1159 - A Prospective Pilot Study of [18F]-FDG Imaging with the PET-CT Subsystem on a Biology-Guided Radiotherapy Machine
Presenter(s)
C. Han1, S. Sampath1, S. Maroongroge1, S. V. Dandapani1, J. G. Bazan Jr1, A. Amini1, S. Szeja2, and J. Y. C. Wong1; 1Department of Radiation Oncology, City of Hope National Medical Center, Duarte, CA, 2Department of Radiation Oncology, City of Hope National Medical Center, Upland, CA
Purpose/Objective(s): The medical technology company’s X1 is a biology-guided radiotherapy system which is currently cleared by the Food and Drug Administration to deliver radiation to lung and bone lesions with real-time FDG positron-emission tomography (PET) guidance. The purpose of this single-institution study is to evaluate the performance of its PET imaging subsystem for patients with various 18F-FDG avid non-lung and non-bone malignancies.
Materials/Methods: Patients scheduled for a standard-of-care (SOC) 18F-FDG PET/CT scan were enrolled. Upon completion of the SOC PET/CT scan on a diagnostic (non-X1) PET/CT system, images were transferred to a radiotherapy planning system for PET-avid tumor target contouring. If at least one non-bone or non-lung PET-avid lesion was identified, the patient was then scanned on the X1 unit. The target volume, activity concentration (AC) and normalized target signal (NTS) were determined and BgRT planning was performed. A gross target volume (GTV) was drawn on the SOC PET/CT images for the PET-avid lesion, a planning target volume (PTV) was defined as a 5-mm isotropic expansion of the GTV, and a biology tracking zone (BTZ) was defined as a 5-mm isotropic expansion of the PTV. PET guidance is achieved by monitoring PET signals within the BTZ. To ensure sufficient PET signal strength from the tumor to guide BgRT delivery, AC must be at least 5 kBq/ml and NTS must be at least 2.7.
Results: Thirteen patients completed both SOC PET/CT scans and X1 PET scans. The target lesions were located in the head & neck region, esophagus, mediastinum, abdomen, and pelvis. BgRT planning was unsuccessful for six patients due to either low activity concentration in the PTV or high FDG uptake in the PTV vicinity. BgRT plans were successfully generated for seven patients with an average GTV volume of 16.6±15.2 cm3 (range: 2.3 – 43.4 cm3) and an average PTV volume of 43.3±27.7 cm3 (range: 9.7 – 90.8 cm3). The BgRT plans had an average AC of 10.5±3.2 kBq/ml (range: 8.4 – 16.6 kBq/ml) and an average NTS of 9.1±4.9 (range: 3.4 – 16.0). The average estimated treatment time was 29.0±8.8 minutes (range: 13.4 – 41.2 minutes).
Conclusion: X1 PET scans on the BgRT machine allowed visualization of tumor metabolic activity at a variety of anatomical sites for treatment planning purposes. BgRT could potentially be delivered to non-bone and non-lung anatomical sites provided that sufficient FDG metabolic activity is demonstrated in the tumor.