How effective is external pituitary irradiation for growth hormone-secreting pituitary tumors?

Forty-six patients with GH-secreting pituitary tumours were treated with conventional external pituitary irradiation through two opposed fields to a total dose of 3750 cGy over 15 fractions. Thirty-patients received external radiotherapy as primary treatment and 16 received radiotherapy combined with pituitary surgery. The mean (+/- SD) serum GH in the former group was 74.3 +/- 74.8 mU/l before treatment, falling by 28% per year over 0-5 years and by 16% per year over 0-20 years. The mean (+/- SD) serum GH in the latter group was 265.4 +/- 209.3 mU/l before treatment, falling by 76% in the first year--a direct result of surgical removal of tumour--then by 30% per year over 1-5 years and 16% per year over 1-20 years. Progressive failure of normal anterior pituitary function developed by 10 years, with variable loss of gonadotrophin, corticotrophin and thyrotrophin function. The respective figures for patients treated with radiotherapy alone were 47.4, 29.6 and 16.0% and for the combined group were 70.2, 53.9 and 38.1%. Whilst external pituitary irradiation appears to reduce serum GH concentrations in patients with GH-secreting pituitary tumours the major disadvantages of this form of treatment are the time taken to achieve a cure and the high incidence of hypopituitarism. Nevertheless there did not appear to be any other serious side effects.