ESTRO 2025 - Abstract Book

S743

Clinical - CNS

ESTRO 2025

since primary radiotherapy. Tumor volume (GTV) ranged from 3.5 to 20.2 cm 3 and most tumors (60%) were located in the left frontal lobe. Fractionation was as follows: 16 Gy in 2 fractions in 43 patients, 10 Gy in 2 fractions in 21 patients, 12 Gy in 2 fractions in 14 patients. Results: Follow-up was 4-36 months. Progression-free survival in our group was 3-24 months (median 8 months). Six months after the completion of CyberKnife radiotherapy 14 patients (17.9%) showed partial tumor regression. During and shortly after radiotherapy 65% of patients reported moderate headache (CTCAE grade 1-2), 29% reported mild nausea (CTCAE grade 1). No severe toxicity was observed.

Conclusion: In our experience, CyberKnife ® stereotactic radiation therapy is a valuable treatment option for recurrent glioblastoma, offering good efficacy combined with low toxicity level.

Keywords: CyberKnife, high grade glioma, HGG recurrence

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Digital Poster Is dose escalation necessary for patients with glioblastoma who are to be treated with radiotherapy? A single-institutional descriptive analysis. Alba G. Curbelo Artiles 1 , Esther Mayrata Cañellas 1 , Marc Alomar Payeras 2 , Francesc J. Mestre Mestre 1 1 Department of Radiation Oncology, Hospital Universitario Son Espases, Palma de Mallorca, Spain. 2 Department of Medical Physics, Hospital Universitario Son Espases, Palma de Mallorca, Spain Purpose/Objective: Radiotherapy is a core treatment modality in the management of glioblastomas. However, the relapse rate often seen in such patients after completing standard treatment is striking, where the optimal treatment volume is still a matter of debate. The current analysis was aimed to determine the pattern of recurrence with reference to the initial PTV and GTV in patients with glioblastomas treated with radiotherapy while taking into account different parameters such as type of surgery, molecular biomarkers or concomitant temozolamide cycles. Material/Methods: Between July 2019 and May 2024, 51 recurrent patients with GBM were retrospectively assessed. The site of local relapse on magnetic resonance imaging (MRI) was related to the PTV (inside, outside, partial) and if the recurrence was within PTV, we related it with respect to GTV (inside, outside or partial), with the help of the Varian and Monaco Treatment Planning System. The dose received by the site of recurrence was investigated. Results: The sample studied consisted of a total of 51 patients, including 33 males (64.7%) and 18 females (35.3%). The median age of these patients was 58 years (range 52-65). On the other hand, the most prevalent symptoms at recurrence were: headache (27.7%), seizures (19.1%), and instability (17%), however, 36.2% of the sample was asymptomatic. Regarding the fractionation scheme used, only 6 patients in the sample received a hypofractionated treatment due to the baseline condition of these patients. Regarding the analysis of relapses, 34 patients (66.7%) relapsed within the PTV, 16 (31.4%) relapsed partially and only 1 patient (2%) relapsed outside the PTV. Of those who relapsed within the PTV, 85% of the sample relapsed completely outside the GTV, or partially overlapped with it. It should be noted that we found no statistically significant differences with respect to the type of surgery performed (partial or complete exeresis) or the biomolecular markers (IDH, MGMT methylation and EGFR amplification). Finally, it is worth mentioning that the