Dosimetric Comparison of Lattice Radiation Therapy Plans Using Varian C-Arm Linacs and Radixact Tomotherapy.
Abstract
Purpose
This study compares the dosimetric treatment plan quality of Lattice Radiation Therapy plans generated on Varian C-arm LINACs (TrueBeam and Edge) and Radixact TomoTherapy.
Methods
Twenty-five retrospective patients with tumors larger than 5 cm were selected, including lung/chest, liver, pelvis, and abdominal sites. LRT plans were created on Varian C-arm LINACs (TrueBeam and Edge) using Varian Eclipse v16.1 and on Radixact TomoTherapy using Accuray Precision v3.5.0.3. An identical lattice pattern of 1.5 cm diameter spheres with 3 cm center-to-center spacing was used. The spheres were placed within a contoured grid boundary inside the GTV, that had a 2 cm clearance from surrounding OARs. The clinical goal was 95% of the total spheres’ volume to receive 100% of the prescription dose; however, due to beam-on time limitations, all TomoTherapy plans were delivered in four fractions. Plan quality was evaluated using Conformity Index, Conformity Number, Gradient Index, Peak-To-Valley-Dose-Ratio, and Mean Dose to the grid spheres.
Results
All platforms showed similar prescription dose conformity. Mean CI was 1.04 for TrueBeam, 1.02 for Edge, and 1.01 for TomoTherapy. Mean CN values were also comparable, with TomoTherapy showing slightly higher values (0.89) compared to TrueBeam (0.87) and Edge (0.88). GI increased with increasing sphere number for all systems, with TomoTherapy showing lower mean GI (8.09) than Edge (9.37) and TrueBeam (10.23). Spatial dose modulation was higher for the C-arm LINACs, with mean PVDR of 5.47 for Edge and 4.83 for TrueBeam compared to 3.39 for TomoTherapy. Mean dose to the grid spheres was similar across platforms.
Conclusion
All systems produced acceptable LRT plans with comparable dose conformity. TomoTherapy showed slightly sharper dose falloff, while the C-arm LINACs achieved stronger spatial dose modulation. Platform selection may depend on whether high dose gradient or stronger spatial dose fractionation between high-dose peaks and low-dose valleys is prioritized.