Prostate-Specific Membrane Antigen
PET imaging with Cartesion Prime

Kevin L. Berger, MD
Director of PET-CT
Chesapeake Medical Imaging, MD

It is estimated that 288,300 new cases of prostate cancer will be diagnosed in the United States in 2023.¹ Prostate cancer significantly impacts quality of life and is a leading cause of cancer-related mortality and morbidity. Novel PET imaging tracers, designed to target the Prostate-Specific Membrane Antigen (PSMA) overexpressed in prostate cancer cells,² have shown very promising results in the management of prostate cancer patients. F-18 and Ga-68 based PSMA PET imaging agents have recently received FDA clearance for imaging of patients with suspected prostate cancer metastasis who are candidates for therapy or suspected recurrence based on elevated prostate-specific antigen (PSA) level.³ The National Comprehensive Cancer Network (NCCN) guidelines and Society of Nuclear Medicine and Molecular Imaging (SNMMI) Appropriate Use Criteria (AUC) were recently expanded to allow PSMA PET imaging for screening of patients to determine eligibility for PSMA-targeted radioligand therapy with lutetium Lu-177 vipivotide tetraxetan (PLUVICTO^®).
This case study presents images from a PET-CT scan with the recently FDA-approved Flotufolastat F-18 (POSLUMA^®) PSMA PET imaging tracer. The images were acquired by Cartesion Prime PET-CT, an air-cooled Premium Digital TOF PET scanner manufactured by Canon Medical Systems.

An 81-year-old male, previously diagnosed with prostate cancer that was initially managed with prostatectomy and with radiotherapy after a subsequent relapse, presented with rising PSA of 2.2. The patient underwent PSMA PET-CT imaging with ¹⁸F-Flotufolastat to assess recurrence and determine the extent of disease.

PET-CT images were acquired using Cartesion Prime PET-CT after a 71-minute post injection delay of 8.4 mCi ¹⁸F-Flotufolastat via the left antecubital fossa. The workflow was streamlined using the variable bedtime (vBT) feature on Cartesion Prime PET-CT. VBT enabled acquisitions of the pelvic and proximal regions at three minutes per bed and shorter acquisitions of the remaining anatomy at two minutes per bed (Table 1). The bed overlap was set at 40.6%. The PET scan comprised six bed positions and the total PET scan time was 15 minutes. Images were reconstructed using ordered subset expectation maximization (OSEM) with 3 iterations and 12 subsets, point-spread-function and Gaussian postfilter with 6 mm full width at half maximum (FWHM). Acquired non-contrast low-dose CT data (Table 2) were reconstructed with AiCE for CT for attenuation correction and anatomic localization of PET abnormalities.

Table 1: PET Parameters

Region Covered	BMI	Injected Dose	Acquisition Time	Number of Beds	Uptake Time	PSA level	Reconstruction
Skull-Base to Mid-Thigh	25.8 kg/m2	8.4 mCi 18F-Flotufolastat	3 min/bed x 3 + 2 min/bed x 3	6	71 min	2.2 ng/ml	TOF Listmode, OSEM

Table 2: CT Parameters

Scan Mode	Collimation	kVp	mAs	HP	Rotation Time	Scan Range	Reconstruction
Helical	0.5 mm x 80	120	196	65	0.5 s	1074 mm	AiCE for CT*

The acquired PET data underwent processing that extracted and reconstructed shorter segments of the data, simulating shorter acquisition times. We will refer to this protocol as “time-cut”. PET images shown in Figure 2 correspond to the default clinical protocol described above (Table 1) and a “time-cut” protocol of six beds acquired at ninety seconds per bed. All images were reconstructed using OSEM with 3 iterations and 12 subsets, point-spread-function and Gaussian postfilter with 6 mm FWHM. Lesions can be visualized very well in images corresponding to both acquisitions (Figure 2).

PSMA PET imaging plays a significant and growing role in cancer patient management with the continuous advances in novel tracers, theranostics, new treatments, and PET technology. In this case, PSMA PET imaging with ¹⁸F-Flotufolastat and acquired with Cartesion Prime PET-CT resulted in images of excellent quality that assisted in the visualization of focal uptake in the left inferior bladder wall and guided subsequent patient management. Furthermore, the image quality of “time-cut” reconstructions showcased the possibility of PET acquisition time reduction for further potential workflow improvements with Cartesion Prime PET-CT.