The diagnostic value of whole-body HYNIC-PSMA 11 -Tc [99 mTc] SPECT/CT scan in early staging of patients with moderate- and high-risk prostate cancer.

Objective: This prospective study aims to compare the diagnostic yield of conventional imaging modalities, including CT scan, bone scan, with ^{99 m}Tc-HYNIC-PSMA-11, in detecting local and distant metastases for initial staging in treatment-naïve, intermediate- to high-risk prostate cancer (PCa) patients. ⁶⁸ Ga-PSMA or 18F-PSMA PET/CT scans are known as the preferred modalities for staging this kind of patients, but there are limited PET/CT facilities in developing countries.

Materials and methods: A total of 63 treatment-naïve PCa patients were included in the study for the initial staging. Each patient underwent a chest and abdominopelvic CT scan, bone scan, and ^{99 m}Tc-HYNIC-PSMA-11 imaging. ^{99 m}Tc-HYNIC-PSMA-11 (20-25 mCi) and ^{99 m}TC-MDP (20-25 mCi) were administered intravenously, and imaging was performed 3-4 h post-injection. Nuclear scans included whole-body imaging with SPECT or SPECT/CT phases in two fields (thorax and abdominopelvic), along with imaging of suspicious areas. All images were independently interpreted and analyzed on a patient-based and region-based level.

Results: Region-based analysis revealed osseous metastatic regions in 78 (median 0 per patient, range 0-9), 25, and 87 (median 2 per patient, range 0-9) regions in the PSMA-11 scan, CT scan, and bone scan, respectively. CT scan was limited in assessing all nine osseous regions due to its restricted field of view. The positive detection rate for local lymph-node and distant metastases (distant lymphatic, osseous, and visceral) was 18/63 (28.6%) and 23/63 (41.3%) for the PSMA-11 scan, and 20/63 (31.8%) and 27/63 (42.9%) for the CT scan, with no significant difference between the two modalities. Overall, the combined findings of the PSMA-11 scan, CT scan, and bone scan were positive in 31/63 (49.2%), 34/63 (53.9%), and 32/63 (50.8%) patients, respectively. Equivocal findings were reported in 1 PSMA-11 scan, 13 CT scans, and 4 bone scans. When equivocal findings were considered as positive for metastasis, the accuracy, sensitivity, and specificity were 78.2%, 60%, and 96.4% for the PSMA-11 scan; 76.1%, 62.9%, and 89.3% for the CT scan; and 85%, 78.6%, and 91.4% for the bone scan. There was a strong agreement in disease staging and overall findings between the PSMA-11 scan and the combination of CT and bone scans (Ƙ = 0.949 and Ƙ = 0.905, respectively; p < 0.001).

Conclusion: The comparable accuracy and high concordance between ^{99 m}Tc-HYNIC-PSMA-11 and conventional CT and bone scans make ^{99 m}Tc-HYNIC-PSMA-11 an effective method for initial staging of intermediate- to high-risk prostate cancer patients.