The primary concern when performing Gamma Knife surgery for pituitary adenoma is preservation of vision and pituitary function while achieving tumor growth control. Higher prescribed radiation doses are typically correlated with higher incidences of postradiosurgical hormone deficiencies. The goal of the present study was to retrospectively analyze the feasibility of using a lower prescribed radiation dose in the treatment of nonfunctioning pituitary adenomas and the effect of this dose on vision, pituitary function, and tumor growth control.
The study was conducted in 38 patients with nonfunctioning pituitary adenomas, who were treated between January 2002 and July 2008. Twenty-one patients were available for follow-up (13 men and 8 women). The mean follow-up period was 44 months (range 24–90 months). Nineteen patients had previously undergone surgery. Pituitary dysfunction developed after surgery in 3 patients. One patient had an abnormal pituitary hormone profile before radiosurgery due to an attack of pituitary apoplexy. Visual field defects were present in 12 patients. The prescribed radiation dose was 12 Gy in all patients. The tumor volume ranged from 0.5 to 11.8 cm3 (mean 4.8 cm3). The maximum dose to the visual pathway was kept below 10 Gy. The mean maximum dose delivered to the visual pathway was 7.9 Gy.
The patients were followed up for a period of 24 to 90 months (mean 44 months). The size of the tumor decreased in 11 patients (52%) and remained stable in 9 patients (43%). In 1 patient there was tumor growth outside the previous radiation field (on the contralateral side). Among the 12 patients with visual field defects, 9 (75%) experienced an improvement and the remaining patients' vision remained stable. In only 4 patients was the visual improvement associated with tumor shrinkage. The hormone profile remained normal in all patients except for the 4 patients who had pituitary dysfunction before radiosurgery.
The 12-Gy prescribed dose used in this study seems to be sufficient for producing tumor control while sparing the patient from radiation-induced pituitary dysfunction. In addition, visual improvement was reported in a number of cases. A larger series and longer follow-up are required to confirm these results.