Optic and peri-optic enhancement as an imaging finding after particle therapy

Background Particle therapy involving the optic nerve may cause optic neuropathy. Knowledge of post-treatment imaging findings is important for early detection. Purpose To investigate optic nerve and peri-optic enhancement following particle therapy for periorbital malignancies. Materials and methods This retrospective study included 16 patients with contrast-enhanced MRI after particle therapy (15 proton beam therapy and one heavy-ion radiotherapy), comprising 24 evaluated optic nerve sides. Two experienced neuroradiologists independently reviewed the reference and most recent follow-up MR images, and disagreements were resolved by consensus. Exploratory dose associations were evaluated using side-level logistic generalized estimating equations accounting for within-patient correlation. Results Grade 2 enhancement was observed in 7 of 16 patients (43.8%) and 9 of 24 sides (37.5%), involving the optic nerve in 6 sides and the peri-optic region in 7. Among 21 sides in 14 proton-treated patients, optic nerve enhancement was not significantly associated with maximum dose (OR per 10 Gy [RBE], 1.481; 95% CI, 0.883–2.482; p = 0.137) but was nominally associated with BED 3 (OR, 1.705; 95% CI, 1.201–2.421; p = 0.003). Peri-optic enhancement was not significantly associated with maximum dose (OR, 1.479; 95% CI, 0.734–2.980; p = 0.274) or BED 3 (OR, 1.490; 95% CI, 0.999–2.222; p = 0.051). One patient was clinically diagnosed with RION; no visual symptoms were documented in the remaining 15 patients. Conclusion Optic nerve or peri-optic enhancement may occur after particle therapy, including in patients without documented visual symptoms, and may represent subclinical radiation-related injury or nonspecific post-radiation changes.