EGS and Medical Physics
In the early 1980s, several simultaneous events lead to development of the current version of EGS.
- The SLAC Radiation Physics Department began working with their counterpart at KEK (Hideo Hirayama) in Japan to extend the flexibility of EGS, with special focus on design of future high-energy accelerators.
- A detailed low-energy benchmarking project was underway at the National Research Council of Canada (NRCC). This project, led by Dave Rogers, involved adopting EGS for use as a theoretical tool in ionizing radiation standards to serve the low-energy radiation protection (such as for diagnostic x-ray) and radiotherapy communities.
- Scientists outside the field of high-energy physics started using the code to solve low-energy problems, such as those found when using x-rays in medical applications. However, limitations were found when applying EGS to solve low-energy problems.
- Radiotherapy treatments were changing from use of relatively low-energy Cobalt-60 gamma rays (about 1.25 MeV) to the radiation produced by higher energy electron linear accelerators (4 - 50 MeV). At these higher energy levels, electron transport complicates dose calculations, and medical physicists needed a tool to predict the correct treatment dose.
As a result of these events, a collaboration was formed between SLAC, KEK and NRCC that lead to the release of the EGS Code System Version 4 (EGS4) in 1985. This latest version of the code is a general-purpose package that uses Monte Carlo simulations to calculate the effect of coupled transport of electrons and photons in an arbitrary geometry for particles with energies above a few keV and up to several TeV - a much wider energy range than the previous version of the code.
Interest in EGS by medical physicists has been overwhelming and worldwide. Almost daily, requests for the program are received and more than 4,000 copies have been distributed to date. More than 80 percent of the requests come from scientists working in medically-related fields. Because EGS was designed to calculate electron transport effects, an experiment was designed to see if the code would, in fact, predict the dose alterations expected by discontinuities, such as those encountered in the human body. The experiment was performed using an air or aluminum cylinder in a water tank, which was then exposed to a beam from a 20 MeV accelerator. The results clearly showed that EGS predicted the dose alterations caused by discontinuities (air/water or air/aluminum interfaces) downbeam from the radiation. This experiment gave medical physicists confidence in the ability of EGS to simulate passage of electrons through the human body.
