Rapid Endocrine Remission After ZAP-X Gyroscopic Radiosurgery for Cushing's Disease: A Case Report

Cushing's disease is a rare but potentially life-threatening disorder caused by excessive adrenocorticotropic hormone (ACTH) secretion from a pituitary adenoma. Although transsphenoidal surgery remains the first-line treatment, radiotherapy (RT) can provide effective local and hormonal control in patients with persistent or recurrent disease; however, endocrine remission typically occurs only after several months or even years. To our knowledge, we report the first documented case of an exceptionally rapid hormonal remission following gyroscopic stereotactic radiosurgery (SRS) using the self-shielding ZAP-X system (ZAP Surgical Inc., San Carlos, CA, USA) in a patient with recurrent Cushing's disease. The patient received a single-fraction dose of 25 Gy prescribed to the 57% isodose line. Remarkably, ACTH and cortisol levels normalized within one month after SRS, accompanied by a striking improvement in clinical symptoms and no treatment-related toxicity. This case highlights the potential of the ZAP-X gyroscopic radiosurgery platform to achieve rapid biochemical control in ACTH-secreting pituitary adenomas and suggests that the unique dose distribution characteristics of this novel technology may contribute to accelerated endocrine responses.