Characteristics of electron beams from a medical microtron

The Instrument AB Scanditronix MM22 medical microtron provides ten electron beam energies from approximately 3 to 22 MeV. Isodose curves, depth dose curves, field uniformity, and other characteristics were measured in water and in polystyrene. The method of acceleration, dual scattering foil system, and collimation technique produce beams having features superior to many other medical electron accelerators. Maximum dose rates at isocenter varied from about 500 to over 900 cGy min-1, photon contamination from 0.6% to 4.1%, and surface doses from 70% to 95% of the maximum. Depth dose curves were indistinguishable from those with identical practical ranges of a scanned beam linac at energies less than 18 MeV, and field flatness was clearly superior to the scanned beam linac at standard treatment distances.