[The irradiation of air-filled cavities in a plexiglass phantom using 42 MiV bremsstrahlung]

For the investigation of dose distributions as they are produced by the existence of cavities within the irradiated volume, a nonhomogeneous plexiglass phantom has been exposed to a 42 MeV radiation due to retarding of particles. Depth dose curves as well as the ion dose of the interface being more distant from the focus have been measured using different dimensions and depths of the cavity. The modifications of the dose distribution are essentially due to the density difference producing the displacement of the depth dose curve and to multiple scattering effects. The displacement of the depth dose curve amounts to about two thirds of that dimension of the cavity which runs parallel to the radiation axis. An increase or a decrease of the ionization within the air-filled volume results from multiple scattering effects and in dependent on the shape of the cavity.