Long-term Result of Carbon-ion Radiation Therapy for Locally Advanced or Unfavorably Located Choroidal Melanoma: CT Based 2-port Orthogonal Therapy Can Reduce the Incidence of Neovascular Glaucoma

Abstract

To evaluate long-term result of carbon ion radiation therapy (C-ion RT) for the patients with choroidal melanoma and to determine the prognostic factors and risk factors of neovascular glaucoma (NVG). Between January 2001 and February 2012, 116 patients with locally advanced or unfavorably located choroidal melanoma received the C-ion RT with CT based treatment planning. Of the 116 patients, 114 patients followed longer than 6 months were analyzed for this study. Of those, 106 patients had T3 tumor and 8 patients had T2 tumor according to UICC 5th edition. Initially the treatment was performed according to a phase I/II dose-escalation protocol, therefore 16 patients treated with 60 GyE, 78 with 70 GyE, 13 with 77 GyE, and 7 with 85 GyE, in 5 fractions. Since October 2005, two-port orthogonal therapy has been started in attempting to reduce the risk of NVG, and 51 patients were already performed. Dose-volume histogram analysis was additionally performed in 106 patients with regard to NVG occurrence. Median follow up duration was 4.6 years (range, 0.5-10.6). Five-year overall survival (OS), cause-specific survival (CSS), local control rate, distant metastasis free survival rate (DMFSR), and eye retention rate of entire group were 80.4%, 82.2%, 92.8%, 72.1%, and 92.8%, respectively. NVG was occurred in 36 patients, and enucleation was undergone in 3 patients because of severe glaucoma. Three-year and 5-year NVG incidence rate was 29.7% and 35.9% for all the analyzed patients. Concerning number of port, NVG incidence rate of two-port group was significantly lower than that of one-port group on univariate analysis (p < 0.001 log-rank test): 3-year NVG incidence rate was 41.6% and 13.9% for one-port group and two-port group. Multivariate analysis identified tumor size, distance from optic disc (0-3mm vs others), and one-port therapy were independent significant risk factors of NVG; distance from optic disc (0 vs others) was independent significant prognostic factor of OS, CSS, and DMFSR. Dose-volume histogram analysis showed the average irradiated volumes of iris ciliary body were significantly lower in non-NVG group at all dose levels than NVG group. Long-term result of C-ion RT for choroidal melanoma at our institute was satisfactory, even with tumors of unfavorable size or site. This study suggests tumor size, distance from optic disc, and number of port are related to NVG occurrence; distance from optic disc is related to survival and distant metastasis. CT based two-port C-ion RT can be useful to reduce irradiated volumes of iris ciliary body and resulting risk of NVG.