Gamma knife radiosurgery for acromegaly--long-term experience.

OBJECTIVE: The Leksell gamma knife (LGK) is one of the treatment options for pituitary adenomas. We report on our long-term experience treating acromegaly using LGK.
DESIGN: Since 1993 we have followed 96 acromegaly patients through periods of from 12 to 120 months. The mean follow-up period was 53.7 +/- 26.8 months. Seventy-two patients were treated with neurosurgery prior to LGK; for 24 LGK was the primary treatment. Thirteen patients were irradiated twice, due to persistent activity of the adenoma or its residue. Pituitary functions were tested at 6-month intervals, post-irradiation. The target tumour volume for radiosurgery was between 93.3 and 12 700 mm3 (median 1350 mm3).
RESULTS: Fifty per cent of the patients achieved mean GH < 2.5 microg/l within 42 months, normalized their IGF-I within 54 months, and achieved GH suppression in the oral glucose tolerance test (oGTT) < 1 microg/l with normal IGF-I within 66 months. LGK effectiveness was dependent on initial adenoma hormonal activity (GH and IGF-I serum levels), not on the size of the adenoma. Patients with primary neurosurgery followed by LGK irradiation had better outcomes than those with LGK alone. Irradiation arrested all adenoma growth, causing tumour shrinkage in 62.3% of patients. Twenty-six developed hypopituitarism when irradiated by 15 Gy (or more) on functional peritumoral pituitary tissue. No hypopituitarism appeared using lower doses.
CONCLUSIONS: In acromegaly, LGK is a useful adjunct to primary neurosurgery when treating post-surgical residues because it can limit the duration of medical therapy. It can be used as a primary therapy when neurosurgery is not possible.