A simple technique for treating age-related macular degeneration with external beam radiotherapy

Purpose: To develop a simple external beam photon radiotherapy technique to treat age-related macular degeneration without the need for simulation, pl anning computed tomography (CT) or computer dosimetry, Methods and Materials: The goal was to enable the treatment to be set up re liably on the treatment machine on Day 1 with the patient supine in a head cast without any prior planning, Using measurements of ocular globe topogra phy from Karlsson et al. (Int J Radiat Oncol Biol Phys 1996; 33: 705-712), we chose a point 1.5 cm behind the anterior surface of the upper eyelid (AS UE) as the isocentre of a half-beam, blocked, 5.0 x 3.0-cm, angled lateral field to treat the involved eye. This would position the isocentre about 0. 5 cm behind the posterior surface of the lens, and a little over 1 cm in fr ont of the macula, according to Karlsson et al. The setup requires initial adjustment of the gantry from horizontal (to account for any asymmetry of p osition of the eyes), then angling 15 degrees posteriorly to avoid the cont ralateral eye. Finally, the couch is raised to position the isocentre 1.5 c m behind the ASUE. Results: To verify the applicability of the technique, we performed GT and computer dosimetry on the first 11 eyes so treated. Our CT measurements wer e in good agreement with Karlsson et al. The lens dose was < 5% and the mac ula was within the 95% isodose curve in each case (6-MV linac), Treatment s etup time is approximately 10 min each day. The 11 patients were treated wi th 5 x 2.00 Gy (2 patients) or 5 x 3.00 Gy (9 patients), and subjective res ponse on follow-up over 1 to 12 months (median 4 months) was comparable to previously reported results, with no significant acute side effects. Conclusion: Our technique is easy to set up and reliably treats the macula, with sparing of the lens and contralateral eye. It enables treatment to co mmence rapidly and cost-effectively without the need for simulation or CT c omputer planning, (C) 1999 Elsevier Science Inc.