Dose perturbations at interfaces in photon beams: annihilation radiation.
A model is presented for estimating the contribution of annihilation radiation to the dose perturbation at interfaces between high and low atomic number materials. The contribution is small, but not negligible relative to the total interface dose perturbation. The maximum contribution occurs for photon beams of about 8 MeV in energy. For an 8-MeV beam passing first through lead, then through polystyrene, the annihilation radiation contribution to the interface dose perturbation is about 8%, at a copper/polystyrene interface, the contribution is about 7%, and at an aluminum/polystyrene interface, the contribution is about 3%.
Department of Therapeutic Radiology, University of Minnesota Hospital and Clinic, Minneapolis 55455.
B L
BL
Werner
D001842:Bone and Bones / Q000528:radiation effects; D006801:Humans; D008433:Mathematics; D008962:Models, Theoretical; D011827:Radiation; D011878:Radiotherapy / Q000379:methods