Prism representation: a 3D ray-tracing algorithm for radiotherapy applications.

Computing the intersection of a line with a volume, or 'ray tracing' as it is commonly known, is an integral component of three-dimensional radiotherapy dose calculation algorithms. Examples of ray tracing include the intersection of a ray from the radiation source with the patient, with heterogeneous volumes within the patient and with beam-modifying devices, such as a wedge or compensator. Ray tracing is also of primary importance in the field of three-dimensional computer graphics. Through the process of ray tracing, various display features, such as hidden surfaces, shadows, reflection and refraction, can be rendered simply and with startling realism. Advances have recently been made in three-dimensional ray-tracing methods in computer graphics. Due to the similarity of ray tracing in three-dimensional computer graphics and radiotherapy, these new techniques have an immediate application to the ray-tracing problems in three-dimensional radiotherapy dose calculations. The purpose of this paper is to present these advances and illustrate their use in radiation therapy.