Optimizing the beam-shaping system in a gamma radiotherapy apparatus

We have related the design features of the head in a gamma apparatus to the beam parameters, particularly the stability of these. We examined the geometrical visibility of the three-dimensional radiation source at various points in a plane at the nominal source-surface distance (SSD) as affected by the geometrical dimensions and any possible defficiencies in the collimation system. We considered the source-shutter-diaphragm system and corrected for the self-absorption in the source. The following initial data were used in calculating the visibility: source radius, height, shutter thickness, distance from shutter to end of source, and diameter and conicity of the shutter hole. Similar dat for the diaphragm were used in calculating the effects on the beam parameters.