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To evaluate clinical outcomes, including local tumour control, visual acuity, adverse events and eye preservation, of uveal melanoma patients treated at proton therapy centre HollandPTC in the Netherlands.

Since December 2019, patients diagnosed with uveal melanomas at Leiden University Medical Center (LUMC) are offered proton therapy at HollandPTC if the tumour height (including sclera) is >7-8mm and/or the tumour diameter is >16mm and/or the tumour is located juxtapapillary. Patients with smaller tumours are offered Ruthenium-106 brachytherapy. Enucleation is an alternative for those not willing or able to undergo radiotherapy. For this cohort study, we included all consecutive patients referred from LUMC for proton therapy treated up to January 31^st 2021. All patients were treated with 60.0 GyE in 4 fractions using Eclipse Ocular Proton Planning system (Varian Medical Systems, Inc.). Before treatment, tantalum localisation clips were placed on the sclera. Toxicities after proton therapy were classified according to CTCAE v4.0. Time-to-event analyses and actuarial survival rates were determined using Kaplan Meier method.

A total of 28 patients were included for analysis with a mean age of 61 years. The median initial tumour diameter and thickness were 15.2 mm (range: 7.0-20.5) and 8.3 mm (range 2.5-14.8). 39% of the tumours were located centrally, 43% mid-peripherally and 18% peripherally. At baseline 50% of the patients had a visual acuity <0.5 and 25% <0.1. The median follow-up time was 9.5 months. Tumour thickness regressed slowly after treatment and is presented in Figure 1. At one year after treatment, local tumour control, metastasis-free survival and overall survival were respectively 100%, 96% and 89%; the eye preservation rate was 96%. At one year, visual acuity was <0.5 in 89% and <0.1 in 62%. Ocular toxicities were common during the first year. The majority of toxicities were grade 1-2, but some invasive procedures had to be performed for mature cataract, vitreous haemorrhage and retinal detachments (Table 1).

Proton therapy is now available for uveal melanoma patients in the Netherlands at HollandPTC as alternative for enucleation or referral for proton therapy in Switzerland. As such, the patient selection has changed and now includes more patients with central tumours and low initial visual acuity. This is reflected in the visual outcomes and risk of toxicity. Nonetheless, local tumour control and survival outcomes were excellent.