The Stanford Volumetric Modulated Arc Therapy Total Body Irradiation Technique

In this article, we describe the technical aspects of the Stanford volumetric modulated arc therapy (VMAT) total body irradiation (TBI) technique, compare it with other VMAT-TBI techniques, and share our initial experience.

From September 2019 to August 2021, 35 patients were treated with VMAT-TBI at our institution. Treatment planning was performed using in-house developed automated planning scripts. Organ sparing depended on the regimen: myeloablative (lungs, kidneys, and lenses) and nonmyeloablative with benign disease (lungs, kidneys, lenses, gonads, brain, and thyroid). Quality assurance was performed using electronic portal imaging device portal dosimetry and Mobius3D. Robustness was evaluated for the first 10 patients by performing local and global isocenter shifts of 5 mm. Treatment was delivered using image-guided radiation therapy for every isocenter and every fraction. In vivo measurements were performed on the match line between the VMAT and anterior-posterior/posterior-anterior fields and on the testes for the first fraction.

The lungs, lungs - 1 cm, and kidneys D_mean were consistently spared to 57.6% ± 4.4%, 40.7% ± 5.5%, and 70.0% ± 9.9% of the prescription dose, respectively. Gonadal sparing (D_mean = 0.69 ± 0.13 Gy) was performed for all patients with benign disease. The average planning target volume (PTV) maximum dose to 1 cubic centimeter (D_1cc) was 120.7% ± 6.4% for all patients. The average Gamma passing rate for the VMAT plans was 98.1% ± 1.6% (criterion of 3%/2 mm). Minimal differences were observed between Mobius3D- and Eclipse AAA-calculated PTV D_mean (0.0% ± 0.3%) and lungs D_mean (-2.5% ± 1.2%). Robustness evaluation showed that the PTV D_max and lungs D_mean were insensitive to small positioning deviations between the VMAT isocenters (1.1% ± 2.4% and 1.2% ± 1.0%, respectively). The average match-line dose measurement indicated patient setup was reproducible (96.1% ± 4.5% relative to prescription dose). Treatment time, including patient setup and beam-on, was 47.5 ± 9.5 min.

The Stanford VMAT-TBI technique, from simulation to treatment delivery, was presented and compared with other VMAT-TBI techniques. Together with publicly shared autoplanning scripts, our technique may provide the gateway for wider adaptation of this technology and the possibility of multi-institutional studies in the cooperative group setting.