3155 - Single-Fraction Image-Guided Stereotactic Radiosurgery for Ocular Melanoma: Dosimetric Analysis of Optic Pathway Constraints

Purpose/Objective(s): Eye preservation of uveal melanoma usually is done with brachytherapy, or proton therapy. Access to these treatments is limited in low- to middle-income countries. Stereotactic radiosurgery, with Gamma Knife or linear accelerator is an emerging treatment modality in this setting. We report our early experience, and the dosimetric evaluation of single-fraction stereotactic radiosurgery (SRS), with SRS modern image guidance, and a six-degree-of-freedom couch (Elekta Versa HD Linac, Elekta AB, Stockholm, Sweden). We propose that SRS can achieve adequate target coverage, while maintaining acceptable doses to critical visual structures, with tumor proximity to the optic pathway representing the main planning constraint.

Materials/Methods: We retrospectively reviewed consecutive patients (n=12) with uveal melanoma treated with single-fraction SRS (2022–2026). Extracted variables included demographics, tumor subsite, dimensions, GTV/PTV volumes, and distance from tumor to the ipsilateral optic nerve (DTN). Treatments involved fiducial-based targeting, image guidance, and retrobulbar anesthesia for ocular immobilization. Statistical analysis included Spearman’s correlation to assess the relationship between DTN and optic nerve Dmax, and a Mann-Whitney U test to compare juxtapapillary (<5mm) vs. non-juxtapapillary lesions (p < 0.05).

Results: Median patient age was 54 years (range 27–75). Most received 35 Gy in 1 fraction (10/12). Median GTV 0.4 cc and PTV 0.7 cc. Median DTN 8 mm (range 0–21), and median optic nerve Dmax 11 Gy (range 7.5–43.5). A moderate-strong negative correlation was observed between DTN and optic nerve Dmax (rho = -0.56) was observed. Juxtapapillary lesions received significantly higher doses compared to non-juxtapapillary tumors (median Dmax 14.0 Gy vs 9.8 Gy; p= 0.033). Median lens Dmax 29 Gy (range 2.7–44.1). SRS planning was achievable in all patients, with dosimetric trade-offs primarily driven by tumor proximity to visual structures.

Conclusion:

In this early experience, single-fraction uveal melanoma SRS using contemporary image guidance demonstrated favorable dosimetric feasibility across a heterogeneous cohort. Tumor proximity to the optic pathway emerged as the dominant determinant of planning trade-offs. These findings support SRS as a potential eye-preserving treatment option in settings where conventional ocular radiotherapy modalities are not readily accessible and highlight the importance of standardized reporting of optic nerve distance and visual-organ dose metrics for cross-series comparison.