First Experience With Whole-Body Magnetic Resonance Imaging Using MET-RADS-P Criteria for Interim Efficacy Evaluation of 225Ac-PSMA Radioligand Therapy in Metastatic Castration-Resistant Prostate Cancer; 基于MET-RADS-P标准的全身磁共振成像在225Ac-PSMA放射性配体治疗转移性去势抵抗性前列腺癌中期疗效评估中的首次应用经验; Первый опыт применения магнитно-резонансной томографии всего тела с критериями MET-RADS-P в промежуточной оценке эффективности радиолигандной терапии препаратом 225Ac-ПСМА при метастатическом кастрационно-резистентном раке простаты

BACKGROUND: Radioligand therapy with actinium-225–prostate-specific membrane antigen (225Ac-PSMA) is a novel and promising treatment modality for metastatic castration-resistant prostate cancer. Whole-body magnetic resonance imaging (WB-MRI) is a noninvasive, non-ionizing imaging technique that provides comprehensive information on skeletal and extraskeletal metastatic lesions, structured using the MET-RADS-P (METastasis Reporting and Data System for Prostate Cancer) and enabling detailed assessment of treatment response. However, the use of this system has not been widely adopted, and its diagnostic accuracy requires clinical validation. AIM: This study aimed to evaluate the interim efficacy of 225Ac-PSMA radioligand therapy using WB-MRI based on MET-RADS-P criteria in patients with metastatic castration-resistant prostate cancer, assess method reproducibility (intra-observer agreement), and compare imaging findings with changes in prostate-specific antigen (PSA) levels. METHODS: WB-MRI was performed twice in patients with metastatic castration-resistant prostate cancer: before administration of 225Ac-PSMA-617 with activity 6–12 MBq and 1–2 months after a single cycle of radioligand therapy, with parallel measurement of PSA levels. Prospective response assessment was conducted using MET-RADS-P criteria for WB-MRI and PCWG criteria for PSA level trends. Reproducibility of MET-RADS-P criteria was evaluated through repeated reading of WB-MRI studies by the same radiologist with a 6-month interval. RESULTS: After one cycle of radioligand therapy, MET-RADS-P progression was identified in 4 of 20 patients with metastatic castration-resistant prostate cancer (20%) who completed the study. In three of these patients, progression was detected at an earlier time point than indicated by PSA level trends. More than half of the patients demonstrated discordant responses, including three with progression. Differences in PSA level trends were observed between concordant positive responses and various patterns of discordant response according to MET-RADS-P criteria. In cases of concordant response, the MET-RADS-P integrated assessment showed good correlation with biochemical response. MET-RADS-P criteria demonstrated excellent reproducibility for the primary response category pattern and for integrated response assessment. Reproducibility for the secondary response category pattern was substantial. CONCLUSION: The use of MET-RADS-P criteria to WB-MRI in patients with metastatic castration-resistant prostate cancer enabled earlier detection of progression in skeletal and extraskeletal lesions compared with PSA level trends and demonstrated good intra-observer agreement. Further investigation of the prognostic value of MET-RADS-P criteria in the context of 225Ac-PSMA radioligand therapy is warranted. © Eco-Vector, 2025.