A comparative assessment of [99mTc] HYNIC-PSMA-11 scintigraphy in prostate cancer as a potential substitute for disease evaluation with [68Ga] PSMA-11 PET/CT imaging

OBJECTIVES: This study evaluated if [ 99m Tc]HYNIC-prostate-specific membrane antigen (PSMA)-11 scintigraphy presents a clinically viable imaging alternative to [ 68 Ga]PSMA-11 PET/computed tomography (CT) for disease evaluation in prostate cancer (PC). METHODS: In this prospective study, 106 patients diagnosed with prostate cancer were recruited. A total of 51 patients were assigned in the initial staging cohort and the remaining 55 patients in the re-staging cohort (comprising biochemical recurrence, metastatic castration-resistant prostate cancer, and metastatic hormone-sensitive prostate cancer). Imaging with [ 99m Tc] HYNIC-PSMA-11 was conducted within one week following [ 68 Ga]PSMA-11 PET/CT. Whole-body planar [ 99m Tc]HYNIC-PSMA-11 images were obtained at 2-, 4-h, and regional SPECT/CT at 3-h. A comparative detection efficiency of [ 99m Tc]HYNIC-PSMA-11 versus [ 68 Ga]PSMA-11 PET/CT was evaluated by consensus for the involved lesions/sites. A correlation analysis was carried out between maximum standardized uptake values of PSMA PET and percent quantitative lesion uptake values of PSMA SPECT. RESULTS: [ 68 Ga]PSMA-11 PET/CT detected 896 metastatic lesions, where HYNIC-PSMA-11 detected 761 lesions, offering an overall sensitivity of 85%. The sensitivity of [ 99m Tc] HYNIC-PSMA-11 SPECT/CT was 100% for primary/visceral lesions, 92% for skeletal lesions, 75.3% for distant lymph nodes and 67.4% for locoregional lymph nodes. A substantial agreement ( κ = 0.78, P < 0.0001) was seen between two imaging modalities. UCSF Cancer of the Prostate Risk Assessment score based disease staging matched with the disease staging demonstrated by both the imaging techniques. A significant ( P < 0.01) correlation was seen between the quantitative parameters of the two techniques both for primary ( r = 0.96) and metastatic ( r = 0.79 for skeletal and r = 0.65 for lymph nodes) lesions. CONCLUSION: [ 99m Tc]HYNIC-PSMA-11 SPECT/CT offers a potentially viable and cost-effective substitute for PSMA-PET for disease staging, quantification and response assessment to PSMA-targeted radiotherapies.