Gamma-ray buildup factor and radiation absorbed dose enhancement at tissue-bone interfaces

Abstract During superficial radiotherapy, and for cases where bony structures lie relatively close to the surface behind the tissue region being treated, perturbations to delivered dose are expected due to the change in tissue scattering conditions and the value of buildup factor near the tissue/bone interface. The absorbed dose distribution within bone, muscle, and muscle-bone-muscle interfaces was estimated for photons within the energy range 0.05 to 1.333 MeV. The energy absorption buildup factor is computed using the (GP) fitting method for a geometry of adjacent layers within a multilayer tissue matrix where a thick slab of solid bone is located in-between slabs of muscles of the same thickness. It was observed that dose enhancement was limited only to a few millimeters close to the interface. Also, variations in dose at the interface were found significant only for low photon energies and relatively insignificant at photon energies higher than 0.06 MeV.