Impact of Number and Placement of High-dose Vertices on Equivalent Uniform Dose and Peak-to-valley Ratio for Lattice Radiotherapy

This study evaluated the influence of high dose (HD) vertex numbers and its placement on equivalent uniform dose (EUD) and peak-to-valley dose ratio (PVDR) in lattice radiotherapy (LRT). One hundred and eighty-eight RapidArc (RA) plans were created for a cohort of 15 patients. RA plans were created with zero to eight HD vertices to analyze their relationship with EUD. Eight lattices were systematically and optimally placed (by avoiding proximity to organs at risks [OARs]) to study the impact of vertex placement. Variations in PVDR were assessed using PVDR1 (mean dose to HD vertices by the difference of mean doses to planning target volume [PTV] and HD vertices) and PVDR2 (D10/D90 of PTV in composite plans) across 38 RA plans with HD vertex doses of 9 Gy, 12 Gy, 15 Gy, and 18 Gy. PVDR3 (product of PVDR1 and PVDR2) was evaluated for its variation with peak dose. Hypothesis testing between vertex placements was performed using a two-tailed Student's t-test. EUD values ranged from 32.88 Gy to 40.63 Gy. In addition, statistical analysis revealed significant associations (P = 0.0074) between the placement patterns of HD vertices, both in systematic and optimized arrangements. The PVDR and D10/D90 product values were 1.6, 1.8, 2.1, and 2.3 for peak doses of 9 Gy, 12 Gy, 15 Gy, and 18 Gy, respectively. The addition of one HD vertex increased EUD, emphasizing the impact of individual vertex increments on outcomes. Systematic and optimized vertex placements enhance EUD, with optimized placement yielding better doses to PTV and OARs. PVDR3 offers superior dose reporting for LRT compared to PVDR1 and PVDR2.