Purpose. The ROARMD study is a prospective, randomized trial assessing the efficacy of low dose external beam irradiation in exudative age-related macular degeneration. We determined the lens dose measurements and are using Scheimpflug lens photography to assess for cataract development. Methods. Fourteen Gy are administered in 7 fractions via a custom designed cerrobend collimator attatched to a 6 MV linear accelerator. Small field, CT guided treatment planning is used to determine the beam placement for administration of the macular radiation. The lateral beam is angled to 10 to 15 degrees posterior to avoid treatment of the contralateral retina. Lens dose measurements were performed in a tissue equivalent phantom using a small volume, parallel plate ionization chamber. The machine collimator settings were 3cm width by 4cm length, but the actual size of the treatment beam limited by the added cerrobend collimator was a semicircle with radius 1.5cm. This external collimator is 9.6cm thick and shields the area adjacent to the treatment volume. The lens is protected from transmitted radiation by both the external collimator and the machine's primary collimator. Results. The approximate posterior lens dose using the described treatment technique is 0.20-0.35 Gy (1.4-2.5% of the total target dose delivered). Conclusions. Radiation induced cataract is not anticipated after treatment. Scheimpflug lens photography data will objectively determine whether this dose exceeds the threshold for cataract development.
|Original language||English (US)|
|Journal||Investigative Ophthalmology and Visual Science|
|Publication status||Published - Feb 15 1996|
ASJC Scopus subject areas
- Sensory Systems
- Cellular and Molecular Neuroscience