Proton Therapy for 166 Patients with Iris Melanoma: Side Effects and Oncologic Outcomes

Abstract

To investigate the oncological and functional outcomes of a large cohort of patients with a favorable stage of circumscribed and diffuse iris melanoma who underwent primary proton treatment and the risk factors related to initial tumor characteristics and the treatment field architecture. Retrospective, single-center, case study. We reviewed 225 patients with iris melanoma who were consecutively treated with proton beam therapy at our institution between 1998 and 2020. We performed Kaplan-Meier time-to-event analyses and multivariate Cox proportional hazard analyses to identify the impacts of tumor characteristics and target volumes on oncological and functional outcomes. We measured local tumor control, eye preservation rates, metastasis-free survival, cataract and glaucoma-directed surgery, intraocular pressure, and changes in visual acuity. Of the 192 patients with tumors confined to the iris (T1a-c) who underwent proton therapy as primary treatment, a total of 166 patients (mean age 58.4 years; 88 females) with a minimum follow-up of 6 months were included. Multifocal or diffuse tumor spread was present in 77 (46.4%) patients. The median follow-up time was 54.0 (IQR: 27.4-91.8) months. Local recurrence occurred in 2 patients (1.2%) with circumscribed iris melanoma. Enucleation was a rare event (n=5, 3%) and no patient developed metastatic disease. A large treatment field (full aperture, involving >10 clock hours) was identified as a risk factor for the development of secondary glaucoma (HR: 6.3; p<0.001) and subsequent surgical interventions (HR: 10.85; p<0.001). The large treatment field group showed a significant decline in visual acuity (logMAR >0.3; log-rank p<0.0001), which was associated with secondary glaucoma (HR: 3.40; p=0.002). Proton therapy provides an effective, non-invasive treatment option for patients with a favorable stage of iris melanoma. Irradiation of the anterior segment up to 10 clock hours is associated with a low risk of the development of secondary glaucoma and vision loss.