PURPOSE: This study aimed to evaluate the long-term results of carbon ion radiation therapy (CIRT) for choroidal malignant melanoma (CMM), especially regarding the preservation of the eye and visual acuity (VA). METHODS AND MATERIALS: A total of 250 patients with intraocularly localized CMM treated with CIRT between January 2003 and September 2021 were included. The dose prescription included 60 to 85 Gy/4 to 5 fr, with only 68 Gy/4 fr used from 2018 onward. The rotating gantry system with scanning beams was introduced in April 2018. Adverse events (AEs) were graded according to the Common Terminology Criteria for AEs (version 5.0.). For secondary glaucoma, tumor-related visual field defects were excluded from the evaluation. For VA, 245 patients with VA ≥ light perception (LP) were followed up. Effective VA (≥20/200, Snellen equivalent), counting fingers, and LP were used as indicators. RESULTS: The median age was 55 (15-86) years. The T categories 1, 2, 3, and 4 were observed in 16 (6.4%), 41 (16.4%), 189 (75.6%), and 4 (1.6%) patients, respectively. With a median follow-up of 72.5 months, the 5- and 8-year overall survival rates were 87.5% and 84.2%, respectively
the 5- and 8-year local control rates were 94.4% and 92.9%, respectively. At the last follow-up, 19 of 250 patients (7.6%) underwent enucleation, 15 caused by local recurrence and 4 caused by AEs. Secondary glaucoma grades 1, 2, and 3 to 4 were observed in 22 (8.8%), 49 (19.6%), and 5 (2.0%) of patients, respectively. At the last follow-up, ≥ effective VA, ≥ counting fingers, and ≥ LP were maintained in 80 (33%), 120 (49%), and 154 (63%) of patients, respectively. Preservation rate of ≥ LP vision at 5 and 8 years after CIRT was 65.7% and 55.3%, respectively. CONCLUSIONS: CIRT for CMM is a promising treatment for both tumor control and preservation of the eye and VA.