM2 PET/MRI missed two tumors. Post-HIFU, 68Ga-RM2 and 68Ga-PSMA11 PET/MRI both identified clinically significant residual disease in one patient. Three significant ipsilateral recurrent lesions were identified, whereas one was missed by 68Ga-PSMA11. Pre-treatment prostate specific antigen (PSA) decreased significantly after HIFU by 66%. Concordantly, pre-treatment SUVmax decreased significantly after HIFU for 68Ga-PSMA11 (P = 0.001) and 68Ga-RM2 (P = 0.005). Conclusion: The results of this pilot study show that 68Ga-PSMA11 and 68Ga-RM2 PET/MRI identified the target tumor for HIFU in 100% and 86%, respectively, and accurately verified response to treatment. PET might be a useful tool in the guidance and monitoring of treatment success in patients receiving focal therapy for PC. These preliminary findings warrant larger studies for validation.

Journal of nuclear medicine : official publication, Society of Nuclear Medicine. 2022 Nov 03 [Epub ahead of print]

Heying Duan, Pejman Ghanouni, Bruce Daniel, Jarrett Rosenberg, Guido A Davidzon, Carina Mari Aparici, Christian Kunder, Geoffrey Sonn, Andrei Iagaru

Stanford University, United States.

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