N. Roquet1, A. Beddok2, M. Loo3, G. Calais1, G. Crehange4, S. Chapet1, and T. Frédéric-Moreau3,5; 1CHRU de Tours - Centre Henry Kaplan - CORAD, Tours, France, 2Department of Radiation Oncology, Institut Godinot, Reims, France, 3Department of Radiation Oncology, Institut Curie, Saint-Cloud, France, 4Department of Radiation Oncology, Institut Curie, Paris, France, 5Centre doncologie et radiothérapie Saint-Jean, saint-doulchard, France
Purpose/Objective(s): To analyze outcomes and specific dosimetric impact on the occurrence of radionecrosis (RN) after hypofractionnated stereotactic radiotherapy (HSRT) of resected brain metastases (BMs). Materials/
Methods: We retrospectively evaluated 212 patients (pts) with BMs from lung (58.5%) and breast (41.5%) cancer treated from 2010 to 2023. 216 brain surgical cavities (SC) were treated with HSRT using either 3 (78.3%) or 5 (21.7%) fractions (F). Follow-up was realized by MRI every 3 months and RN was determined with specific MRI sequence of perfusion. The primary objective was to determine RN dosimetric factors. Secondary objectives included local control (LC) and radionecrosis pronostic factors (localization, size of SC and prescription dose). The median follow-up was estimated using the inverted Kaplan Meier method. Statistical analysis was conducted using Chi-square or Fishers exact tests for categorical data and Mann-Whitney U for continuous variables, setting the significance threshold at p<0.05. Results: After a median follow-up of 19 months (range 9-38), 34 (16.3%) pts had RN, 60% of which were symptomatic. Median BED10 was 51.3Gy (range 43.2-69.3) with a median prescription dose of 27Gy (range 18-33) in 3F and 30Gy (range 20-35) in 5F. Median SC volume was 7.7cc (range 1.2-53.7) in 3F group and 12.75cc (range 2.8-72.9) in 5F group. In the 3F group, V30Gy (p=0,033), V27Gy (p=0.006), V24Gy (p=0.007) and V21Gy (p=0.009) were significantly associated with RN. No dosimetric factor of RN was found in the 5F group. In the whole cohort, the 1-year and 2-year LC were 89.7% and 80.4% respectively. A delay from 5 to 9 weeks between surgery and radiotherapy (p=.048) and BED10 = 48 Gy (p=0.041) were associated with better LC. Conclusion: This large multicenter retrospective study shows significant dosimetric factors on the occurrence of RN in the specific situation of resected BMs patients treated by HSRT. BED10 and delay between surgery and radiotherapy have a significant impact on LC.
