Macular EpiRetinal Brachytherapy Versus Lucentis® Only Treatment (MERLOT)

The eye is designed like a camera, with a lens at the front and a film at the back. Using this analogy, the retina is the film in the camera. In the center of the retina is the macula, the region that absorbs focused light from the lens and creates an image of the outside world that is then transmitted to the brain.

The commonest cause of irreversible blindness in developed nations is age related macular degeneration (AMD). There are two types, 'dry' and 'wet' AMD. Wet AMD is also called neovascular AMD: It is the most damaging type and can blind people in a matter of weeks. Neovascular AMD is due to the growth of blood vessels under the retina, similar to a wound healing process. The blood vessels grow in two patterns, classic (15%) and occult (85%); these can be visualized with fluorescein angiography, a commonly used technique that photographs the macula after a fluorescent dye is injected into the arm. In most research on AMD, vision is assessed using the Early Treatment of Diabetic Retinopathy Study (ETDRS) vision chart, with results quantified in numbers of letters read correctly, from 0 (very poor vision) to 100 (very good vision).

A new treatment has recently been licensed in the UK called ranibizumab (trade name, Lucentis). This is an antibody that reduces the effect of vascular endothelial growth factor (VEGF), a chemical that mediates new blood vessel growth. This drug is injected into the eye at regular intervals (up to 12 a year, and typically 6 a year). Patients receiving 12 ranibizumab injections per year have a greater than 90% chance of maintaining their vision over 12 months (1-2). Another drug called bevacizumab (Avastin) has been used off label (without a licence) in the UK, USA and other countries, and this also targets VEGF. In non-randomized trials it showed similar results to ranibizumab, and is currently being assessed in head-to-head trials with ranibizumab in the UK and the USA.

One of the drawbacks of ranibizumab therapy is that patients require regular injections into the eye. In the UK, the National Institute for Health and Care Excellence (NICE) recommends patient with newly diagnosed wet AMD receive three consecutive monthly injections of ranibizumab, followed by 'as required' therapy based on disease activity. They estimate that patients receive eight injections in the first year, six in the second, and ongoing treatment thereafter. Patients require monthly hospital visits for life and each injection caries a small but cumulative risk of complications such as bleeding inside the eye, infection, detachment of the retina, raised eye pressure, and systemic effects such as stroke. A treatment that produced a more durable reduction in disease activity might reduce these risks, be more cost effective for the health service, and reduce the considerable burden of treatment for patients and their carers, with the prospect of fewer hospital visits. It would also give patients an alternative choice, should they not wish to undergo such regular eye injections.

Radiation has the potential to produce a more durable therapeutic effect, by targeting the proliferating cells that cause visual damage in wet AMD. It is well known that radiation can modify the wound healing process, which is a biological process similar to neovascular AMD. Previous studies with external beam radiation have shown an effect on the progression of macular degeneration. However vision was not improved - possibly due to the type of radiation used, the accuracy of delivery, and collateral damage to neighbouring structures.

Epimacular brachytherapy delivers local, controlled radiation 1-3 mm into the macula, during an operation called a vitrectomy. The proposed device will be CE marked (Conformité Européene - approved for clinical use) and is manufactured by NeoVista Inc, who have completed preliminary trials to assess the safety and feasibility of treating naive (newly diagnosed) neovascular AMD with a single application of brachytherapy. Initial data showed that epiretinal treatment stabilised vision for most patients with neovascular AMD. Phase II trials using the device with two concomitant doses of bevacizumab showed promising results with 91% of patients maintaining vision (losing fewer than 15 ETDRS letters), with an average improvement of 8.9 ETDRS letters (3). The percentage of patients whose visual acuity improved by more than 3 lines (15 letters on the ETDRS scale) was 38%. These results are similar to the large studies of monthly ranibizumab. A mean gain of 8.9 letters is more than twice the visual gain reported in large studies (HORIZON) of 'as required' dosing, as occurs in the UK.

A large, international, randomized, multicentre study of the device, used with two concomitant injections of ranibizumab, is now underway (the CABERNET study). Recruitment is occuring in the hospital of the applicant, and two other UK sites, with more sites to follow. The CABERNET study uses the device in treatment naive disease and was favourably reviewed by the Southwest Research Ethics Committee (07/H0206/50).

Whilst the CABERNET study will provide high quality data in treatment naive disease, it is not possible to rely on this study in relation to previously treated disease. Prior therapy with ranibizumab modifies the disease process, and those that respond poorly to injections differ from the majority, suggesting differences in the underlying disease process. It is therefore necessary to study the subset of patients with refractory disease, if valid clinical conclusions are to be reached. Furthermore, because there is limited vitreoretinal surgical capacity it is logical to offer surgical intervention to patients who have not responded fully to ranibizumab, rather than aim to treat all patients presenting with wet-AMD. To this end, an uncontrolled study (MERITAGE) using the device in refractory, previously treated disease has commenced, having received a favourable opinion from the Southwest Research Ethics Committee (07/H0206/55). The present randomised controlled trial (MERLOT) follows on from the Phase II MERITAGE study. It targets previously treated disease, and patients that are receiving regular ranibizumab, to determine if the device benefits this large subset of patients.