Simulation of Medical Linear Accelerators with PENELOPE

Abstract

Monte Carlo simulation of clinical linear accelerators (linac) allows accurate estimation of the absorbed dose in a patient. However, its routine use in radiotherapy units has been hindered by the difficulties related to efficient programming of the simulation files and the usually long computation times required. penelope is a Monte Carlo general-purpose radiation transport code that describes the coupled transport of photons, electrons and positrons in arbitrary materials and complex geometries. Although penelope by itself is perfectly suited for the simulation of linacs, it nevertheless imposes a programming effort on the end users wishing to do so. In this chapter a brief review is given on several programs that facilitate the simulation of linacs and computerised tomographies using penelope as the Monte Carlo engine. Variance-reduction techniques implemented in these codes, which allow an efficient simulation of linacs, including multileaf collimators, are also described. The chapter ends with an example of a simulation with penelope of a linac irradiating a highly conformed small electron field used for the treatment of the conjunctival lymphoma of the eye. The example shows the simulation of a linac and a computerised tomography of a segmented eye.