Dosimetric comparison between ring_gantry and c_arm modalities for lattice radiotherapy in large-volume tumors across different anatomical sites.

Abstract

PurposeThis study evaluates the feasibility, dosimetric optimization, and delivery efficiency of c_arm linac-based and TomoTherapy-based Lattice Radiotherapy (LRT) across head and neck, thoracic, and abdominal tumors.Materials and methods72 patients meeting inclusion criteria (GTV > 480 cc, at least eight lattice vertices) were planned with both VMAT and Helical techniques. Each high-dose lattice received 60 Gy in five fractions. Identical lattice geometries and concentric valley dose rings were applied for both systems. VMAT plans utilized four partial arcs, while helical plans employed helical delivery with a 2.5 cm field width to assess the impact on dose modulation. Key dosimetric indices (GTV D95%, Dmean, D50%, Homogeneity Index, Peak-to-Valley Dose Ratio, and spatial dose modulation metrics) were calculated. An anthropomorphic phantom with OSLDs and ArcCHECK was used for independent validation.ResultsBoth platforms achieved the intended spatially fractionated dose distribution with adequate vertex coverage. c_arm plans demonstrated significantly higher peak doses (D2%) and PVDR, indicating stronger peak-valley modulation. ring_gantry plans showed higher D95% and D98%, reflecting increased low-dose GTV coverage and smoother intratumoral dose redistribution, whereas c_arm plans showed higher PVDR, indicating sharper peak-valley modulation. Beam-on time was substantially shorter for c_arm (3-5 min) compared to ring_gantry (20-31 min, p ConclusionBoth platforms generated acceptable LRT dose distributions with distinct platform-level dosimetric characteristics. c_arm plans produced sharper peak-valley modulation and shorter beam-on times, whereas ring_gantry plans showed smoother intratumoral dose redistribution, modest reductions in selected OAR dose metrics, and slightly higher gamma agreement under the evaluated QA criteria.