Efficacy and safety of higher dose stereotactic radiosurgery for functional pituitary adenomas: A preliminary report

Keywords: pituitary adenoma, gamma knife, dose escalation, radiosurgery, hormone dysfunction

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     Single fraction stereotactic radiosurgery (SRS) is a common adjuvant therapy for hormonally active pituitary adenomas when surgical resection fails to control tumor growth or normalize hypersecretory activity. Marginal doses of 20-24 Gy have been used with good result although highly variable rates of endocrine remission ranging from 17-83% and median time to remission of 25-50 months have been reported. 
     We evaluated outcome data for a cohort of patients treated at our single institution with a higher dose (35 Gy) SRS for secretory pituitary adenomas.
     54 patients with secretory pituitary adenomas were referred for SRS between January 1, 1998 and December 31, 2009. We studied 33 patients  (GH: n = 16, ACTH: n = 14, Prolactin: n = 2, TSH: n = 1) who had >12 months follow up and had previously undergone trans-sphenoidal resection. Of the 21 patients excluded from this study, 11 had follow-up durations of less than 12 months, 5 were unable to receive 35 Gy due to the proximity of their tumor to the optic apparatus, and 5 had not undergone prior surgical resection. All patients were evaluated post-SRS for time to normalization of hormonal secretion, time to relapse and incidence and time course of radiation-induced hypopituitarism and cranial neuropathies.
     IRB approval was obtained for a retrospective medical record review.
     Normalization of hypersecretion was achieved in 70% of patients treated with 35 Gy to the tumor margin, with a median time to remission of 15 months. Endocrine deficiency within any hormonal axis was observed in 27% of patients. After initial hormonal remission, 17% of patients experienced endocrine relapse, with a median time to relapse of 42 months. One case of partial third nerve paresis and two cases of new onset visual defects, one of which was transient, were observed. Three patients reported frontal headaches and/or facial pain.
     This was a retrospective study.
     Time to endocrine remission was shorter in our patients treated with 35 Gy to the tumor margin than those previously reported in the literature using marginal doses of 20-24 Gy. 
     Rates of endocrine remission, post-SRS hypopituitarism and cranial neuropathies are not increased compared with lower dose treatments.


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