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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.

A study was made of the interaction between Gamma Knife shots of different diameters, located at the same target coordinates. The effect of the doses was calculated by the Kula program and confirmed by film dosimetry. It could be shown that intermediate collimator sizes can be simulated in this way, so that, for example, a 4- and 8-mm shot with the same target coordinates simulates a 6-mm collimator. A coaxial 8- and 14-mm shot simulates an 11-mm collimator and a coaxial 14- and 18-mm shot simulates a 16-mm collimator. Additional intermediate collimator sizes can be simulated by changing the weighting of the two coaxial shots. The sharpness of the dose fall of the simulated coaxial shots is of the same order as that of single shots, indicating that the technique does not depart from ordinary Gamma Knife technique in any significant way.

In Bergen, 20 patients with meningiomas have been treated with a follow-up period in excess of 1 year. While this is too short a period to allow more than tentative conclusions to be drawn, some trends can be determined nonetheless. There has been some variation in the reporting of the results of treatment of meningiomas, with one group producing a reduction in size in 7% of patients and another in 34%. In the current material, 10 patients received 10 Gy or less to the edge of the tumor. In 4 of these 12 patients there was increase in the volume of the tumor within 1 year of treatment. Ten of the patients received 12 Gy or more to the edge of the tumor. Of these 10 patients, 4 had tumors which showed a reduction in volume. It is suggested that the difference in the reported rate of tumor volume reduction is related to differences in dose, which is discussed in relation to other treatment parameters.