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CUAJ %u2022 FEBRUARY 2025 %u2022 VOLUME 19, ISSUE 2 %u00a9 2025 CANADIAN UROLOGICAL ASSOCIATION 17ORIGINAL RESEARCHINTRODUCTIONAccurate localization of biochemical recurrence (BCR) post-radical prostatectomy (RP) is necessary to inform salvage therapies. Conventional imaging, consisting of computed tomography (CT) and bone scintigraphy, can be expected to help detect recurrent disease in under 10% of men at the time of BCR.1 Positron emission tomography/computed tomography using a radiopharmaceutical that targets the prostate-specific member antigen (PSMA-PET/CT) is highly accurate in this setting, with a positive predictive value of 0.84 by histopathologic validation, with substantial interreader reproducibility, as PSMA-PET localizes recurrent prostate cancer in about 75% of patients in this setting.2 The detection rate increases as serum prostate-specific antigen (PSA) increases.2Up to 30% of patients were found to have at least one PSMAPET-positive lesion not covered by the Radiation Therapy Oncology Group (RTOG) consensus salvage radiotherapy (RT) fields.3 Prospective studies have suggested clinicians change their intended management after PSMA-PET in two-thirds of patients, a significantly increased rate compared to conventional CT restaging.4,5 The LOCATE trial, which enrolled men with a median PSA of 0.42 after RP, found 48% of patients had a management change, 16% of which was RT target modification.6The participants in this study were enrolled in the prospective, INTRODUCTION: This study aimed to assess the detection rate of prostate cancer recurrence by prostate-specific member antigen-positron emission tomography/computed tomography (PSMA-PET/CT) with 18F-DCFPyL in patients with residual disease or biochemical recurrence (BCR), and its association with surgical pathology and prostate-specific antigen (PSA) kinetics.METHODS: Men from South Central Ontario enrolled in the PSMA Registry for Recurrent Prostate cancer (PREP) between April 2019 and December 2021 after radical prostatectomy (RP) and who had 1) pathologic stage N1 or persistent elevated PSA; or 2) BCR (PSA >0.10 ng/mL) where initial postoperative PSA was undetectable were included.RESULTS: A total of 169 men (median age 68 years; interquartile range [IQR] 62%u201371) with complete data met the above criteria. The median PSA was 0.27 ng/mL (IQR 0.16%u20130.85) prior to PSMA-PET. Overall positivity rate 59%; when PSA was <0.40 ng/mL, overall positivity rate 42% vs. 85% with PSA %u22650.40 ng/mL (p<0.001). Higher pathologic tumor stage increased detection of regional lymph nodes (LNs) (pT2-3a: 32% vs. pT3b: 69%, p<0.001) but not distant metastases (pT2-3a: 12% vs. pT3b: 24%, p=0.15). PSMA-PET detected 18% with prostate bed, 42% with regional LN disease, and 44% with pelvic-only disease. The three most involved LN chains were the internal (21%) and external (20%) iliac, and obturator chains (16%).CONCLUSIONS: This prospective study of patients with residual disease or BCR after RP illustrates patterns of failure that could impact diagnosis and postoperative management. Such patients have significant risk of regional LN positivity on PSMA-PET, highlighting a need to include pelvic LNs within salvage radiotherapy volumes.ABSTRACT Samantha Sigurdson1, Khalid al Salman1, Aruz Mesci2, Ian Dayes1, Kimmen Quan1, Mira Goldberg1, Kara Schnarr1, Bobby Shayegan3, Glenn Bauman4, Katherine Zukotynski5, Theodoros Tsakiridis1, Himu Lukka11McMaster University and Juravinski Cancer Centre, Hamilton, ON, Canada; 2University of Toronto and Princess Margaret Cancer Centre, Toronto, ON, Canada; 3Division of Urology, Department of Surgery, McMaster University, Hamilton, ON, Canada; 4London Health Sciences Centre, London, ON, Canada; 5Departments of Medicine and Radiology, McMaster University, Hamilton, ON, CanadaCite as: Sigurdson S, al Salman K, Mesci A, et al. Patterns of failure with 18F-DCFPyL PSMA-PET/CT in the postprostatectomy setting: A regional cohort analysis. Can Urol Assoc J 2025;19(2):17-24. http://dx.doi.org/10.5489/cuaj.8859Published online October 7, 2024Appendix available at cuaj.caPatterns of failure with 18F-DCFPyL PSMA-PET/CT in the postprostatectomy settingA regional cohort analysis