RT Journal Article SR Electronic T1 Comparison of Posttherapy 4- and 24-Hour [177Lu]Lu-PSMA SPECT/CT and Pretherapy PSMA PET/CT in Assessment of Disease in Men with Metastatic Castration-Resistant Prostate Cancer JF Journal of Nuclear Medicine JO J Nucl Med FD Society of Nuclear Medicine SP 1939 OP 1944 DO 10.2967/jnumed.124.267606 VO 65 IS 12 A1 Swiha, Mina A1 Pathmanandavel, Sarennya A1 Papa, Nathan A1 Sabahi, Zahra A1 Li, Sherrington A1 Zheng, Alex A1 Khan, Sobia A1 Ayers, Maria A1 Sharma, Shikha A1 Crumbaker, Megan A1 Nguyen, Andrew A1 Chan, Lyn A1 Ayati, Narjess A1 Emmett, Louise YR 2024 UL http://jnm.snmjournals.org/content/65/12/1939.abstract AB [177Lu]Lu-prostate-specific membrane antigen (PSMA) is an effective treatment for metastatic castration-resistant prostate cancer (mCRPC). [177Lu]Lu-PSMA SPECT/CT 24 h after injection has shown potential as a response biomarker for [177Lu]Lu-PSMA therapy but is not convenient for patients. This study investigated 4-h [177Lu]Lu-PSMA SPECT/CT as an alternative to 24-h [177Lu]Lu-PSMA SPECT/CT for evaluation of treatment response. Methods: This prospective analysis enrolled 23 patients diagnosed with mCRPC commencing [177Lu]Lu-PSMA-I&T therapy. Two patients were excluded because of incomplete imaging data. Posttherapy SPECT/CT was performed at 4 and 24 h after the first dose and 4 h after the second dose. Baseline [68Ga]Ga-PSMA-11 PET/CT and 4- and 24-h [177Lu]Lu-PSMA SPECT/CT were analyzed both visually and semiquantitatively. Bland–Altman plots assessed agreement of semiquantitative parameters from the 4- and 24-h scans. Quantitative assessment of the change in the total tumor volume (TTV) on the 4-h [177Lu]Lu-PSMA SPECT/CT after the first and second doses was correlated to patient outcomes. Results: All patients had mCRPC previously treated with an androgen receptor pathway inhibitor, and 11 (52%) received prior taxane chemotherapy. Median age was 78 y, and median prostate-specific antigen level was 54 ng/mL. On visual analysis, disease distribution was unchanged among the 3 imaging methods. Eleven patients (52%) had a median of 1 lesion not identified on 4-h [177Lu]Lu-PSMA SPECT/CT compared with 24-h [177Lu]Lu-PSMA SPECT/CT. All missed lesions on the 4-h [177Lu]Lu SPECT/CT were smaller than 2 cm. Mean differences and agreement between 4- and 24-h SPECT/CT quantitative parameters were within acceptable bounds for lesion number, SUVmax, and SUVmean, with higher variation observed for TTV. The change in TTV between dose 1 and 2 [177Lu]Lu-PSMA SPECT/CT predicted prostate-specific antigen progression-free survival. Conclusion: [177Lu]Lu-PSMA SPECT/CT at 4 h after injection appears a promising alternative to 24-h [177Lu]Lu-PSMA SPECT/CT for treatment response assessment, with improved patient convenience.