Risk factors for neovascular glaucoma after carbon ion radiotherapy of choroidal melanoma using dose-volume histogram analysis

PURPOSE: To determine the risk factors for neovascular glaucoma (NVG) after carbon ion radiotherapy (C-ion RT) of choroidal melanoma. METHODS AND MATERIALS: A total of 55 patients with choroidal melanoma were treated between 2001 and 2005 with C-ion RT based on computed tomography treatment planning. All patients had a tumor of large size or one located close to the optic disk. Univariate and multivariate analyses were performed to identify the risk factors of NVG for the following parameters; gender, age, dose-volumes of the iris-ciliary body and the wall of eyeball, and irradiation of the optic disk (ODI). RESULTS: Neovascular glaucoma occurred in 23 patients and the 3-year cumulative NVG rate was 42.6 +/- 6.8% (standard error), but enucleation from NVG was performed in only three eyes. Multivariate analysis revealed that the significant risk factors for NVG were V50IC (volume irradiated > or =50 GyE to iris-ciliary body) (p = 0.002) and ODI (p = 0.036). The 3-year NVG rate for patients with V50IC > or =0.127 mL and those with V50IC <0.127 mL were 71.4 +/- 8.5% and 11.5 +/- 6.3%, respectively. The corresponding rate for the patients with and without ODI were 62.9 +/- 10.4% and 28.4 +/- 8.0%, respectively. CONCLUSION: Dose-volume histogram analysis with computed tomography indicated that V50IC and ODI were independent risk factors for NVG. An irradiation system that can reduce the dose to both the anterior segment and the optic disk might be worth adopting to investigate whether or not incidence of NVG can be decreased with it.