RATE AND OUTCOMES OF SNMMI "RARELY APPROPRIATE" PSMA PET/CT SCAN USE IN INITIAL STAGING AND BIOCHEMICALLY RECURRENT PROSTATE CANCER.

PSMA-based PET imaging was first approved by the FDA in December 2021 for the initial staging of newly diagnosed prostate cancer and the management of biochemically recurrent disease. As a clinical aid, the Society of Nuclear Medicine and Molecular Imaging (SNMMI) provides updated appropriate use criteria for PSMA PET/CT, and these recommendations are largely mirrored by the NCCN imaging. This study aims to examine the prevalence and outcomes of PET PSMA scans ordered in scenarios where they would be considered rarely appropriate or inappropriate by the SNMMI. A retrospective analysis of 897 men who were staged with a Gallium-68 or F-18 piflufolastat (DCFPyL) PSMA PET/CT scan between July 2021 and March 2023 identified 32 men who completed a PSMA scan despite not meeting appropriate use criteria by the SNMMI. Patient clinical, pathological, and imaging characteristics were collected, including ordering provider of PSMA scan. The reference standard for a positive scan included either histopathology demonstrating prostate adenocarcinoma or a change of a bone lesion to blastic on follow-up imaging. Cases were also considered positive if they met at least three soft criteria, including a corresponding positive lesion in a different imaging modality, decrease in size or lesions following treatment, increase in size or lesions over time, clinical symptoms of malignancy, localized treatment for imaging finding, PSA increase without treatment, PSA decrease after treatment, and typical appearance of multifocal disease. Equivocal findings were considered negative. 5% (17/340) of PSMA scans performed for initial staging did not meet appropriate use criteria as they were performed on NCCN very low, low, or favorable intermediate risk patients. No patient (0/17) showed PSMA positivity from this inappropriately scanned group. Furthermore, 3% (15/557) of patients who received a PSMA for work-up of biochemical recurrence failed to meet appropriate use criteria due to an undetectable PSA preceding the PSMA scan (PSA <0.01ng/ml). 20% (3/15) of these patients had false positive findings. PSMA identified true positivity in nodal and bone metastasis in 7% (1/15) and the remainder had negative scans. Urologists (53%, 17/32) comprised the largest ordering specialty in inappropriate use, followed by hematology oncology (19%, 6/32) and radiation oncology (19%, 6/32) with the remaining scans being ordered by other specialists or internists. Inappropriate or rarely appropriate use of PSMA PET/CT occurs in a significant minority of patients within our health care system. Inappropriate scans yielded no positivity in initial staging and had significant false positivity in biochemically recurrent patients. Physicians most likely to inappropriately order PSMA PET/CT scans are urologists. Further education of providers and EMR-based interventions (such as best practice alerts) may help limit inappropriate use in the future. [ABSTRACT FROM AUTHOR]