Radiation therapy for subfoveal choroidal neovascular membranes in age-related macular degeneration. A pilot study

The natural course of the visual acuity of age-related subfoveal choroidal neovascularisation (CNV) membranes is poor. Laser photocoagulation of subfoveal CNV is recommended if the patient is willing to accept a large decrease in visual acuity immediately after treatment. A large proportion of patients with subfoveal CNV do not meet the Macular Photocoagulation Study Group (MPS) guidelines for laser photocoagulation. The fact that so few patients meet these criteria makes further research into new treatment techniques warranted. Ionising radiation may prevent the proliferation of endothelial cells of newly formed subretinal capillaries and may induce obliteration of the aberrant new vessels.

In this study, the effect of radiation therapy on subfoveal CNV membranes was evaluated. Four groups of ten patients were treated with external beam radiotherapy (16-MV photons) on an area of 1 cm2 (macular region) using a lens-sparing technique and total doses of 8-24 Gy. The first group received 8 Gy in one fraction. The second, third and fourth groups received 12 Gy in 2 fractions, 18 Gy in three fractions and 24 Gy in four fractions respectively. The studied parameters included best-corrected visual acuity and membrane size and leakage on the fluorescein angiogram. We included 17 occult and 23 classic CNV membranes as defined by the MPS, with a duration of less than 5 weeks at presentation. Complete ophthalmic examination including fluorescein angiography was performed before and 3, 12 and 18 months after radiation treatment. We analysed the angiogram using a standard overprojection sheet. The results concerning the visual acuity and fluorescein angiography (FA) were compared with the extensively published, natural course data.

The first group (including three cases of occult CNV) received 8 Gy in a single fraction. In this group only four of ten patients had stable visual acuity and stable FA appearance after 21 months follow-up. The visual acuity and FA remained stable after 13.6 months follow-up in seven of the patients in group 2 (12 Gy in two fractions, four occult CNV). The third group (18 Gy in three fractions, seven occult CNV) contained six patients with stable visual acuity, although two of them had CNV deterioration on the FA (11.1 months follow-up). In the last group (24 Gy in four fractions, three occult CNV), with a short follow-up of 5.6 months, eight patients had stable visual acuity and FA appearance. We did not note any regression of the CNV membrane on the angiogram. The visual acuity in groups 2, 3 and 4 decreased to 0.1 or worse in only three cases, three cases and one case respectively after at least 6 months follow-up.

Comparison of these findings with the natural history data of subfoveal age-related CNV suggests a beneficial effect of radiation therapy with a total dose of 12 Gy or more on the progression of CNV. To date no negative side effects have been observed.