Spot-Scanning Proton Arc Therapy for Lattice Radiotherapy

Document Type

Conference Proceeding

Publication Date

6-2024

Publication Title

International Journal of Particle Therapy

Abstract

Background and aims: Herein we introduce a spot-scanning proton arc (SPArc) approach to spatially-fractionated ("lattice") radiotherapy. Methods: Lattice plans were generated for 10 large tumors using single-arc SPArc and 4-field intensity modulated proton therapy (IMPT) for an IBA ProteusONE benchmarked against a dual-arc volumetric modulated arc therapy (VMAT) technique. Lattice geometries were standardized and algorithmically generated to comply with Washington University in St. Louis’s existing protocol (doi.org/ 10.1016/j.adro.2020.100639): vertices were 1.5 cm in diameter and arrayed in a body-centered cubic lattice with a 6 cm period. Vertices were clipped within 0.5 cm of the target border or 1.5 cm of a critical Organ-At-Risk (OAR). The prescription dose was 20 Gy(RBE) in 5 fractions to the tumor periphery; vertices received a simultaneous integrated boost to 66.7 Gy(RBE). OAR constraints per AAPM TG101 were prioritized. Dose Volume Histograms (DVH) were extracted and used to identify maximum, minimum, and mean doses; equivalent uniform dose (EUD); D95%, D50%, D10%, D5%; V19Gy; peak-to-valley dose ratio (PVDR); and gradient index (GI). The Wilcoxon signed-rank test was used to compare PVDR and GI between techniques as well as perform dose-wise comparisons between DVH (α=0.05). Results: Table 1 summarizes the results. Median tumor volume was 519 cc with a median of 4 high-dose vertices per plan. Figure 1 shows a representative tumor with plans from each technique and a line dose comparison. Low dose coverage was maintained in all plans (median V19Gy: SPArc 96%, IMPT 95%, VMAT 93%). SPArc generated significantly greater dose gradients as measured by median PVDR (SPArc 4.3, IMPT 4.0, VMAT 3.9; SPArc–IMPT p=0.002, SPArc–VMAT p=0.049) and median high-dose GI (SPArc 6.9, IMPT 9.6, VMAT 12.3; SPArc–IMPT p=0.002, SPArc–VMAT p=0.006). OAR constraints were met in all plans. Figure 2 shows DVH information exhibiting a significant dosimetric advantage over VMAT (17–42 Gy, 71–86.5 Gy) and IMPT (20.5–36 Gy, 66–102.5 Gy). Conclusion: SPArc therapy achieved high-quality lattice plans with superior PVDR and GI for various disease sites compared to IMPT and VMAT. Future development of the SPArc-LATTICE technique is warranted for clinical implementation.

Volume

12

Issue

Suppl

First Page

189

Comments

62nd Annual Conference of the Particle Therapy Cooperative Group (PTCOG), June 10-15, 2024, Singapore

DOI

10.1016/j.ijpt.2024.100535

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