Evaluation of the effects of radiotherapy on macroprolactinomas using the decline rate of serum prolactin levels as a dynamic parameter.

The effect of radiotherapy (24- > 50 Gy) on serum prolactin levels was studied in 28 patients with macroprolactinomas. All had been treated with surgery and 21 had also received bromocriptine interim therapy. Serum prolactin levels decreased in a log-linear fashion with time, both in the patients who never received bromocriptine and those who were treated with this drug. The decline rate of serum prolactin, which thus represented the effect of radiotherapy, was independent of intercurrent bromocriptine therapy, radiation dose and variables such as pre-radiation prolactin levels, tumour grade and tumour extension. During the course of follow-up (3-24 years) serum prolactin normalized in eight patients (28.6%). It is proposed to use the decline rates as a dynamic parameter to predict normalization time and time required for continuance of dopaminergic drug therapy.