Recommissioning of the Sheffield Gamma Knife Unit following a source change

Reinstallation of the Sheffield Gamma Knife Unit was completed in early November, 1991, following the replacement of the cobalt sources. Two methods were used to evaluate the isodose configuration within the replenished unit. The first method used a scanning microdensitometer to interrogate films exposed within a spherical phantom, whilst the second relied upon a series of measurements obtained with an array of diodes. The results produced by the latter method compared more favorably with the computer-generated theoretical curves. The two sets of results are presented and some possible explanations for the discrepancies are proposed.