Neovascular glaucoma after proton beam therapy of choroidal melanoma: incidence and risk factors.

PURPOSE

To analyze the risk factors for the development of neovascular glaucoma (NVG) of patients with choroidal melanoma after proton beam therapy (PBT).

METHOD

Clinical case series, retrospective study. We evaluated 629 consecutive patients receiving proton beam therapy for the treatment of a choroidal melanoma at the oncology service at Charité, Berlin and Helmholtz-Zentrum, Berlin between 05/1998 and 11/2008 regarding the development and risk factors of NVG. Patients with tumor resection, salvage proton beam therapy for recurrent disease and known glaucoma of other origin were excluded from the cohort.

RESULTS

Of the 629 patients matching the inclusion criteria, 20.8% developed neovascularization of the iris after a mean time of 2.0 years (range 0.45 to 8.4 years) after PBT. Forty-seven percent of the patients with a neovascularization of the iris developed NVG after a mean time of 2.0 years after PBT, ranging from 5 months to 11.6 years. Univariate analysis revealed tumor height [p < 0.001, hazard ratio (HR): 2.71, 95% confidence interval (CI): 1.36-5.35 for tumors >6 mm ≤9 mm and 11.32 (4.03-31.73) for tumors >9 mm], distance of the tumor to the optic disc (p < 0.001, HR: 0.43, 95% CI: 0.24-0.77 for >0 mm ≤3 mm and HR: 0.13, 95% CI: 0.04-0.37 for >3 mm), dose to the ciliary body (p < 0.001, HR: 9.21, 95% CI: 5.08-16.71 (21-40 cobalt gray equivalents (CGE), HR 27.23, 95% CI: 6.33-116.97 (41-60 CGE)), dose to the optic disc (p < 0.001, HR: 3.53, 95% CI: 1.11-11.27 (21-40CGE), HR: 5.37, 95% CI: 2.72-10.63 (41-60CGE)), the irradiated length of the optic nerve (p < 0.001, HR: 4.48, 95% CI: 2.47-8.13) and diabetes mellitus (p < 0.05, HR: 2.53, 95% CI: 1.4-4.5) were found to be risk factors for the development of NVG. Multivariate regression analysis identified the dose to the ciliary body [p < 0.001, HR: 4.39, 95% CI: 2.28-8.44 (21-40 CGE), HR: 11.04, 95% CI: 1.97-61.69 (41-60 CGE)], the irradiated length of the optic nerve (p < 0.001, HR: 3.88, 95% CI: 2.11-7.16), the existence of diabetes mellitus (p < 0.01, HR: 1.28, 95% CI: 1.24-4.21) and tumor height [p < 0.05, HR: 2.28, 95% CI: 1.17-4.83 (>6 mm ≤9 mm), HR: 3.74, 95% CI: 1.05-13.23, (>9 mm)] to be independent risk factors for the development of NVG.

CONCLUSIONS

In the present analysis we found tumor height, dose to the ciliary body, irradiated length of the optic nerve and diabetes mellitus to be risk factors for the development of NVG. Whenever possible, critical structures of the anterior and posterior segment should be spared by beam shaping or changing of the beam entry angle.