ESTRO 2023 - Abstract Book

S924

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ESTRO 2023

Conclusion Fractionated stereotactic radiotherapy for ONSM yields positive results for VA and VF in patients with a good vision at the start of the treatment. Therefore, starting radiotherapy before severe VA loss occurs, could be beneficial to preserve visual function. The change in appearance due to exophthalmos was a serious QoL impairment.

PO-1154 Impact of dosimetric parameters on local control in stereotactic radiotherapy of brain metastases

C. Berthet 1 , F. Lucia 2 , V. Bourbonne 2 , U. Schick 2 , I. Lecouillard 1 , C. Le Deroff 1 , A. Barateau 1 , R. De Crevoisier 1 , J. Castelli 1

1 Centre Eugène Marquis, Radiation oncology, Rennes, France; 2 CHRU, Radiation oncology, Brest, France

Purpose or Objective Stereotactic radiotherapy for brain metastases (BM) allows very good local control (LC). However, approximately 20 to 30% of these lesions will recur. The objective of this retrospective study was to evaluate the impact of dosimetric parameters on LC in cerebral stereotactic radiotherapy. Materials and Methods Patients treated with stereotactic radiotherapy for 1–3 BM between January 2015 and December 2018 at two French centers were retrospectively included. A total of 349 patients with 538 lesions were included. The median gross tumor volume (GTV) was 2 cm3 (IQR, 0–7). The median biological effective dose with α / β =10 (BED10) was 60 Gy (IQR, 32–82). The median prescription isodose was 71% (IQR, 70–80). Clinical and dosimetric data were obtained. Correlations with LC were examined using the Cox regression model. Results The median follow-up period was 55 months (min-max, 7–85). Median overall survival was 17.8 months (IQR, 15.2–21.9). Of the 539 lesions, there were 95 recurrences and LC at 1 and 2 years was 87.1% (95% CI, 84–90) and 78.1% (95% CI, 73.9–82.4), respectively. Univariate analysis showed that systemic treatment, dose to 2% and 50% of the planning target volume (PTV), BED10 > 50 Gy, and low PTV and GTV volume were significantly correlated with better LC. In the multivariate analysis, GTV volume, prescription isodose, and BED10 were significantly associated with LC. Conclusion These results show the importance of a BED10 > 50 Gy associated with a prescription isodose <80% to optimize LC during stereotactic radiotherapy for BM.

PO-1155 Distribution and failure patterns of primary central nervous system lymphoma related to hippocampus