Gamma Knife surgery for recurrent or persistent Cushing disease: long-term results and evaluation of biological effective dose in a series of 26 patients.

Here we report long-term results after stereotactic radiosurgery (SRS) with Gamma Knife (GKRS) for Cushing disease. We further evaluated the potential role of the biological effective dose (BED) in the cure of this disease. A retrospective review of a prospectively collected database (n = 26) was undertaken at Lille University Hospital, France. The mean follow-up period was 66 months (median 80, range 19–108). The mean marginal prescribed dose was 28.5 Gy (median 27.5, range 24–35) and the mean BED was 208.5 Gy2.47 (median 228.1, range 160–248). We divided patients with endocrine remission into a high BED group (160–228 Gy2.47, n = 6) and a low BED group (228–248 Gy2.47, n = 12). Eighteen (69.2%) patients had endocrine remission in the absence of any pharmacological therapy after a mean of 36 months (median 24, range 6–98). The actuarial probability of endocrine remission was 59% at 3 years and 77.6% at 7 years, which remained stable up to 10 years. There was a tendency to a higher overall probability of biological remission associated with higher BED values (77% versus 66% at last follow-up), although this did not reach statistical significance. Of note, the numbers of patients reflecting this actuarial probability at 12, 24, 36, 51 and 96 months were 21, 15, 11, 7 and 3, respectively. Tumour control was achieved in all cases (mean decrease in size for patients experiencing one was 29.4%, range 0–100%). Seven patients developed new pituitary insufficiency after GKRS. Gamma Knife radiosurgery offers high rates of tumour control and endocrine remission on a long-term basis for ACTH-secreting pituitary adenomas. In this small series, higher BED values appeared to be associated with better endocrine remission rates. Owing to the limited sample size, such results should be validated in a larger cohort.