S386
Clinical - CNS
ESTRO 2026
4.5 months (range: 3-7.5). During follow-up, most patients were able to taper or maintain their steroid dose. No serious adverse events were observed, and no symptomatic radiation necrosis was detected. Median OS and PFS after LRT were 5.9 months (95% CI: 3–9) and 4.7 months (95% CI: 3–7), respectively. A trend toward better PFS was observed among individuals with an RT2-LRT interval of ≥ 12 months (p=0.08) and a LRT GTV volume of ≤ 200 cm ³ (p=0.06). Furthermore, the response to RT2 significantly influenced OS and PFS (p=0.03). Additionally, tapering or maintaining the steroid dosage during the first month notably enhances OS and PFS (p=0.002). Figure 1 presents the MR images along with the Lattice design of one of the patients. Regarding systemic treatment, they received various regimens; one patient who received pembrolizumab achieved a complete response and has maintained it for 6.5 months after treatment.
clinical trials: Global Harmonization Group consensus guidelines. Radiother Oncol 2020;150:30– 9. https://doi.org/10.1016/J.RADONC.2020.05.0382. Milano MT, Grimm J, Niemierko A, Soltys SG, Moiseenko V, Redmond KJ, et al. Single- and multifraction stereotactic radiosurgery dose/volume tolerances of the brain. Int J Radiat Oncol Biol Phys 2021;110(1):68e86. https://doi.org/10.1016/j.ijrobp.2020.08.013 Keywords: SRS, contouring, quality assurance Digital Poster 3871 Robotic gyroscopic lattice radiotherapy for recurrent or progressive high-grade gliomas: The largest secondary re-irradiation cohort to date Sepideh Mohammadipour 1 , Gozde Yazici 1 , Fazli Yagiz Yedekci 1 , Melek Tugce Yilmaz 1 , Huseyin Kivanc 1 , Gokcen Coban Cifci 2 , Neyran Kertmen 3 1 Department of Radiation Oncology, Hacettepe University Faculty of Medicine, Ankara, Turkey. 2 Department of Radiology, Hacettepe University Faculty of Medicine, Ankara, Turkey. 3 Department of Medical Oncology, Hacettepe University Faculty of Medicine, Ankara, Turkey Purpose/Objective: Lattice Radiation Therapy (LRT) is a new technique delivering high doses to large, resistant tumors like high-grade gliomas (HGG), protecting nearby organs and boosting immune response. This study aimed to assess the safety, feasibility, and outcomes of LRT in patients with recurrent or progressive HGG. Material/Methods: Patients who had undergone at least two previous radiotherapy sessions (RT1 and RT2) were enrolled in this prospective observational single-center study. Treatments were performed via the ZAP-X® gyroscopic radiosurgery platform (ZAP Surgical Systems, Inc., San Carlos, USA). The lattice geometry was created with custom Python software to generate patient-specific 20 Gy vertices within the GTV, aiming for a mean dose over 5 Gy. GTV included all Fluid- Attenuated Inversion Recovery changes observed on the planning MRI. All patients received single-fraction LRT and underwent follow-up evaluations at months 1 and 3. For those not on steroids before, 4 mg/day oral dexamethasone was started, and all were instructed to taper their steroid doses within two weeks. Kaplan- Meier analyses were conducted to assess overall survival (OS) and progression-free survival (PFS), as well as prognostic factors. Results: Between December 2024 and August 2025, 11 patients were included. Patients and treatment characteristics are summarized in Table 1. The median follow-up was
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