S1874
Physics - Dose prediction/calculation, optimisation and applications for photon and electron planning
ESTRO 2026
Digital Poster 2121
Evaluating multi-target beam setup for LINAC- based stereotactic treatment of multiple brain metastases with individual dose prescriptions. Xander R. Staal 1 , Jaap D. Zindler 2,3 , Anna L. Petoukhova 1 1 Medical Physics, Haaglanden MC, Leidschendam, Netherlands. 2 Radiation oncology, Haaglanden MC, Leidschendam, Netherlands. 3 Radiation oncology, HollandPTC, Delft, Netherlands Purpose/Objective: In LINAC-based single isocenter non-coplanar stereotactic treatment of multiple brain metastases (BMs), beams can be assigned to treat only a subset of the metastases. This is an effective way to minimise island blocking and improve plan quality while maintaining time-efficient treatments [1]. RayStation multi-target beam setup (MTBS) automates the process of beam setup, partitioning BMs into subsets and assigning them to the available beams. We evaluated the effectiveness of MTBS for treating multiple BMs with individual dose prescriptions. Material/Methods: Ten anonymised patients, with 5 to 20 BMs (median=12), were selected for this treatment planning study. All these patients had BMs less than 4 cm in diameter and a Karnofsky score of at least 70. Within any treatment plan, each BM was separately prescribed a dose based on the volume of its PTV, leading to multiple prescription doses per plan.For each patient four treatment plans were optimised from scratch, with each plan using a different method to partition BMs and assign them to beams:Manual beam setup by an RTTScripted beam setup following a simple algorithmMTBS-A: using a number of available beams according to protocolMTBS-B: allowing a larger number of available beamsPlan quality parameters were extracted from each plan, including the volume of the healthy brain (brain-GTV) receiving 5 Gy (V5Gy) and 12 Gy (V12Gy), a conformity index (CI) and gradient index (GI). Plan quality parameters from plans from methods 2-4 were compared to those from method 1 using the Wilcoxon signed-rank test. Results: Figure 1 shows an example dose distribution from patient 7.
Based on the statistical analysis (table 1), scripted beam setup gave no clear improvement or degradation compared to the manual beam setup. MTBS-A slightly outperformed manual beam setup, but these results were not statistically significant. MTBS-B outperformed manual beam setup significantly, at the cost of increased treatment time.
Conclusion: MTBS is a useful tool for setting up non-coplanar LINAC-based stereotactic treatment plans of multiple brain metastases with individual dose prescriptions. When using the same number of beams, we do not expect MTBS to give a significant improvement in plan quality compared to manual beam setup. However, it will save RTTs a significant amount of time on beam setup, especially as the number of metastases and beams in the plan increases. References: 1. Sundström J, Finnson A, Hynning E, De Kerf G, Fredriksson A. Partitioning of multiple brain metastases improves dose gradients in single- isocenter radiosurgery. Med Phys. 2025;52(10):e18117. doi:10.1002/mp.18117 Keywords: Stereotactic, beam setup, brain metastases
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