Evaluation of Lattice Radiotherapy Feasibility on Elekta Versahd and Varian Ethos Platforms
Abstract
Purpose
Lattice radiotherapy (LRT) is a spatially fractionated radiation therapy technique in which high‑dose vertices are delivered within a gross tumor volume while maintaining lower‑dose valley regions. The technique requires reliable dose modulation and clinically practical delivery. This study evaluates the feasibility of planning and delivering lattice radiotherapy on the Elekta VersaHD and Varian Ethos platforms using a common treatment planning system.
Methods
Four patients previously treated with VMAT were retrospectively selected. For each patient, three lattice radiotherapy plans were generated in Eclipse (Varian Medical Systems), resulting in twelve plans total. Plans included Ethos 6 MV flattening‑filter‑free (6FFF), VersaHD 6 MV (6X), and VersaHD 6 MV FFF beam models. All plans were prescribed 15 Gy delivered in a single fraction. Lattice boost structures consisted of 1 cm diameter spherical vertices arranged in a three‑dimensional hexagonal pattern with 3 cm center‑to‑center spacing. Only full spheres entirely contained within the gross tumor volume were included, and lattice geometry was identical across all plans. Each plan used four full coplanar VMAT arcs with collimator angles of 0°, 30°, 90°, and 330°. Optimization objectives targeted vertex maximum doses between 125% and 150% of prescription and a peak‑to‑valley ratio (PVR) below 0.4. Plans were evaluated based on achieved PVR, vertex dose escalation, and monitor units.
Results
All plans met predefined lattice objectives. Achieved PVR values ranged from 0.2 to 0.4, with vertex maximum doses within the intended range. VersaHD plans required up to 40% fewer monitor units than Ethos 6FFF plans while maintaining comparable lattice dose distributions.
Conclusion
Lattice radiotherapy prescribed to 15 Gy in a single fraction can be planned in Eclipse and delivered on both the Elekta VersaHD and Varian Ethos using standard VMAT techniques. Both systems produced consistent lattice geometry and acceptable spatial dose modulation, supporting their clinical feasibility for lattice radiotherapy.