Comparison of ⁹⁹Tc^m-PSMA SPECT/CT and ⁹⁹Tc^m-MDP SPECT/CT in the diagnosis of Bone Metastasis of Prostate Cancer

Introduction: The most common metastasis of prostate cancer (PCa) is bone metastasis. Skeletal-related event (SREs) can increase the risk of death in patients with PCa by 28%. ⁹⁹Tc^m-HYNIC-Glu-Urea-A (hereinafter referred to as: ⁹⁹Tc^m-PSMA) is a radionuclide labeled prostate-specific membrane antigen (PSMA) small molecular probe that can efficiently and specifically detect PCa lesions. The aim of our study was to investigate the difference between ⁹⁹Tc^m-PSMA SPECT/CT and ⁹⁹Tc^m-MDP SPECT/CT for the detection of bone metastasis in PCa.

Methods: A total 29 man who were pathologically confirmed PCa from October 2019 to February 2020 were prospectively enrolled in this study and gave informed consent under the guidance of the Ethics Board of Fujian Provincial Hospital. The median age was 69 (range, 61-87) years. The median PSA level was 2.15 (range, 0.003-906.2) ng/ml. They all underwent both⁹⁹Tc^m-PSMA SPECT/CT and ⁹⁹Tc^m-MDP SPECT/CT (Discovery NM/CT 670, with low energy high resolution collimators) at an average interval of 12.1days (at least 1 day). They did not receive any antineoplastic therapy during the two intervals. According to the examination results, they were divided into bone metastasis group and non-bone metastasis group. For all 29 patients, the positive and negative cases of bone metastasis diagnosed by the two methods were counted, and the diagnostic efficacy of the two methods were compared. The detected bone lesions were divided and scored according to specific anatomical areas, and according to the concentration of imaging agents and anatomical manifestations, it can be divided into "typical metastasis" and "equivocal metastasis". To analyze the uptake degree and difference of ⁹⁹Tc^m-PSMA and ⁹⁹Tc^m -MDP in bone lesions. Based on per bone lesion, the differences of the number of bone lesions detected by the two methods under different Gleason scores and PSA levels were compared.

Results: Among the 29 patients, 11 cases were diagnosed as bone metastasis and 18 cases without bone metastasis. For all 29 patients, there was no significant difference in the detection rate of bone metastases between the two methods (Kappa=0.590, P=0.219). The sensitivity of ⁹⁹Tc^m-PSMA SPECT/CT and ⁹⁹Tc^m-MDP SPECT/CT for the detection of bone metastasis was 100% and 90.9%, respectively, and there was no significant difference between them (P=1.0), but the specificity of ⁹⁹Tc^m-PSMA SPECT/CT was significantly higher than that of ⁹⁹Tc^m-MDP SPECT/CT (100% vs 72.8%, P=0.045). Based on per bone lesion, there was no significant difference in the concentration of ⁹⁹Tc^m-PSMA and ⁹⁹Tc^m -MDP in bone lesions(P=0.266,Z=-1.192); The proportion of "typical metastasis" and "equivocal metastasis" detected by the two methods was 6.4 (PSMA) and 1.3 (MDP) ,respectively. Under different PSA levels and Gleason scores, there was no significant difference in the number of bone lesions (1, 2, 3, 4, 5, > 5) detected by the two methods. However, in the follow-up, the number of false positives of bone lesions detected by ⁹⁹Tc^m-MDP SPECT/CT was more than that of ⁹⁹Tc^m-PSMA SPECT/CT(MDP,15 vs PSMA,0), and the 20 true positive bone lesions detected in ⁹⁹Tc^m-PSMA SPECT/CT were not detected in ⁹⁹Tc^m-MDP SPECT/CT.

Conclusions: The sensitivity of ⁹⁹Tc^m-PSMA SPECT/CT in the diagnosis of PCa bone metastasis was slightly higher than that of ⁹⁹Tc^m-MDP SPECT/CT, but there was no statistical difference. The specificity of ⁹⁹Tc^m-PSMA SPECT/CT in the diagnosis of bone metastasis of PCa is significantly better than that of ⁹⁹Tc^m-MDP SPECT/CT, and it can clearly diagnose the nature of bone lesions, and the diagnostic efficiency is higher than that of ⁹⁹Tc^m-MDP SPECT/CT. Because ⁹⁹Tc^m-PSMA SPECT/CT also has the function of specific diagnosis of PCa related lesions, it will have a wide application prospect.