Monte Carlo Modelling of a Mini Multi-Leaf Collimator for Radiotherapy: Development of a Multi-Leaf Collimator Component Module Using a Modified EGSnrc Platform

The use of Multi-Leaf Collimators (MLC) in radiotherapy treatments allows to shape the radiation field to the target volume, exploiting the potential therapeutic gain of a better spatial localisation of the radiation beam. Therefore, it is essential to be able to fully characterise the dosimetrical properties of these devices, including the proper Monte Carlo modelling of its physical properties. This work describes the development and validation of a calculation model for a Siemens ModuLeaf mini MLC using a modified EGSnrc Monte Carlo platform. This environment was developed as a Monte Carlo working tool which enables an easier implementation of the EGSnrc code system through its simplified structure and the use of advanced programming tools, allowing a much more transparent code development. These concepts are proved through the development of a component module (CM) for the Moduleaf. The validation of this new CM allowed us to validate the Monte Carlo calculation model, demonstrating its usefulness which enhances the dosimetric characterisation of the Moduleaf with respect to experimental measurements.