title: Photon dose perturbations due to small inhomogeneities.
abstract: An apparatus capable of measuring small fractional changes in ionization current has been used to study the effect of small inhomogeneities on photon dose in water. Small ring-shaped inhomogeneities were introduced into a water phantom and measurements have been made for 4-, 6-, and 18-MV x-rays. The results show beyond the range of secondary electrons, the dose perturbation is basically a photon transport phenomenon which becomes less important as the beam energy increases; within the range of secondary electrons, dose perturbation also involves electron transport, which has a strong dependence on atomic number and could result in a substantially large effect on dose deposition.
mesh_terms: D055592:Biophysical Phenomena; D001703:Biophysics; D004579:Electron Transport; D006801:Humans; D008953:Models, Anatomic; D011879:Radiotherapy Dosage; D011882:Radiotherapy, High-Energy; D012542:Scattering, Radiation