Multicenter Validation of the Lattice Dose Fitness Index (LDFI): A Multi-Parameter Fusion-Based Comprehensive Evaluation Tool for Lattice Radiotherapy
Abstract
Purpose
Lattice radiotherapy (LRT) intentionally creates heterogeneous “peak-and-valley” dose distributions to improve therapeutic ratio in bulky tumors. Conventional plan-quality metrics fail to capture the multi-dimensional nature of LRT dose patterns. We propose and validate a novel Lattice Dose Fitness Index (LDFI) that integrates three complementary dosimetric dimensions for comprehensive LRT plan evaluation.
Methods
The LDFI integrates three core components: (1) Normal tissue sparing, measured by the integral dose ratio R1=ID_GTV/ID_GTV+2cm, where ID_GTV is the integral dose within the GTV and ID_GTV+2cm is the integral dose in a 2-cm expansion around the GTV; (2) Spatial ablation efficiency, represented by the volume ratio R2=V_LTV/V_GTV, where V_LTV is the total volume of high-dose lattice spheres and V_GTV is the gross tumor volume; (3) Dose conformity, quantified by the ratio of ideal to actual DVH curve areas R3=S_ideal /S_actual. The composite index is defined as: LDFI =α*R1+β*R2+γ*R3. where the normalization coefficients (α,β,γ) are independently derived from each center's clinical data, enabling center-specific calibration.
Results
Center-specific coefficients were successfully calibrated. At the primary center, using 25 simultaneous-boost LRT plans, coefficients were α=0.7786, β=20.0160, γ=0.4379, yielding a mean LDFI of 1.0023±0.146 (range 0.817-1.290). In a comparative study at a second center (n=19), Halcyon-based plans achieved a higher mean LDFI (1.01) than TrueBeam-based plans (0.99), consistent with expert qualitative judgment. The LDFI also proved effective in guiding plan optimization. For example, re-optimization of a plan with an initial LDFI of 1.0134 improved it to 1.2495, corresponding to visibly tighter isodose lines.
Conclusion
The LDFI is a robust, multi-parameter metric designed specifically for LRT plan evaluation. Its center-specific calibration accommodates institutional differences in planning strategy and equipment, while its quantitative output aligns with clinical judgment and effectively guides plan optimization, demonstrating strong potential for clinical standardization.