Treatment of macular degeneration with proton beams

Subfoveal neovascular membranes (SNVMs) are a leading cause of severe visua l loss in the elderly in the United States. Previously, the only treatment that could halt progression of this disease was laser photocoagulation, whi ch was, however, accompanied by immediate reduction in visual acuity. A sin gle narrow proton beam was used to irradiate 45 patients to either 8 or 14 Cobalt Gray Equivalent. The alignment technique and dosimetry of these trea tments are described. The proton beam direction, range, and modulation were planned with the assistance of an eye-specific planning program. A single anterior beam was used, with patients looking nasally toward a blinking fix ation Light at an angle of 30 degrees. Patients were aligned using a light field projected through a slit collimator. Patients' positions were monitor ed during treatment with a short-focal-length camera. Depth dose in a flat phantom was measured with a small-diameter parallel plate ionization chambe r. Lateral profiles were measured at several depths with silver halide film . Each treatment session lasted 15 min, of which 1 min consisted of beam de livery. The proton beam stopped in the orbital cavity, delivering no primar y proton dose to the brain. Dose to the center of the lens of the involved eye was less than 0.5% of the dose delivered to the macula. Treatments of S NVMs with proton beams require only a short visit to the hospital, little i mmobilization effort, and a minimal amount of treatment room and beam time. Compared to previous treatment trials using x-ray beams, the dose to nonoc ular tissues is reduced significantly. (C) 1999 American Association of Phy sicists in Medicine. [S0094-2405(99)02605-X].