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

ÌÇÐÄ´«Ã½

Abstract

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.

View details for

View details for