Retinblastoma: a modification in radiation therapy technique.

Patients with retinoblastoma treated with a single lateral field often suffer multiple recurrences in the anterior portion of the retina. The authors believe that these marginal recurrences are related to dose heterogeneity and that the entire retinal surface is at risk. In an attempt to treat the entire retinal surface and still protect the lens and anterior chamber, a conventional lateral field with the anterior beam edge at the equator of the globe is used with a second anterior field in which the central divergent lens block is hung in a pendulum fashion along the central axis. The shadow of the central block projects a diameter of 10 mm at the anterior corneal surface which well encompasses the lens. The fields are weighted 1:4.5 (anterior to lateral).