Comparative assessment of 18F-PSMA-1007 biodistribution at 60 and 120 minutes after administration by PET/CT in prostate cancer patients

INTRODUCTION: Positron emission tomography combined with computed tomography (PET/CT) with prostate-specific membrane antigen-targeted (PSMA) radiopharmaceuticals is a valuable method for prostate cancer (PCa) imaging. Both 68Ga- and 18F-labelled PSMA ligands are used in clinical practice now, for example, 18F-PSMA-1007. Currently there is no consensus on time interval between 18F-PSMA-1007 administration and scanning start that served as the basis for this study. OBJECTIVE: The aim of this study was to determinate the optimal time interval between 18F-PSMA-1007 administration and scanning start at PET/CT in PCa patients.  

MATERIALS AND METHODS: This prospective analysis included the results of 18F-PSMA-1007 PET/CT of 26 patients with PCa (mean age — 69.1±7.1 years, mean PSA value — 3.9 (0.5; 10) ng/ml), 4 patients — at primary staging, 10 patients — with therapy assessment and 12 patients — with biochemical recurrence. The PET/CT scanning was performed at 60 and 120 minutes after 18F-PSMA-1007 administration with subsequent measurement and comparison of the pathological and physiological uptake. TBR value (Tumor-to-Background Ratio) was calculated for the pathological uptake in the prostate or prostate bed and lymph nodes lesions relative to the physiological uptake in urinary bladder and abdominal aortic blood pool respectively. Statistics: Statistical analysis was carried out using the software SPSS Statistics 28 to analyse the significance of the differences in median SUVmax (for pathological 18F-PSMA-1007 uptake), SUVmean (for physiological 18F-PSMA-1007 uptake) and TBR between two stages of scanning.  

RESULTS: There was a significant decrease of physiological 18F-PSMA-1007 uptake from median SUVmean 1.5 (1.0; 1.73) to 0.9 (0.5; 0.9), p<0.001 in the abdominal aortic blood pool, 2.6 (1.3; 3.6) to 1.7 (1.1; 2.8), p<0.05 in the urinary bladder, 0.4 (0.35; 0.44) to 0.33 (0.3; 0.37), p<0.05 in the right gluteus medius muscle in the second scan. Moreover, there was a significant increase of physiological 18F-PSMA-1007 uptake from median SUVmean 8.9±2.8 to 10.3±3.4, p<0.001 in the liver, 7.5±3.5 to 8.3±3.8, p<0,001 in the spleen, 9.8±3.7 to 11.6±4.3, p<0.001 in the right parotid salivary gland. Uptake in the bone marrow remained stable with median SUVmean 1 (0.8; 1.3), p=0.917. There was a significant increase of pathological uptake from median SUVmax 4.6 (2.7; 7.7) to 5.25 (3.2; 9.0), p<0.001 in 76 lesions without appearance of new lesions in the second scan at 120 minutes. Mean TBR value also significantly increased for the ratios «prostate or prostate bed/urinary bladder» from 1.7 (1.1; 4.7) to 3.6 (2.1; 9.5), p<0.05 and «lymph node/aortic blood pool»: per-lesion analysis from 2.8 (2.5; 5.2) to 6.2 (5; 10.1), p<0.001 and per-patient analysis from 4,6 (2.7; 5.5) to 9.8 (4.9; 12.1), p<0.05.  

DISCUSSION: It’s not justified to use time interval in 120 minutes routinely because of the lack of new lesions in the second scan, irrational spending of the department resources and time of medical staff. However, there was an increase in the TBR values indicating the higher quality of images in the second scan at 120 minutes.  

CONCLUSION: Due to the lack of clinical benefits of the 120 minutes interval and the associated time cost, a 60 minutes interval between 18F-PSMA-1007 administration and the start of a PET/CT scan in PCa patients is more optimal, however, delayed scan is justified in cases of obtaining unclear results. 

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