Radiation therapy of ocular melanoma: pre-clinical experience

Several methods have been developed to treat ocular melanomas and trials are ongoing to obtain reliable data to ascertain the superiority of one treatment over the other in terms of local control, overall survival and frequency of side effects. In spite of the fact that enucleation is accepted to treat the larger tumours the use of radioactive plaques or proton beam irradiation are used in specialised centres and a large experience has been gained with their use. Proton beams are employed in different centres scattered all over the world and have demonstrated their superiority with respect to conventional photon or plaque irradiation. Protons have, in fact, a minimal scattering, a well defined range in tissues and may be collimated in small fields delivering most of their energy at the end of the pre-defined track. Pre-clinical experience is reviewed with particular attention to the determination of the RBE (Relative Biological Effectiveness) of the protons in comparison to 2 MV photons and to the clinical and histological modifications produced by a collimated modulated and unmodulated beam of protons. Collimated proton beams produce circumscribed areas of chorioretinal scarring without any other long-term serious complications that are usually associated with other radiation therapy modalities. In particular the well demarcated area of chorioretinal scarring present a border (0.5-1.0 mm) with transient modifications immediately surrounded by normal retina. No optic nerve damage is noticed and no serious complication is detected in the anterior segment of the eye.