Background and purpose: Proton and stereotactic radiotherapy with photons (SRT) are both used to treat choroidal melanomas in proximity to optic disk and fovea centralis, a situation where plaque therapy is prone to complications. A comparative treatment- planning study was done to assess the capability of both modalities to preserve vision.
Patients and methods: In ten patients treated with 68-MeV protons, SRT with 6-MV photons was planned. Structures most important for visual acuity (fovea and optic disk, optic nerve) were contoured identically for both therapies. Safety margins of 1.5 mm for proton therapy were reduced to 1.0 mm for SRT.
Results: Proton-beam therapy was superior in eight of ten situations, and this result did not differ significantly by changes in the weighting of the different parameters analyzed.
Conclusion: When dose deposition to those structures most important for the preservation of vision is taken into account, under the conditions examined proton therapy offers an advantage in the majority of the patients evaluated.