Depth dose flattening of electron beams using a wire mesh bolus.

A common problem with low-energy electron beams (< 15 MeV) is their low surface dose when the incident electrons are monodirectional. This makes it difficult to deliver a uniform dose to tumor with any precision, limiting the clinical usefulness of such beams. A practical method is presented for greatly increasing the tissue depth enclosed by the 95% isodose region, while delivering the entire dose in a single uninterrupted treatment. Beam modification is achieved by placing a wire mesh of high atomic number (Z) on the treatment surface throughout the treatment. Electron beams of energies 6, 9, and 13 MeV are modified to produce a near uniform dose from the surface to the original depth of maximum, approximately doubling the depth enclosed by the 95% isodose. These beams have a step-function-like depth dose and can be arranged to deliver a constant dose to tumor located at varying depths while simultaneously sparing deeper tissues which are also located at varying depths. A single mesh design was found to be suitable for all energies.