GRID-Lattice: A Compact and Robust Proton Lattice Strategy Using a GRID Entrance Beam Pattern
Abstract
Purpose
Proton LATTICE radiotherapy (LRT), a spatially fractionated radiotherapy (SFRT), delivers high dose to intratumoral vertices while maintaining low valley dose. Single-field optimization (SFO) is robust in preserving peak-to-valley patterns but may increase entrance dose. We propose proton GRID-LATTICE, which reshapes an SFO LATTICE field into narrow GRID-like entrance beamlets to redistribute entrance dose while preserving vertex coverage and robustness.
Methods
A semi-FCC, geometry-constrained optimization generated non-overlapping vertices (4.4-mm diameter; minimum spacing 1.4±0.2 cm) and mapped them to deliverable GRID beamlets under spacing/clearance constraints. A fixed beam-eye-view GRID pattern (1.0-cm spacing; 5-mm openings) was used. Eight deep-inspiration breath-hold primary liver cancer cases were replanned in RayStation v2023B with SFO (18 Gy/vertex,3 Gy/GTV). Endpoints included GTV D95%, GTV Dmean, gEUD (a=−10), PVDR, skin D1%, and liver–GTV Dmean. Robustness (±3.5% range,±5 mm setup;14 scenarios) was summarized by second worst-case values, with CBCT-based evaluations assessing stability over the treatment course.
Results
Nominal plans achieved PVDR 3.6±0.4 (≥3.5), GTV D95% 3.1±0.08 Gy, GTV Dmean 5.8±0.6 Gy, gEUD 3.5±0.1 Gy, liver–GTV Dmean 0.9±0.3 Gy, and skin D1%1.4±0.6 Gy. PVDR decreased to 3.3±0.4 in the robust second-worst case (p<0.05), with 1.7%, 5.8%, and 2.8% average changes in GTV D95%, Dmean, and gEUD (p<0.05). CBCT evaluation preserved PVDR (3.6±0.6 first; 3.5±0.6 last) without meaningful degradation in other metrics.
Conclusion
GRID-LATTICE is a compact, robust, and clinically feasible proton LRT delivery strategy that maintains robust spatial fractionation under treatment uncertainty and anatomical variation, supporting broader proton SFRT applicability when entrance dose is limited. This compact approach may extend SFRT to more patients, including those with smaller or difficult-to-treat targets.