Gamma Knife (GK) Radiosurgery for Pituitary Adenomas: Evaluation of a Series of 163 Patients

Abstract

We have analyzed a group of 163 patients with pituitary adenoma treated by the GK for 5 years. They were followed up for 12–60 months (median 24 months) after irradiation. An antiproliferative effect has been achieved using the minimal dose 16–35 Gy with median of 20 Gy to the tumor margin in all of our patients who were controlled by MRI (n = 126 patients). One-half of these adenomas noticeably decreased in size. This antiproliferative dose was safe for the surrounding structures. The effect was not dependent on the gender or age of the patient, on previous fractionated radiotherapy, or on the applied dose. A significant dependence was found on the invasive growth of adenoma, on the use of a modern planning system (GammaPlan) in relation to the older Kula system, and on previous microsurgery. The hormonal normalization has been achieved in 50.4% from 133 hypersecreting adenomas (39/91 = 43% of acromegalics, 11/13 = 85% of patients with Cushing's disease, 2/9 = 22% of patients with Nelson's syndrome, 11/18 = 61% of prolactinomas). The median latency of the effect was 12 months. The minimal dose to the margin of hypersecreting adenomas was 10--45 Gy, median 35 Gy. The hormonal normalization was not dependent on the gender, on previous surgical resection, fractionated radiotherapy, or on the volume of adenoma. The dependence of the treatment result could be proved in relation to the age, the invasive growth of the tumor, the level of its hypersecretion, the size of adenoma, the radiation dose to the tumor, and the use of a modern planning system (GammaPlan). Rare side effects were provoked only by increasing the dose to influence the hypersecretion. This led to partial or complete hypopituitarism in 3.7% of patients and left one patient with homonymous hemianopia (0.6%). A longer follow-up should disclose the possible late effects of radiation and its potency of preventing adenoma recurrences. Radiosurgery by GK has the same value for pituitary adenomas as other treatment procedures: microsurgery, pharmacotherapy and fractionated radiotherapy--therefore, it can contribute to optimizing the treatment results by combining several of the available treatment methods.