Gamma Knife radiosurgery for acromegaly: evaluating the role of the biological effective dose associated with endocrine remission in a series of 42 consecutive cases.

INTRODUCTION Stereotactic radiosurgery (SRS) is a valuable treatment option for persistent and/or recurrent acromegaly secondary to growth hormone (GH) secreting pituitary adenoma (PA). Here, we assess the role of biological effective dose (BED) received by PA treated with SRS in relation with endocrine remission. METHODS Forty-two patients (minimum 6 months follow-up) were included. Mean marginal dose was 27.7 (median 28, 20-35) and mean BED received by tumor was 193.1 Gy2.47 (median 199.7, 64.1-237.1). Based on the median values, we divided the patients in high tumor BED group (H-BEDtm, 199.7-237.1 Gy2.47, n=12) and low BED one (L- BEDtm, 64.1-199.7 Gy2.47 , n=10). The two groups did not differ by pretherapeutic IGF-1 levels (p=0.1) or by the prescribed dose (p=0.6). RESULTS Mean follow-up period was 62.5 months (median 60.5, 9-127). Probability of IGF-1 normalization was 65% at 3 years and 72.4% at 4 years, remaining stable until last follow-up. Twenty-two (52.4%) patients had complete endocrine remission in absence of any Somatostatin analogues. Actuarial rates were 33% at 3 years and 57.4% at 7 years, further remaining stable during follow-up course. In univariate analysis, only statistically significant parameter was pretherapeutic serum IGF-1 and IGF-1 index (p=0.01). Five patients (5/26, 19.3%) without previous hypopituitarism developed new pituitary insufficiency. H-BEDtm was associated with higher rates of endocrine remission compared with L-BEDtm, with actuarial probability of 70.2% versus 48.2% at 9 years, although this did not reach statistical significance (p>0.05). CONCLUSION Our study confirms that SRS by Gamma Knife is safe and effective for GH secreting PA. Pretherapeutic serum levels of IGF-1 were only statistically significant parameter for endocrine remission.