A Prospective First-In-Human Pilot Study 18F-DCFPyL Prostate-Specific Membrane Antigen Imaging on the RefleXion X1 Positron Emission Tomography-Computed Tomograpghy Subsystem in Patients with Prostate Cancer.

Purpose: The RefleXion X1 Medical Radiotherapy System (RefleXion Medical) is a novel radiation therapy (RT) device capable of delivering real-time positron emission tomography (PET) scan-guided or biology-guided RT (BgRT). The purpose of this pilot study was to evaluate the performance of its PET imaging subsystem to detect 2-(3-{1-carboxy-5-[(6-[(18)F]fluoro-pyridine-3-carbonyl)-amino]-pentyl}-ureido)-pentanedioic acid (18F-DCFPyl) prostate-specific membrane antigen [PSMA] PET scan signal as the foundation for BgRT in patients with prostate cancer. Methods and Materials: Patients underwent a standard diagnostic 18F-DCFPyl PSMA PET scan. If at least 1 PET-scan-avid tumor was identified, the patient was then scanned on the RefleXion X1 unit. The target volume, activity concentration, and normalized target signal were determined, and BgRT planning was performed. Results: In 20 patients, at least 1 PSMA PET-scan-avid tumor was identified for BgRT planning (5 lymph node metastases, 7 bone metastases, 7 prostate glands, and 1 prostate bed). In 18 patients, the PET-scan-avid tumor was visualized on the RefleXion X1 PET scan, whereas in 2 patients, the tumor was too close to the PET scan activity in the bladder to be clearly visualized. BgRT planning was feasible and met stereotactic body RT organ dose constraints in 8 (40%) patients (3 prostate glands, 3 bones, and 2 lymph nodes). BgRT was not feasible in 12 (60%) patients because of low target activity concentration (<5 kBq/mL), low normalized target signal intensity (<2.7), or proximity of the PET-scan-avid tumor to the bladder. Conclusions: This is the first study to demonstrate the feasibility of using 18F-DCFPyl scan imaging for BgRT planning on the RefleXion X1 system in patients with prostate cancer. BgRT using targeted PET scan radiopharmaceuticals to guide RT represents a promising new dimension in radiation oncology and warrants further investigation.