AMD: Radiation Treatment and Safety
Wet AMD is treated with injections of anti-VEGF agents directly into the back chamber of the eye. Anti-VEGF drugs work by targeting VEGF (Vascular Endothelial Growth Factor), a protein involved in causing new blood vessel formation. In AMD, these new blood vessels are unstable and tend to leak fluid and blood under the retina, causing loss of central vision. The anti-VEGF drugs work by reducing the activity of VEGF, thereby temporarily inhibiting the growth and permeability of new blood vessels.
Ranibizumab (Lucentis®) is an anti-VEGF agent specifically approved to treat wet AMD. According to AMD Alliance International, the recommended treatment schedule for patients with neovascular AMD is a monthly injection for three consecutive months and further injections as needed depending on the recurrence of fluid as shown by optical coherence tomography (OCT) or eye examination.
Another anti-VEGF drug, bevacizumab (Avastin®), is used off-label by many physicians to treat wet AMD. Off-label use means that the drug has not been specifically approved by the regulatory agencies for the condition it is being used to treat. Bevacizumab is an approved drug for some forms of cancer, but has not been approved for use in AMD.
An earlier drug, pegaptanib (Macugen®), was the first anti-VEGF agent to be cleared by the FDA for treatment of wet AMD. It is still in use today, but has been largely supplanted by Lucentis and Avastin.
A newly emerging drug, aflibercept (Eylea™), has been recently introduced to treat wet AMD. It is a different type of VEGF blocker than ranibizumab or bevacizumab. Although it must still be administered via injection into the eye, this drug can potentially be given less frequently.
Treatment modalities other than anti-VEGF injections, such as photodynamic therapy, laser, and surgery, are also used in select cases of wet AMD. Although these therapies pre-date anti-VEGF drugs, they have generally not proven successful in most typical wet AMD patients and are, therefore, not widely applied.
The healthy eye contains several types of cells that provide visual function. In wet AMD, there is the formation of fragile, leaky blood vessels as well as inflammation and scarring that cause loss of vision. Anti-VEGF therapy works by temporarily suppressing the growth of new, fragile blood vessels. Radiation preferentially affects quickly dividing cells and has the potential to slow down or stop this growth selectively, as well as to reduce inflammation and scarring. Because the abnormal cells are selectively destroyed rather than temporarily suppressed, radiation may produce a more long-lasting effect than anti-VEGF injections alone.
Radiation is, and always has been, all around us. We are exposed to radiation every day from both natural background (the sun, space, the earth that we walk on) and man-made sources, including medical procedures. For example, a radiation dose is received by flying in an airplane or simply sitting on a park bench.
With the Oraya Therapy, while the local dose to the macula and nearby locations within the eye will be high, the ‘effective’ radiation dose to the whole body will be low—well below levels thought to result in a significant risk. Oraya’s system continually monitors the treatment eye position with sophisticated software to assure accurate targeting and minimize risk associated with radiation exposure to such eye structures as the optic nerve and the lens. As with any medical procedure, all benefits and potential risks of treatment must be discussed with healthcare providers and considered by each patient.
Anti-VEGF agents, such as ranibizumab (Lucentis), have a rapid onset of action but a limited durability. The underlying disease process tends to continue as the medication is naturally eliminated from the eye. Radiotherapy, in contrast, produces a slightly delayed response, but has a much longer duration of action. Both therapies target the disease in different ways, but the science suggests they act in conjunction. This rationale is supported by the oncology experience, where tumors of the colon, for example, are frequently treated with anti-VEGF agents and radiotherapy.