NTRODUCTION:Here we report long-term results afterstereotactic radiosurgery (SRS) with Gamma Knife(GKRS) for Cushing disease. We further evaluated the po-tential role of the biological effective dose (BED) in thecure of this disease.METHODS:A retrospective review of a prospectively col-lected database (n = 26) was undertaken at Lille UniversityHospital, France. The mean follow-up period was 66months (median 80, range 19–108). The mean marginalprescribed dose was 28.5 Gy (median 27.5, range 24–35)and the mean BED was 208.5 Gy2.47(median 228.1, range160–248). We divided patients with endocrine remissioninto a high BED group (160–228 Gy2.47, n = 6) and a lowBED group (228–248 Gy2.47, n = 12).RESULTS:Eighteen (69.2%) patients had endocrine re-mission in the absence of any pharmacological therapy af-ter a mean of 36 months (median 24, range 6–98). Theactuarial probability of endocrine remission was 59% at 3years and 77.6% at 7 years, which remained stable up to10 years. There was a tendency to a higher overall prob-ability of biological remission associated with higher BEDvalues (77% versus 66% at last follow-up), although thisdid not reach statistical significance. Of note, the numbersof patients reflecting this actuarial probability at 12, 24, 36,51 and 96 months were 21, 15, 11, 7 and 3, respective-ly. Tumour control was achieved in all cases (mean de-crease in size for patients experiencing one was 29.4%,range 0–100%). Seven patients developed new pituitaryinsufficiency after GKRS.CONCLUSONS:Gamma Knife radiosurgery offers highrates of tumour control and endocrine remission on a long-term basis for ACTH-secreting pituitary adenomas. In thissmall series, higher BED values appeared to be associ-ated with better endocrine remission rates. Owing to thelimited sample size, such results should be validated in alarger cohort.