A male in his 70s with high-risk PSMA-avid prostate cancer underwent 18F-PSMA-1007 PET/CT and 99mTc-iPSMA SPECT/CT imaging for initial staging.

A comparative analysis of 99mTc-iPSMA SPECT/CT and 18F-PSMA-1007 PET/CT in the initial staging of a patient with high-risk prostate cancer

31/7/24


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

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.

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.

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.

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

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.

Scanners: Biograph mCT 20 Excel PET/CT and Symbia T6 SPECT/CT

18F-PSMA-1007 PET

 

Injected dose

10.76 mCi (398.12 MBq)

Post-injection delay

1 hour

Acquisition

Step-and-shoot method

 

CT

Tube voltage

140 kV

Tube current

41 mAs

Slice collimation

1.2 mm

Slice thickness

2.0 mm

 

 

99mTc-iPSMA SPECT

Injected dose

20 mCi (740 MBq)

Post-injection delay

5 hours

Acquisition

15 seconds per view, 60 views per detector

 

CT

Tube voltage

130 kV

Tube current

18 mAs

Slice collimation

0.6 mm

Slice thickness

5.0 mm

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