Electron depth dose curves in inhomogeneous medium for radiation therapy: A simulation approach

Abstract

Introduction MeV energy electron beam is used very often for skin cancers treatment. Most of the time the percentage depth dose (PDD) and depth of maximum dose deposited (Dmax) is to be calculated based on homogenous medium. But the dose distribution can be significantly altered in the presence of tissue inhomogeneity such as bone, lung, and air cavities. Purpose It is difficult to determine dose distribution within or around small inhomogeneity because of enhanced electron scattering effects, therefore, accurate knowledge of dose distribution in homogeneous and inhomogeneous medium is very important for the delivery of accurate dose and treatment. Materials and methods In present work, EGSnrc Monte Carlo code has been used for the calculation of PDD curves in homogeneous and inhomogeneous medium. The bone of varying thickness is considered in water phantom to study effect of tissue inhomogeneity. Electron beam of energies 4–20 MeV have been used for the simulation purpose. Results The PDD has been estimated for the case of homogenous medium of water and bone and also for the case of bone of different thicknesses inserted before and after the build-up region in water phantom. It has been observed that the values of R90, R50, Rp have been decreased linearly with the bone thickness for all electron energies. Also it has been found that below the depth of inhomogeneity, PDD has increased by 10% for 0.8 cm of bone at 12 MeV. Conclusion It is concluded that because of inhomogeneity, PDD beyond inhomogeneity increases and after Dmax it decreases. This data could be useful for the clinicians to define dose prescription point during electron beam therapy and can achieve the perfection of treatment.