2633 - Temporal Lobe Radionecrosis after Proton Beam Radiation in Patients with Skull Base Chordoma
Presenter(s)
H. Mammar1, A. Bonfrate1, Y. Khattabi1, C. Cheptea1, S. Alali1, P. Loap1, E. Jouglar1, E. Le Reun2, S. Froelich3, T. Passeri3, N. François3, R. Abriti3, D. Ricard4, F. Goudjil5, I. Pasquie1, J. Jacob6, L. Feuvret7, V. Calugaru5, S. Helfre1, L. De Marzi5, and R. Dendale5; 1Department of Radiation Oncology-Institut Curie, Paris, France, 2Institut Curie, Paris, France, 3Department of Neurosurgery - Lariboisière Hospital Paris - France, Paris, France, 4Departement Neurology Hôpital Percy, Clamart, France, 5Department of Radiation Oncology, Institut Curie, Paris, France, 6University Hospitals Pitié-Salpêtrière, Paris, France, 7Department of Radiation Oncology, Hôpital Pitié-Salpêtrière Charles Foix, APHP, Paris, France
Purpose/Objective(s):
High-dose proton therapy has improved the local control rate of chordomas of the skull base but also increased the incidence of radionecrosis in the temporal lobes. A dosiomics has allowed us to accurately assess the actual dose received at the necrosis points. We present the correlation between imaging changes in brain normal tissue and the spatial distribution of linear energy transfer (LET), and the patients outcomes treated between 2012 and 2023 in Institut Curie, FranceMaterials/Methods:
185 consecutive patients with skull base chordoma (median age 54 yo at the time of RT, range 22-75) were treated with proton therapy (PT) between 2012 and 2023. The median dose delivered was 73.8 GyE (range 68.4-73.8) after gross tumor resection. The female/male ratio was 13/17. Out of all these patients, 30 patients (16%) developed a radionecrosis following their treatment. Twenty-four patients developed temporal RN [Bi-Temporal lobe (n=10); Temporal Lobe right (n=6); and Left Temporal Lobe (n=8)]. Twenty-Seven patients were treated by double scattering technique (DS) and 3 patients by pencil beam scattering (PBS). For each patient, dose-averaged LET (LETd) distributions were computed using the TOPAS/Geant 4 Monte Carlo code. The variable Relative Biological Effectiveness (RBE) was also assessed thanks to the McNamara model. For comparison, a cohort of only 60 patients without RN was built. The RBE-weighted dose in the necrosis area was compared between patients with and without RN. No patient had a genetic disorder predisposing to increased radiosensitivityResults:
The analysis of the RN showed a preferential location in the PTV margin located in the temporal lobes. The variable RBE-weighted dose within the RN increased by 7-10 Gy compared to the biological dose with a RBE of 1.1. the average time to onset of RN was 22 months. The comparison between the two cohorts did not show any differences in terms of RBE-weighted dose and LETd. Only one patient developed radionecrosis > grade 2 (CTCAE v5.0)Conclusion:
High-dose conformal PT is safe and effective in SBC in close proximity with the temporal lobe with minimal neurotoxicity. No clear correlation between the RN and the physical parameters was found