Stereotactic Photon Beam Irradiation of Uveal Melanoma

Abstract

Stereotactic photon beam irradiation has been under clinical investigation for the treatment of uveal melanoma for over 15 years. Single-fraction stereotactic radiosurgery (SRS) is usually done with a gamma knife as well as more recently with a cyberknife. The therapeutic single dose has been reduced to as low as 35 Gy over the past few years without reduction in tumor control. Doses of 40 Gy delivered at the 50% isodose result in good local tumor control and acceptable toxicity. Since radiobiological studies indicate a possible advantage of hypofractionated treatment over a single very large fraction to sterilize uveal melanoma cell lines, fractionated stereotactic radiotherapy (SRT)has gained additional interest. Besides increased tumor control, toxicity should theoretically be reduced by fractionation. Linear accelerators (LINAC) have the advantage of a feasible fractionation. Most LINAC studies employ a hypofractionated scheme of 4-5 fractions and total doses between 50 and 70 Gy. The efficacy of SRT for uveal melanoma has been proven in different studies with local tumor control rates reported over 90%, 5 and 10 years after treatment. Radiogenic side effects after SRT are reported similarly to other forms of radiotherapy, with cataract development, radiation retinopathy, opticopathy and neovascular glaucoma being responsible for the majority of secondary vision losses and secondary enucleations. Overall, stereotactic photon beam radiotherapies (SRS and SRT) are considered effective treatment modalities for uveal melanoma, with promising late tumor control and toxicity rates. Additional studies and longer follow-up are indicated to finally confirm optimal treatment modalities.