The capability to calculate the distribution of absorbed dose produced by photon beams and electron beams to the most general characteristics is fundamental to radiotherapy. The vast improvement of the medical imaging and localization technology over the recent past has brought a challenge to physics and computer technology to extend the computerized treatment simulation (planning and optimization) capabilities. Our photon and electron beam radiation field models have been described before. One virtue of these models is that they require relatively few experimental data and thus can be implemented very easily. The implementing of our beam treatment planning program (Mac TPS) on a MacIntosh II system is continuing. The system is used parallel to the existing Vax-750 based system for "conventional" multi-slice planning. However, its capability of 3-D segmented imaging is being applied extensively now, and continually expanded, guided by new demands and suggestions from the medical staff. There is a growing interest in the community. An extensive manual with several levels of user guidance has been prepared. The general approach, in particular the pull-down menu- tool box organization proves to be very efficient as to utilization in quite different other applications. 3-dimensional dose calculation in particular is very time consuming. An exploratory project has been initiated with DCRT to explore the potential of connecting our MacIntosh II system to a massive parallel processing system to alleviate this aspect. In addition to computational challenges, the project faces problems with the real-time 2-way transmission of very large amounts of data. Adequate staffing is a major problem.