Clinical Outcomes of Proton Beam Therapy for Choroidal Melanoma at a Single Institute in Korea

Abstract

Purpose: This study retrospectively evaluated the clinical outcomes and complications of proton beam therapy (PBT) in a single institution in Korea and quantitatively analyzed the change in tumor volume after PBT using magnetic resonance imaging (MRI).

Materials and methods: Twenty-four treatment-naïve patients who underwent PBT for choroidal melanoma between 2009 and 2015 were reviewed. Dose fractionation was 60-70 cobalt gray equivalents over 5 fractions. Orbital MRIs were taken at baseline and 3, 6, and 12 months after PBT and annually thereafter. The tumor volume was reconstructed and evaluated by stacking the tumor boundary in each thin-sliced axial T1-weighted image using MIM software.

Results: The median follow-up duration was 36.5 months (range, 9 to 82 months). One patient had suspicious local progression and two patients had distant metastasis. The 3-year local progression-free survival, distant metastasis-free survival, and overall survival rates were 95.8%, 95.8%, and 100%,respectively. Five Common Terminology Criteria for Adverse Event ver. 4.03 grade 3-4 toxicities were observed in four patients (16.7%), including one with neovascular glaucoma. The mean tumor volume at the baseline MRI was 0.565±0.084 mL (range, 0.074 to 1.610 mL), and the ratios of the mean volume at 3, 6, and 12 months to that at baseline were 81.8%, 67.3%, and 60.4%, respectively.

Conclusion: The local controlrate and complication profile after PBT in patientswith choroidal melanoma in Korea were comparable with those reported in a previous PBT series. The change in tumor volume after PBT exhibited a gradual regression pattern on MRI.

Keywords: Choroid; Melanoma; Proton therapy; Toxicity; Treatment outcome.

Fig. 1.

A case of proton beam therapy (PBT) planning in eyeball model of a patient with choroidal melanoma. (A) Fundoscopic finding suggested the tumor located near 2 disc diameter from macula. (B) Beams-eyed view. (C) Dose distribution of PBT in fundus view. (D) Dose volume histogram.

Fig. 2.

Survival curves. LPFS, local progression-free survival; DMFS, distant metastasis-free survival; OS, overall survival.

Fig. 3.

The volumetric change in the choroidal melanoma of each patient. Solid lines show the volumetric changes in recurrent tumors. (A) Absolute changes in tumor volume. Thick solid lines show the changes in the mean volume 12 months after proton beam therapy. (B) The relative changes in tumor volume. The thick solid line shows the regression of the relative volume. The thick and short-dashed lines represent the regression lines of patients with large tumors. The thick and long-dashed lines represent the regression lines of patients with small tumors.