Role of biological effective dose for prediction of endocrine remission in acromegaly patients treated with stereotactic radiosurgery

Purpose Stereotactic radiosurgery (SRS) can be used in acromegaly patients to achieve endocrine remission. In this study we evaluate the biological effective dose (BED) as a predictor of SRS outcomes for acromegaly. Method This retrospective, single-center study included patients treated with single-fraction SRS with growth hormone secreting pituitary adenomas and available endocrine follow-up. Kaplan-Meier analysis was used to study endocrine remission, new pituitary deficit, and tumor control. Cox analyses were performed using two models [margin dose (model 2) versus BED (model 1)]. Results Sixty-seven patients (53.7% male) with a median age of 46.8 years (IQR 21.2) were treated using a median dose of 25 Gy (IQR 5), and a median BED of 171.9Gy(2.47) (IQR 66.0). Five (7.5%) were treated without stopping antisecretory medication. The cumulative probability of maintained endocrine remission off suppressive medications was 62.5% [47.9-73.0] at 3 years and 76.5% [61.0-85.9] at 5 years. IGF1(i) > 1.5 was a predictor of treatment failure [Hazard ratio (HR) 0.40 (0.21-0.79) in model 1, p = 0.00783]. Margin dose > 22 Gy [HR 2.33 (1.06-5.13), p = 0.03593] or a BED > 170Gy2.47 [HR 2.02 (1.06-3.86), p = 0.03370] were associated with endocrine remission. The cumulative probability of new hypopituitarism after SRS was 36.8% (CI 95% 22.4-45.9) at 3 years and 53.2% (CI 95% 35.6-66) at 5 years. BED or margin dose were not associated with new hypopituitarism. Conclusion BED is a strong predictor of endocrine remission in patients treated with SRS. Dose planning and optimization of the BED to > 170Gy(2.47) give a greater probability of endocrine remission in acromegalic patients.