Plan evaluation of four lattice SBRT layouts using existing and novel dosimetry metrics

Staykova, Vanya, Eaton, David J, Misson, Sarah and Kirby, Mike ORCID: 0000-0001-9765-5641 (2025) Plan evaluation of four lattice SBRT layouts using existing and novel dosimetry metrics [Poster]

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Description

Purpose/Objective Lattice radiotherapy (LRT) with regular geometric lattice layouts, has gained clinical and research attention due to better compatibility with automation in lattice creation and inverse planning [2, 3]. No definitive conclusions regarding optimum evaluation metrics, distribution pattern, and lattice geometries in LRT have been established, warranting further studies. This in silico study aims to evaluate heterogenous dose distributions in Lattice SBRT, using four different geometric lattice layouts applied to the same GTV across a patient cohort. Materials and methods: Four geometric lattice layouts with vertices’ diameter of 0.7, 1.0, 1.5, and 2.0cm (Table 1) have been investigated for large GTVs (867-1984cc) across five cases of various types tumours, following the planning and evaluation methodology of the LITE SABR M1 trial [2,4]. The prescribed doses were 66.70Gy to the high dose peaks-vertices (PTV_6670) and 20Gy to the rest of the GTV/PTV, in 5 fractions. Treatments plans were created with VARIAN Eclipse v15.6, HDMLC, RapidArc and Acuros-Dmed calculation algorithm, using 4 - 5 full or partial arcs. Results: The LRT plan evaluation metrics, as defined in previous studies [1-3], are presented in Table 1. The PTV_6670 median volume varies between 6.3 cc and 37.6 cc and ~1%-5% of the GTV, across the four layouts. The median of the mean doses of PTV_6670 and PTV_Avoid (the valley dose structures) and their ratio, DR, were similar across all four lattice layouts. The Peak-to-Valley-Dose-Ratio, PVDR= Dp/Dmean(100-95)% metric [1] showed a larger spread across the lattice layouts and the GTV volumes (Figure 1A). A new LRT metric “Lattice Rating Index”-LRI = PVDR/ (D50/Px doseGTV) was introduced and explored. The metric integrates PVDR and the GTV D50%, quantifying the desired steep dose gradient. Higher LRI values reflect a dose in “GTV-PTV_6670” closer to the Px valley dose, along with high PVDRs (Figure 1B, Table 1). The study found that layouts with a higher number of vertices exhibited lower PVDR and LRI values. The DR_1.5 metric (Dmedian/Dose_STD), presented in Table 1, demonstrated values larger than those previously reported [2], attributed to a smaller dose standard deviation in our study, while maintaining similar Dmedian values. Conclusions: Four diamond geometric lattice layouts with vertex diameters as small as 0.7 and 1.0 cm were successfully planned using RapidArc for five large tumours cases. The newly proposed “Lattice Rating Index” offers a promising metric for comprehensive evaluation of heterogeneous “peaks-and-valleys” dose distributions within GTVs in LRT.

Item Type:	Poster
Uncontrolled Keywords:	Lattice RT, SFRT, Treatment planning metrics
Divisions:	Faculty of Health & Life Sciences Faculty of Health & Life Sciences > Inst. Population Health
Depositing User:	Symplectic Admin
Date Deposited:	26 Sep 2025 08:21
Last Modified:	16 Jun 2026 19:53
DOI:	10.13140/RG.2.2.16221.32487
Related Websites:	Author
URI:	https://livrepository.liverpool.ac.uk/id/eprint/3194601
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