| A three dimensional dose calculation method for gamma rays in heterogeneous media has been developed. Dose at a point is computed by performing a volume integration of contributions from all volume elements in the irradiated medium. The dose contribution from each volume element is determined by following the transport and deposition of energy by photons and electrons resulting from first photon collisions. A unique feature of this method is that it takes into account the transport of electrons as well as the multiple scattering of photons. This method has been applied to dose calculations for monoenergetic and polyenergetic photons in a homogeneous medium. As a preliminary test, the calculated results were compared with the results obtained from measurements and/or from Monte Carlo calculations, and the agreement is excellent. This method was then applied to a set of special test problems of inhomogeneous finite medium, and the calculated results were again compared with the measured data and/or the Monte Carlo results. The agreement is also very good except in local, extreme cases, which are unlikely to be encountered in clinical situations. |
