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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.

Fifteen patients were treated in the Gamma Knife Unit and followed for 18 months or longer. Four patients had Cushing's disease, 4 had acromegaly, 3 had Nelson's syndrome and 3 had prolactinomas. One patient had no endocrinopathy. One of the patients with acromegaly and 2 of those with prolactinomas had been operated prior to Gamma Knife treatment. Radiological tumor localization was not an insuperable problem in this series. The effect of Gamma Knife treatment on the anterior pituitary neoplasia, as such, was consistently successful. All the tumors which received 10 Gy or more to the edge showed either a reduction in volume or at least cessation of growth. On the other hand, the effect of the treatment was less consistent in respect to the endocrinopathies. These results are discussed in respect of dose and tumor size. It is suggested that the role of the Gamma Knife in the treatment of pituitary adenomas requires further clarification, based on prospective studies.