Analysis of the photon beam treatment planning data for a scanning beam machine

The characteristics of photon beams from the Scanditronix MM50 radiation therapy machine that are necessary for treatment planning are described. The MM50 uses a scanning beam instead of a conventional flattening filter to achieve flat dose distributions. At each beam energy, a scan pattern is chosen, depending on the field size; the small scan pattern ( S ) is used for field sizes up to 10×10 cm, the medium scan pattern ( M ) is used for field sizes up to 20×20 cm, and the large scan pattern ( L ) is used for the larger field sizes. The dose distributions of the beams associated with the 10 MV S , M , and L scan patterns, the 25 MV S , M , and L patterns, and the 50 MV S and M patterns are described. The data reported includes central axis data, beam profiles, and output factors. In addition to the measured data, our dose calculation model requires a pencil beam kernel for each beam. The kernel is constructed using the average photon energy spectrum, which is generated using a Monte Carlo simulation of the MM50. The simulation, based on EGS4 , is also used to generate the radial variation of fluence and energy fluence, which is required by a new dose calculation model that does not require the measurement of beam profiles. The Monte Carlo generated data; the photon energy spectrum, the fluence, and the energy fluence are presented.