Radiation Dose to the Eyes Using a “German Helmet” Field with the 4-MV Linear Accelerator

Abstract

A "German helmet" field defined by depleted uranium or Asarcola blocks was used to reduce the dose to the lens. With the uranium blocks, the lenticular dose was reduced to about 60% of the central axis dose (CAD). The Asarcola blocks reduced the lenticular dose to about 43% of the CAD. Even further reduction (15% CAD) was achieved by tilting the gantry 5 degrees or 10 degrees.