External beam radiation therapy is concerned with the precise and accurate delivery of radiation for cancer treatment. Highly-collimated beams are generated in a linear accelerator, consisting of several hardware components that move around the patient in a complex geometry to allow radiation target the tumor from every possible angle. The complex arrangements of the hardware components may give rise to collisions among the components or between the components and the patient. We present a premiere Web-based 3D visual simulator that enables early detection of collision scenarios based on the accurate 3D representation of a specific linear accelerator model and volumetric patient-specific CAT scan data.