Treating patients with real-time tumor tracking using the Vero gimbaled linac system: implementation and first review.
This retrospective study explored 2-[18F]fluoro-2-deoxy-D-glucose positron emission tomography (FDG-PET) as an aid in target delineation among a first-group of five patients with single or multiple moving lung tumors planned for Vero stereotactic body radiation therapy (SBRT). Computed tomography (CT)-based free-breathing, end-inspiration, and end-expiration lung target volumes generated a single internal target volume (ITV). ITVs were compared to a thresholded 40% maximum standard uptake value FDG-PET target volume (CTVpet), a contour assumed to be a surrogate for lung target motion during quiet breathing. Planning target volumes (PTV) and relevant lung planning constraints determined clinical execution of Vero SBRT. A mean 28% PTV expansion by adding in a CTVpet contour to the CT-based ITV converted two (40%) of five cases from SBRT fractionation (40 Gy in four every other day fractions) to conventional fractionation (30 Gy in ten daily fractions). In all five cases, CTVpet contours captured target motion not enclosed by the CT-based ITV. Vero SBRT radiation plans achieved effective normal tissue sparing without compromise of PTV target coverage. A single instance of less than 30-day posttherapy grade 2 fatigue occurred; no pulmonary toxicity has been observed in the 3-month follow-up period. Thresholded CTVpet contours impacted target delineation and clinical delivery of Vero SBRT treatment.