S959
Clinical - Non-malignant & functional radiotherapy
ESTRO 2026
assessment of treatment efficacy may be complicated by temporary post-treatment volume increases known as pseudoprogression. The definition of pseudoprogression varies, most often describing a transient lesion volume increase of 10–20%, followed by regression within a 24–36-month period. Material/Methods: We performed a volumetric analysis of 87 vestibular schwannomas treated with the CyberKnife robotic radiosurgery system. The median initial tumour volume was 1.11 cm ³ (range 0.05–12.05; IQR 0.41– 2.18). Treatment was delivered in a single fraction in 57 cases (65.5%), in three fractions in 24 (27.6%), and in five fractions in 6 (6.9%). The most frequently prescribed doses were 12 Gy (range 12–14), 18 Gy (range 18–21), and 25 Gy (range 22.5–27.5), respectively. Follow-up ranged from 6.1 to 106.9 months (median 44.6; IQR 18.2–64.3); 51 cases (58.6%) had follow-up > 36 months. Contrast-enhanced MRI scans were imported into Precision™ planning system (Accuray, Sunnyvale, CA, USA), contoured, and recorded in a dedicated REDCap database hosted by the Riga Stradins University Laboratory of Statistics. Statistical analysis was performed in Microsoft Excel (version 2510; Microsoft Corporation, Redmond, WA, USA). Results: At last follow-up, 55 lesions (63.2%) had decreased in volume and 2 (2.3%) were stable. The remaining cases had follow-up < 36 months or showed volume increase at last follow-up, being considered potential relapses (Diagram 1).
follow-up period of two years and included the evaluation of severe or worse (CTCAE grade ≥ 3) adverse events (AEs) and the evaluation of treated VT episodes (excluding a 6-week blanking period), respectively. Results:
Seven patients were included in this study (all male, age 54-83). All had ischemic cardiomyopathy (left ventricular ejection fraction 17-52%) and the median number of VT ablations before STAR was 1 (0-5). During follow-up, two patients died because of non- treatment related, non-cardiac causes (7 and 11 months; cross in Figure 1). Three severe possibly, probably or definitely treatment-related AEs were observed, all in one patient (chest-wall pain, bronchopulmonary hemorrhage and cardiac chest- pain at 4, 21 and 22 months after treatment, respectively). Two year efficacy results are shown in Figure 1. Three patients underwent one (P4 and P5) or two (P7) VT ablation(s) after STAR (bullseye in Figure 1). Conclusion: In this middle-term follow-up study, severe treatment- related AEs were scarce and manageable. Although VT recurrences were common in some patients, new VT ablations were feasible in these earlier therapy- refractory VT patients. Keywords: STAR, Stereotactic Arrhythmia Radiotherapy, VT Volumetric analysis of Vestibular Schwannoma after Cyberknife Stereotactic Radiosurgery/SBRT: single center study Maris Mezeckis 1 , Elizabete Stankevica 2 , Karina Anete Mazjane 2 , Vladyslav Buryk 1 , Maris Skromanis 1 , Igors Aksiks 3 , Galina Boka 1 , Indra Surkova 1 1 Radiosurgery Centre Sigulda, Sigulda Hospital, Sigulda, Latvia. 2 Faculty of Medicine, University of Latvia, Riga, Latvia. 3 Department of Surgery, Riga 1. hospital, Riga, Latvia Purpose/Objective: CyberKnife SRS/SBRT is an effective alternative to microsurgery for vestibular schwannoma; however, Digital Poster 5060
For the 57 lesions showing volume reduction or stability, the median absolute volume decrease was 0.6 cm ³ (range 0–6.9; IQR 0.3–1.2), corresponding to a median relative reduction of 42.2% (range 0–82; IQR 20.7–62). Transient tumour volume increase with subsequent regression below baseline (pseudoprogression) was observed in 22 lesions (38.6%). The median absolute increase was 0.42 cm ³ (range 0.05–1.53; IQR 0.18–0.72), and the median relative increase was 24.8% (range 3.4–130.8; IQR 10.9–41.1). Only one pseudoprogression episode began beyond 36 months after treatment. The median duration of pseudoprogression was 16.5 months
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