The effectiveness of addition of early pelvik imaging to the routine Ga-68 PSMA PET/CT scaning in prostate cancer

Objective: This study aimed to retrospectively evaluate the efficacy of performing early pelvic imaging combined with routine whole-body Gallium-68 Prostate Specific Membrane Antigen Positron Emission Tomography/Computed Tomography (Ga-68 PSMA PET/CT) in patients diagnosed with prostate cancer who presented to our clinic for primary staging and restaging purposes. Materials and Methods: The images of 258 patients who underwent early pelvic and routine whole-body Ga-68 PSMA PET/CT for staging and restaging at the Department of Nuclear Medicine, Dicle University Medical Faculty, between January 2019 and March 2024, were retrospectively analyzed. Data on patients' age, prostate-specific antigen (PSA) levels, histopathological findings (Gleason score (GS) and International Society of Urological Pathology (ISUP) grade groups), Maximum Standardized Uptake Value (SUVmax), and Mean Standardized Uptake Value (SUVmean) were recorded. In this study, early pelvic images combined with standard imaging were compared to standard imaging alone, focusing on a detailed evaluation of the prostate gland, seminal vesicles, bladder, and pelvic lymph nodes. Measurements of tumor involvement in the prostate gland were obtained manually using a 40% threshold value. Results: A total of 258 male patients (178 for primary staging, 80 for restaging) were included in the study, with a median age of 67 years. Among all prostate cancer patients, there was a statistically significant difference in PSA levels between Ga-68 PSMA PET/CT-positive (229/258) and negative (29/258) patients (p<0.001). PSA levels, GS, and ISUP grade groups showed a moderate correlation with SUVmax and SUVmean values (Spearman correlation coefficients: for SUVmax, r = 0.406, 0.444, 0.431 (p<0.001); for SUVmean, r = 0.400, 0.426, 0.429 (p<0.001)). Adding early imaging to routine whole-body imaging provided a significantly higher detection rate, confirmed by Fisher's Exact test (p<0.001). Lesions not detected on standard imaging alone were identified exclusively with early pelvic imaging in 14 patients (5.4%), of whom 8 were in the primary staging group and 6 in the restaging group. Nonetheless, neither early pelvic nor standard images detected any lesions in 29 patients (11.3%). Conclusion: Early pelvic imaging combined with standard imaging provided better detection of prostate gland lesions and metastatic involvement of the bladder compared to standard imaging alone, and this difference was found to be statistically significant. This study recommends incorporating early pelvic imaging into routine whole-body Ga-68 PSMA PET/CT protocols. However, further prospective studies with larger patient cohorts and histopathological validation are necessary to assess the routine use of early imaging. Keywords: Prostate cancer, Ga-68 PSMA, Early Pelvic Imaging, Primary Staging, Restaging.