The Effect of External Pituitary Irradiation on Elevated Serum Prolactin Levels in Patients with Pituitary Macroadenomas

The response of serum prolactin to external radiotherapy was studied in 58 patients (32 women) with pituitary tumours, aged between 16 and 75 years. Forty-four patients underwent pituitary surgery before radiotherapy. Six Patients were irradiated with a regimen of 20 Gy in eight fractions over 10–11 days and the remainder received 35–42.5 Gy in 15 fractions over 20–22 days. Following radiotherapy, 44 patients received additional treatment with dopaminergic agonists. Prolactin levels ranged from 1078 to 491000 mU/I (median 11750 mU/I) before radiotherapy and all but three patients showed a fall in serum prolactin (measured 4 weeks after stopping bromocriptine in those on dopamine agonist therapy) during observation over periods of up to 154 months. All patients had evidence of pituitary fossa erosion or expansion at presentation and large tumours (Hardy-Vezina Grade 3–4) were more common in male patients (χ2=10.08, p 4600 mU/I intially and were reduced by radiotherapy at a rate indistinguishable from that of patients with pituitary adenomas associated with disconnection hyperprolactinaemia. None achieved permanent reduction of serum prolactin to <500 mU/I. External radiotherapy is effective in reducing serum prolactin levels in patients with pituitary macroadenomas, particularly where the hyperprolactinaemia is due to true tumour hypersecretion, but normal levels may take over 10 years to achieve. Radiation-induced hypothalamic damage probably contributes to the hyperprolactinaemia persisting after therapy and together with tumour-associated or radiation-induced hypopituitarism accounts for the poor prospects for fertility in female patients.