Conventional pituitary irradiation is effective in lowering serum growth hormone and insulin-like growth factor-I in patients with acromegaly

Background: There has been recent controversy as to the effectiveness of conventional pituitary irradiation in reducing circulating GH levels to less than 2.5 ng/ml and/or normalization of serum IGF-I. Objectives: Our objectives were to determine the effects of conventional pituitary irradiation on 1) lowering of serum GH and IGF-I levels, 2) the proportion of patients who achieve a GH level less than 2.5 ng/ml and a normal age-corrected IGF-I and the time taken to achieve this, and 3) the incidence of hypopituitarism and other adverse effects. Design: We conducted retrospective data collection from 14 centers throughout the United Kingdom. Patients: We studied 1840 patients with acromegaly, of whom 884 had received conventional pituitary irradiation. Measurements: We assessed circulating GH and IGF-I levels and pituitary function at intervals after irradiation. Results: Mean GH levels declined from 13.5 to 5.3 ng/ml at 2 yr after irradiation, to 2.0 ng/ml by 10 yr, and to 1.1 ng/ml at 20 yr. Twenty-two percent of patients achieved a level less than 2.5 ng/ml by 2 yr, 60% by 10 yr, and 77% by 20 yr. The interval to achieve this depended on the preirradiation GH level. IGF-I levels fell in parallel to those of GH with 63% of patients having a normal level by 10 yr. The proportions of patients with new pituitary hormone deficiencies 10 yr after irradiation were 18% for LH/FSH, 15% for ACTH, and 27% for TSH. No other side effects were noted. Conclusions: In this, the largest series reported, conventional pituitary irradiation is shown to be an effective and safe means of reducing both serum GH and IGF-I concentrations in patients with acromegaly.