Monte carlo simulation of bony heterogeneity effects on dose profile for small irradiation field in radiotherapy.

In the radiotherapy treatment planning of a lesion located in the head region with small field radiation beams, the heterogeneity corrections play an important role. In this work, we investigated the influence of a bony heterogeneity on dose profile inside a soft tissue phantom containing a bony material. PDD curves were obtained by simulation using the Monte Carlo code EGSnrc and employing Eclipse(R) treatment planning system algorithms (Batho, Modified Batho, Equivalent TAR and Anisotropic Analytic Algorithm) for a 15 MV photon beam and field sizes of 2x2 and 10x10 cm(2). The Equivalent TAR method exhibited better agreement with Monte Carlo simulations for the 2x2 cm(2) field size. The magnitude of the effect on PDD due to the bony heterogeneity for 1x1, 2x2 and 10x10 cm(2) field sizes increases to 10, 5 and 3%, respectively.