By Francisco Osvaldo Garcia-Perez, MD, Department of Instituto Nacional de Cancerología, Tlalpan, Mexico City, Mexico and Lady Sawoszczyk, BS, CNMT, Siemens Healthineers Molecular Imaging, Hoffman Estates, Illinois, USA
Data and images courtesy of Instituto Nacional de Cancerología, Tlalpan, Mexico City, Mexico
Background
The overexpression of prostate-specific membrane antigen (PSMA) imaged through PET/CT and SPECT/CT agents is correlated with the malignancy of prostate cancer. Emerging data has shown the superiority of PSMA imaging with PET/CT over conventional imaging for primary prostate cancer diagnoses; however, access to PSMA imaging has been a challenge in low- and middle-income countries where high demand and expensive costs impede the growth of PSMA PET/CT imaging. In this case, a male in his 70s with PSMA-avid prostate cancer underwent 18F-PSMA-1007 PET/CT and 99mTc-iPSMA SPECT/CT imaging within a 24-hour interval to compare both agents in an effort to increase clinical utility.
History
A routine 18F-PSMA-1007 PET/CT was performed to stage a high-risk prostate cancer patient. PET/CT findings confirmed PSMA expression in the tumors. The patient was administered with 10.76 mCi (398.12 MBq) intravenous (IV) injection of 18F-PSMA-1007, and approximately 1 hour later, a whole-body acquisition was conducted on a Biograph™ PET/CT system.
Figure 1: Coronal CT, 18F-PSMA-1007 PET/CT, and coronal and sagittal PET MIP images confirm PSMA expression in metastatic disease.
Findings
As observed in Figure 1, 18F-PSMA-1007 PET/CT images demonstrate pelvic and retroperitoneal lymph node metastases.
The patient then underwent 99mTc-iPSMA SPECT/CT within a 24-hour interval to compare to the 18F-PSMA-1007 PET/CT PSMA expression. The patient was administered with 20 mCi (740 MBq) IV injection of 99mTc-iPSMA, and approximately 5 hours later, a multi-bed SPECT/CT was conducted on a Symbia™ SPECT/CT system. 99mTc-iPSMA SPECT/CT images in Figure 2 demonstrate similar PSMA-avid lesions in comparison to 18F-PSMA-1007 PET/CT.
The clinical value and accuracy of 99mTc-iPSMA SPECT/CT is demonstrated in Figures 3 and 4 when compared to 18F-PSMA-1007 PET/CT. In countries where PSMA imaging is not widely available, 99mTc-iPSMA SPECT/CT can play an integral role in expanding access to accurate prostate cancer diagnoses.
Figure 2: Coronal CT, 99mTc-iPSMA SPECT/CT, and coronal and sagittal SPECT MIP images confirm PSMA expression in lesions, which was previously confirmed in 18F-PSMA-1007 PET/CT.
Discussion
This case demonstrates the importance of imaging PSMA expression not only with PET/CT but also with SPECT/CT. According to the National Comprehensive Cancer Network (NCCN) Guidelines, it is recommended to perform PSMA imaging on patients with unfavorable intermediate-, high-, and very high-risk prostate cancer for primary staging. NCCN guidelines also indicate that PSMA PET/CT can be an alternative to conventional imaging. As 1 in 8 men are diagnosed with prostate cancer worldwide, access to PSMA imaging will increasingly become a challenge in underdeveloped countries as demand increases. Besides prostate cancer staging, PSMA PET/CT imaging is also utilized to qualify patients with castrate-resistant prostate cancer for 177Lu-PSMA-617 treatment. 99mTc-iPSMA SPECT/CT may become a useful agent in qualifying patients in countries where PSMA PET/CT imaging is limited.1,2
Conclusion
99mTc-iPSMA SPECT/CT is useful in the initial diagnosis of patients with high-risk prostate cancer. 99mTc-iPSMA is an available alternative for staging prostate cancer in countries with emerging economies that lack the sufficient infrastructure such as cyclotrons or PET imaging. Although 99mTc-iPSMA SPECT/CT demonstrated a slightly lower lesion detectability compared to 18F-PSMA PET/CT, there was no impact on the patient’s initial staging nor treatment planning.
Examination protocol
Scanners: Biograph mCT 20 Excel PET/CT and Symbia T6 SPECT/CT