Comparing the diagnostic efficacy of [99mTc]Tc-HYNIC-PSMA-11 SPECT/CT scanning after 75 minutes and 4 hours of radiotracer injection in men with prostate cancer

Introduction: Prostate-Specific Membrane Antigen (PSMA) is overexpressed in primary and metastatic prostate carcinoma (PCa) and could be targeted by a [99mTc]Tc-HYNIC-PSMA-11 scan for detection of metastases. Despite extensive studies, data on the most appropriate interval between radiopharmaceutical injection and image acquisition is scarce. We compared the metastasis detection rates of the [99mTc]Tc-HYNIC-PSMA-11 scan between 75-minute and 4-hour intervals of radiopharmaceutical injection. Methods: From May 2021 to May 2022, we studied 30 consenting men with pathologically confirmed PCa who were referred to our department requesting a PSMA scan for primary staging, biochemical recurrence, pre-177Lu-PSMA therapy, or surveillance. 75-minute and 4-hour [99mTc]Tc-HYNIC-PSMA-11 SPECT/CT scan performed following injection of the radiopharmaceutical. The corresponding metastasis detection rates were evaluated in 75-minute and 4-hour intervals. Results: The mean age of patients was 68.43 +/- 9.61 years, with a median PSA of 4.19 ng/ml and a median Gleason Score of 8. Nine cases had negative [99mTc]Tc-HYNIC-PSMA-11 scans, while 21 had positive scans (8 cases with bone, 2 with lung, 4 with lymph node, and 7 with multiple organ metastases). All metastases were detected in both checkpoints, except for one patient, where 75-minute images detected three pelvic metastatic lymph nodes, while four were seen in the 4-hour scan. This small missed right external iliac lymph node did not change the patient's management. Conclusion: We found no significant difference in the detection rate of metastatic lesions in 75-minute and 4-hour time intervals. These findings could help to decrease waiting time and by more efficient scheduling improves patient's satisfaction at nuclear medicine departments.