Side Effects of Proton Beam Radiotherapy Treatment on Iris Melanoma

Abstract

This study evaluated the functional outcome and ocular side effects of patients receiving proton beam radiotherapy (PBR) for the treatment of iris melanoma (IM). This retrospective study analyzed prospectively collected data. Patients with IM who underwent PBR as a primary treatment. Treatment was given in the form of whole PBR (wPBR: n= 51) or segmental PBR (sPBR: n= 98). Visual acuity (VA) and side effects were divided into ocular surface disease (OSD), secondary glaucoma, or cataract development. A total of 149 eyes of 149 patients with a mean age of 53.9 ± 16.0 years were included. Tumor recurrence developed in 3 patients (wPBR: 1/51; sPBR: 2/98). Ocular surface disease was observed in 78.4% of the wPBR group (40/51) and 25.5% of the sPBR group (25/98) (P < 0.001) after 0.7 ± 1.2 years and 1.1 ± 0.9 years, respectively. The main side effect was dry eye syndrome in both groups, but severe side effects such as limbal stem cell failure were found only in the wPBR group (4/51; 7.8%). Secondary glaucoma developed in 31.4% of the wPBR group (16/51) compared with 1.0% in the sPBR group (1/98; P < 0.001). Glaucoma control was generally achieved with eye drops, whereas surgery was necessary in 5 patients (wPBR: 4/51, 7.8%; sPBR: 1/98, 1%). Cataract surgery was performed in 47.9% of the wPBR group (23/48) and 19.8% of the sPBR group (19/96) (P < 0.001). Before treatment, VA was 0.14 ± 0.27 logarithm of the minimum angle of resolution (logMAR) in the wPBR group and 0.04 ± 0.19 logMAR in the sPBR group. A worsening was seen in the wPBR group (0.55 ± 0.16 logMAR; P < 0.001) 6 months after radiotherapy, which normalized after 12 months (0.15 ± 0.30 logMAR; P= 0.17). In the sPBR group, no such decrease in VA was observed (6 months: 0.03 ± 0.22 logMAR, P= 0.54; 12 months: 0.04 ± 0.21 logMAR, P= 0.98). Our results demonstrate that PBR is a very successful treatment option for patients with IM, showing a high tumor control rate and relatively low complication profile. Tumor recurrence was a rare event, and secondary enucleation was not necessary in any patient. Side effects are commonly seen, but severe side effects such as limbal stem cell failure or secondary glaucoma mainly developed after wPBR. These results are important for clinical decision making and discussion with the patient regarding this form of radiotherapy. The author(s) have no proprietary or commercial interest in any materials discussed in this article.