Proton beam radiotherapy for choroidal and ciliary body melanoma in the UK—national audit of referral patterns of 1084 cases

Introduction Proton beam therapy has been utilised for the treatment of uveal melanoma in the UK for over 30 years, undertaken under a single centre. In the UK, all ocular tumours are treated at one of four centres. We aimed to understand the variation in referral patterns to the UK proton service, capturing all uveal melanoma patients treated with this modality. Methods Retrospective analysis of data regarding all patients treated at the Clatterbridge Proton service between January 2004 and December 2014. Results A total of 1084 patients with uveal melanoma were treated. The mean age was 57 years (range 9–90 years), basal diameter of 11.5 mm (range 2.0–23.4 mm) and tumour thickness of 3.9 mm (range 0.1–15.4 mm). The majority were TNM stage I (39%) or II (36%). The distance to the optic nerve varied from 0 to 24.5 mm with 148 (14%) of patients having ciliary body involvement. There were variations in the phenotypic characteristic of the tumours treated with protons from different centres, with London referring predominantly small tumours at the posterior pole, Glasgow referring large tumours often at the ciliary body and Liverpool sending a mix of these groups. Discussion In the UK, common indications for the use of proton treatment in uveal melanoma include small tumours in the posterior pole poorly accessible for plaque treatment (adjacent to the disc), tumours at the posterior pole affecting the fovea and large anterior tumours traditionally too large for brachytherapy. This is the first UK-wide audit enabling the capture of all patients treated at the single proton centre.