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.