Outcome of radiotherapy for acromegaly using normalization of insulin-like growth factor I to define cure

Radiation therapy (RT) has traditionally been considered a useful additional therapy for patients with acromegaly not achieving biochemical remission after surgery. However, recent evidence has suggested that RT is not curative in most patients with acromegaly when normalization of the serum insulin-like growth factor I (IGF-I) level is used to define remission. Therefore, we evaluated the success of RT based on IGF-I level in the 47 patients who received RT as part of their treatment from the cohort of 161 patients with acromegaly seen by us between 1981 and 1999. Four patients in whom no post-RT IGF-I level was available were excluded from the analysis. Of the remaining 43 patients, 32 patients received external beam RT, 6 received fractionated stereotactic radiosurgery, 4 received γ-knife RT, and 1 received proton beam RT. The most recent IGF-I levels in these 43 patients, obtained a mean of 5.2 yr post-RT (range, 0.8-13.2 yr), were compared to age-adjusted normal ranges. IGF-I levels were normal in 17 patients (39.5%) without the addition of medical therapy. The percentage of patients with a normal IGF-I level generally increased with time post-RT; 27% of patients less than 6 yr post-RT, but 69.2% of patients 6 yr or more post-RT had normal IGF-I levels. Using the more traditional criterion for cure, a random GH measurement, 74% of patients had a GH level below 5 ng/mL, and 44% had a GH level below 2.5 ng/mL and would have been considered in remission based on these criteria. We conclude that with time RT remains a useful adjunctive treatment for many patients with acromegaly. RT should be considered along with appropriate medical therapy in selected patients who do not achieve normalization of IGF-I level after surgery or for those resistant to medical therapy.