ESTRO 2025 - Abstract Book

S673

Clinical - CNS

ESTRO 2025

1462

Digital Poster Refining optic neuropathy in patients undergoing pencil beam scanning proton therapy Juliette Thariat 1 , nathan azemar 2 , mathieu seraphim 1 , jean claude quintyn 3 , thao nguyen pham 1 1 radiation oncology, centre baclesse, caen, France. 2 GRami, LPC UMR6534, caen, France. 3 ophtalmology, university hospital, caen, France Purpose/Objective: The predictive power of the Lyman-Kutcher-Burman and Poisson models is poor for radiation-induced optic neuropathy (RION) following radiation therapy by pencil beam scanning proton beams (Köthe IJROBP-2020). Using systematic high-throughput paraclinical ophthalmological data (Tamplin Sci rep 2024) collected prospectively in consecutive patients with brain/head and neck/skull-base tumors, we aim to assess low to severe grades (G) of toxicities, perform voxel-based analysis of RION and to enrich predictive models with mechanistic insights. Material/Methods: RION was graded using the Common Toxicity Criteria (CTCVAEv5) definition derived from visual acuity graded using Monnoyer’s scale (from ETDRS conversion) in patients treated with PBS. Visual perimetry provided global and sectorial mean deficit (MD), and field amputation was graded (by 3dB incremental deficit differences to G4 worse than -12dB). G4 RION NTCP model used Dmax to the optic nerves, employing a probit dose-response function. We assessed temporal and spatial relationships between visual acuity and field loss with morphological and functional optic nerve damage and dose to functional optic substructures. Ganglion cell atrophy and retinal nerve fiber layer (RNFL) on macular and papillary optical coherence tomography (OCT) and optic nerve demyelination by visual evoked potentials and dosiomics were collected to provide additional spatial dose-volume insights Results: Of 240 patients, 33.4% (including 14.2% G3-4) has some degree of visual alteration before radiotherapy; over 50% were heavily-pretreated, with at least one surgery. With median follow-up of 23.2 months, G0-2, G3 or G4 visual acuity deterioration was detected in 81%, 14%, and 5% (with 12 patients experiencing bilateral G4) of patients (14 with a meningioma) at their last follow-up. Corresponding G0-2, G3, G4 visual field amputation rates were 79%, 10%, and 11%, respectively. Max dose causing RION in 50% of patients in this cohort was 51.9 Gy. There was a significant correlation between visual acuity and field at baseline but not follow-up (R=-0.49, p<0.001; R=-018, p=0.18), suggesting that some patients without acuity loss have field amputation, a symptom not captured by the CTCVAEv5 system. Significant correlation was noted between visual acuity and nerve fiber atrophy on RNFL at baseline and follow-up (with some outliers) (R=-0.28, p=0.05; R=-0.31, p=0.02). Conclusion: Systematic analysis using paraclinical ophthalmologic examinations suggests that the incidence of severe RION is higher than previously reported. The CTCVAEv5 does not appropriately qualify G1-2 RION. The dose metrics may need refinements based on patient history and tumor location. Analyses of ophthalmologic data and physical parameters are being integrated in multivariable models References: Köthe A, van Luijk P, Safai S, Kountouri M, Lomax AJ, Weber DC, Fattori G. Combining Clinical and Dosimetric Features in a PBS Proton Therapy Cohort to Develop a NTCP Model for Radiation-Induced Optic Neuropathy. Int J Radiat Oncol Biol Phys. 2021 Jun 1;110(2):587-595. doi: 10.1016/j.ijrobp.2020.12.052. Epub 2021 Jan 6. PMID: 33421557. Tamplin MR, Wang JK, Binkley EM, Garvin MK, Hyer DE, Buatti JM, Boldt HC, Grumbach IM, Kardon RH. Radiation effects on retinal layers revealed by OCT, OCT-A, and perimetry as a function of dose and time from treatment. Sci Rep. 2024 Feb 9;14(1):3380. doi: 10.1038/s41598-024-53830-6. PMID: 38336828; PMCID: PMC10858219. Keywords: radiotherapy, proton, optic toxicity