Frameless Stereotactic Placement of Brachytherapy Seeds within a Pituitary Adenoma via Endoscopic, Endonasal Approach: A Technical Note

Introduction: Recurrent pituitary adenomas are challenging lesions. The standard second-line treatment after surgery is radiotherapy. After radiotherapy, there is no standard third-line treatment. At our institution, we have utilized I-125 seeds as brachytherapy for treatment-refractory pituitary adenomas. The placement of the seeds requires precision to maximize target tissue exposure and minimize radiation dose to surrounding structures; therefore, the seeds must be placed under stereotactic navigation. For pituitary adenomas, stereotactic placement of seeds presents a unique challenge given the safest, and easiest exposure is in a narrow corridor via an endonasal approach. Here we present a technical note on the use of frameless stereotactic guidance for placement of brachytherapy seeds within a pituitary adenoma.

Case Description: A 67-year-old male with a nonsecreting pituitary adenoma presented with imaging progression. He had undergone three prior surgeries, two prior treatments with photon radiotherapy, and three cycles of temozolomide. The decision was made to pursue brachytherapy with I-125 seeds. A preoperative MRI with thin slices through the sella was utilized to create the target for each of the two planned seeds. The targets were chosen by the radiation oncology team. A thin slice CT head was performed on the day of surgery and merged with the planning MRI in the Brainlab (Brainlab, Munich, Germany) interface. The patient was taken to the operating room and placed under general anesthesia. He was positioned in a standard fashion for an endoscopic, endonasal approach to the sella in cranial pin fixation in the head holder. Facial registration was performed with the Brainlab soft-touch. The typical endoscopic, endonasal approach was then performed. The Varioguide Brainlab frameless stereotactic navigation device was then brought into the field. A safe trajectory was chosen to the preplanned targets. The first I-125 seed was then placed under stereotactic guidance at the first target. The second seed was then placed in similar fashion. The small defects in the dura were covered with fibrin glue. The patient was then extubated and admitted to the floor overnight. Postoperative CT confirmed appropriate placement of the seeds. The patient tolerated the procedure well and was discharged the following day.

Conclusion: Brachytherapy is a viable treatment option for treatment-refractory pituitary adenomas. Frameless stereotactic navigation provides excellent accuracy for placement of the radioactive seeds through a small aperture such as the nasal passage while obviating the technical challenges of a stereotactic frame.

No conflict of interest has been declared by the author(s).