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Barbra Hamill, Katherine A Muldrew, Michael J Quinn, Jason S Slakter, Denis O'Shaughnessy, Alan Czeszynski, Usha Chakravarthy; Microvascular changes following low dose focal radiotherapy for neovascular age-related macular degeneration. Invest. Ophthalmol. Vis. Sci. 2014;55(13):3893.
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To describe changes in the retinal microvasculature in patients with neovascular age-related macular degeneration treated with focal low dose radiotherapy (RT) using the iRAY device.
230 participants in the INTREPID clinical trial were randomised to either combination radiotherapy (16 or 24Gy) using the iRAY device with anti VEGF drug as needed versus anti VEGF monotherapy as needed. At the month 24 visit colour images and fluorescein angiograms (FA) were retrospectively examined for microvascular abnormalities (MVA) in the retinal circulation.
23 instances of MVA were called by the independent reading centre. Of these, 6 occurred in eyes that were not exposed to RT. Of the 150 participants who received RT, 17 had features of MVA. On colour images these were intraretinal haemorrhage (10); cotton wool spots (6); and microaneurysms (2). On FA, in order of frequency these were peri-vascular capillary dropout (14); staining of the wall of the microvasculature (14); irregularities of the vascular lumen (13); fluorescein leakage (13); telangiectatic vessels (8); microaneurysms (7) and bullous expansion of the microvessel tips (5). The site of the MVA was almost always located adjacent to an arteriovenous crossing; and/or in the inferonasal macula; and in half of cases was outside the nominal RT treatment zone. When MVA occurred in the arterial side of the circulation these were capillary closure and narrowing of arterioles. On the venous side these were telangiectasia, bullous tips and staining of the vessel wall. The mean area occupied by MVA in RT exposed eyes was 4.11 mm2. Follow up to M 36 was available on 3 participants in 2 of whom resolution of MVA was seen. In the 6 eyes where MVA were reported in the 80 participants not exposed to RT, these occurred in association with a retinal angiomatous proliferation (n =4) or an epiretinal membrane (n =1) and one FA was ungradable . The mean area occupied by these vessel abnormalities was 0.49 mm2.
Exposure to focal low dose ionizing radiation results in the development of characteristic MVA which are unlike abnormalities that are seen in the retinal microvasculature in the presence of chronic nAMD. RT induced MVA occurred in some 12% of RT exposed participants and showed signs of resolution in the longer term.
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