Small electron beams in radiation therapy

The use of lead cutouts to produce small beams in electron therapy results in a reduced dose to the patient. The authors investigated this effect for beams with energies less than 8 MeV and diameters of 3 cm or less. Dose measurements were obtained using film and an ionization chamber. Based on these values, corrections were established to account for dose reduction due to cutout spaces and air spaces between the end of the electron cone and the skin surface. Data were also obtained on the dose increase due to backscattering from internal eyeshields.