Cobaltotherapy dosimetric calculations over a voxelized water phantom. Validation of different Monte Carlo models and methodologies against experimental data

The main goal of the present work is to quantify, in a homogeneous water phantom, the differences between experimentally measured dose distribution inside it, and those calculated by the simulation of different transport models using the Monte Carlo computer code MCNP. This goal has been achieved simulating the electron and photon transport in a water phantom irradiated by a Theratron 780reg (MDS Nordion) ⁶⁰Co radiotherapy unit, which has been realistically modeled, considering field sizes from 5times5 to 20times20 cm². The source description and characteristics of the incident beams have been slightly modified in order to study the result variations of these models. Different methodologies have been also carried out to speed up calculations with the aim of applying MCNP efficiently in radiotherapy treatment planning