RT Journal Article SR Electronic T1 Clinical relevance of post-therapy SPECT/CT in prostate cancer patients treated with Lutetium Lu 177 vipivotide tetraxetan JF Journal of Nuclear Medicine JO J Nucl Med FD Society of Nuclear Medicine SP 242599 OP 242599 VO 65 IS supplement 2 A1 Prasad, Vikas A1 Kim, Hyun A1 Michalski, Jeff A1 Laforest, Richard A1 Picus, Joel A1 Pachynski, Russell A1 Gay, Hiram A1 Reimers, Melissa A1 Wahl, Richard A1 Dehdashti, Farrokh YR 2024 UL http://jnm.snmjournals.org/content/65/supplement_2/242599.abstract AB 242599 Introduction: Lu-177 PSMA-617 (Lutetium Lu 177 vipivotide tetraxetan) is approved for the treatment of metastasized castrate-resistant prostate cancer patients progressing after at least one line of novel axis androgen deprivation therapy and one of the taxane-based therapies. PCWG3 criteria is currently used for the follow-up of these patients, which may be misleading in some patients. This retrospective study looked at the clinical relevance of SPECT/CT performed following Lutetium Lu 177 vipivotide tetraxetan which are performed as part of our standard of care.Methods: After IRB approval, charts of patients treated with Lutetium Lu 177 vipivotide tetraxetan and referred to our Theranostic Tumor Board (TTB) were retrospectively evaluated. SPECT/CT images (noncontrast-enhanced low dose CT) were acquired from vertex to mid-thigh at an early time point (same day) or delayed (next day or later) based on clinical logistical considerations. SPECT/CT results were categorized by a single experienced nuclear medicine physician without use of laboratory data in the following groups: group 1: favorable response - decrease in intensity of expression and/ or number of the lesions, group 2: progressive disease - patients with new and/or progressive lesions on SPECT and/ or CT component of the SPECT/CT, group 3: neither PD nor favorable response including mixed response, and group 4: other clinically relevant non tumor related findingsResults: Out of the 68 patients recommended for Lutetium Lu 177 vipivotide tetraxetan therapy, 22 patients did not get any SPECT/CT at the time of analyses of the data mainly due to insurance or logistical issues (5 were treated in a clinical trial). Forty-six patients underwent SPECT/CT either on the same day (n=8; 17.4%) or next day or later (n=38; 82.6%). The mean age of these patients was 69 ± 9 years. Patients received a median of 3 cycles (range 1-6). A total of 131 SPECT/CTs were performed. Results of the SPECT/CT showed favorable response in 14 (30%) of patients whereas 21 (45.6%) belonged to group 3. Progressive disease was observed in 8 (17.4%) of patients. We observed hydronephrosis, new fracture, lesion suitable for biopsy and pleural effusion in one patient each (group 4).Conclusions: Post-Lutetium Lu 177 vipivotide tetraxetan SPECT/CT scans appear to provide clinically meaningful information some of which cannot be determined by serum PSA alone and should strongly be considered for performance in all patients after every cycle.