A CAD Interface for GEANT4

Typically used as a tool for Monte Carlo simulation of high energy physics experiments, GEANT4 is increasingly being employed for the simulation of complex radiotherapy treatments. Often the specification of components within a clinical linear accelerator treatment head is provided in a CAD file format. Direct import of these CAD files into GEANT4 may not be possible, and complex components such as individual leaves within a multi-leaf collimator may be difficult to define via other means. Solutions that allow for users to work around the limited support in the GEANT4 toolkit for loading predefined CAD geometries has been presented by others, however these solutions require intermediate file format conversion using commercial software. Here within we describe a technique that allows for CAD models to be directly loaded as geometry without the need for commercial software and intermediate file format conversion. Robustness of the interface was tested using a set of CAD models of various complexity; for the models used in testing, no import errors were reported and all geometry was found to be navigable by GEANT4.