Three-dimensional dose calculations for radiation treatment planning. Photon Treatment Planning Collaborative Working Group.

We discuss geometric and physical aspects of dose calculational methodologies as developed and implemented in three-dimensional treatment planning systems at four institutions participating in an NCI Contract for the Evaluation of High Energy Photon External Beam Treatment Planning. The geometric aspects include such issues as unconventional beam orientations, 3-D patient geometry, image data requirements, and pathlength calculation in 3-D. The physical aspects deal primarily with the formalisms employed in dose calculations. Exact calculation of dose is impractical due to the complex manner in which radiation interacts with matter. Approximations have to be made which limit the accuracy of dose calculations. For a number of situations of clinical interest, especially for regions where electronic equilibrium does not exist, the accuracy of conventional methods of dose calculations is suspect. New, more accurate methods have been proposed but have not been implemented to date. Three-dimensional dose calculations are very time consuming with currently available general purpose computers. With the development of the next generation of computers and other ancillary hardware and with continuously evolving algorithms, accurate and fast three-dimensional dose calculations should become affordable for the radiotherapy community in the near future.