Long-term Results of Carbon Ion Radiation Therapy for Locally Advanced or Unfavorably Located Choroidal Melanoma: Usefulness of CT-based 2-Port Orthogonal Therapy for Reducing the Incidence of Neovascular Glaucoma

Abstract

To determine the long-term results of carbon ion radiation therapy (C-ion RT) in patients with choroidal melanoma, and to assess the usefulness of CT-based 2-port irradiation in reducing the risk of neovascular glaucoma (NVG). Between January 2001 and February 2012, a total of 116 patients with locally advanced or unfavorably located choroidal melanoma received CT-based C-ion RT. Of these patients, 114 were followed up for more than 6 months and their data analyzed. The numbers of T3 and T2 patients (International Union Against Cancer [UICC], 5th edition) were 106 and 8, respectively. The total dose of C-ion RT varied from 60 to 85 GyE, with each dose given in 5 fractions. Since October 2005, 2-port therapy (51 patients) has been used in an attempt to reduce the risk of NVG. A dose-volume histogram analysis was also performed in 106 patients. The median follow-up was 4.6 years (range, 0.5-10.6 years). The 5-year overall survival, cause-specific survival, local control, distant metastasis-free survival, and eye retention rates were 80.4% (95% confidence interval 89.0%-71.8%), 82.2% (90.6%-73.8%), 92.8% (98.5%-87.1%), 72.1% (81.9%-62.3%), and 92.8% (98.1%-87.5%), respectively. The overall 5-year NVG incidence rate was 35.9% (25.9%-45.9%) and that of 1-port group and 2-port group were 41.6% (29.3%-54.0%) and 13.9% (3.2%-24.6%) with statistically significant difference (P<.001). The dose-volume histogram analysis showed that the average irradiated volume of the iris-ciliary body was significantly lower in the non-NVG group than in the NVG group at all dose levels, and significantly lower in the 2-port group than in the 1-port group at high dose levels. The long-term results of C-ion RT for choroidal melanoma are satisfactory. CT-based 2-port C-ion RT can be used to reduce the high-dose irradiated volume of the iris-ciliary body and the resulting risk of NVG.