We evaluated quantitative changes in total metastatic tumor burden in patients with metastatic castration-resistant prostate cancer undergoing prostate-specific membrane antigen radioligand therapy (PSMA RLT) using single photon emission computed tomography/computed tomography (SPECT/CT). This retrospective two-center study included 331 patients treated with PSMA RLT. SUVmean, SUVmax, and total tumor volume (TTV) were measured using post-treatment SPECT/CT, and median percentage changes were calculated. Patients received a median of 3 RLT doses, and the prostate-specific antigen (PSA50) response rate was 58.4%. Early responders (≥30% TTV reduction between cycles 1 and 2; n = 187, 56.5%) demonstrated a 61.3% TTV reduction at cycle 2, with continued reductions in subsequent cycles. Minimal responders (<30% TTV reduction; n = 144, 43.5%) showed modest, gradual decreases across cycles (-1.4% at cycle 2, -26.5% at cycle 3, and -67.6% at cycle 6). A modest positive correlation was observed between PSA and TTV changes (r = 0.318, p < 0.001); however, 43.6% of patients exhibited PSA-TTV discordance. Early responders experienced smaller reductions in tumor burden in later cycles than minimal responders. These findings suggest that dynamic changes in TTV on SPECT/CT can be used to guide RLT strategy.
European urology oncology. 2026 Jun 30 [Epub ahead of print]
Moein Moradpour, Chae Moon Hong, Sobia Khan, Abuzar Moradi Tochayi, Surekha Yadav, Robert R Flavell, Louise Emmett, Thomas A Hope
Department of Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, CA, USA., Department of Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, CA, USA; Department of Nuclear Medicine, Kyungpook National University, Daegu, South Korea., Department of Theranostics and Nuclear Medicine, St. Vincent's Hospital, Sydney, New South Wales, Australia., Department of Theranostics and Nuclear Medicine, St. Vincent's Hospital, Sydney, New South Wales, Australia; Garvan Institute of Medical Research, Sydney, New South Wales, Australia; St. Vincent's Clinical School, University of New South Wales, Sydney, New South Wales, Australia., Department of Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, CA, USA; Helen Diller Family Comprehensive Cancer Center, University of California, San Francisco, CA, USA. Electronic address: .