Clinical implementation of the Gamma Knife Extend System: a therapist's perspective.

Amanda Schoenberger1, Robert Dryzmala2, Joseph R. Simpson3, Eric A. Filiput4, Christine Bossung5, Karen Watts5, Bridget Burke5, Barb Kienstra5, John Reed5

1Saint Louis City, United States 2Washington University Medical School 3Washington University in St. Louis 4Barnes-Jewish Hospital / Washington University 5Barnes-Jewish Hospital

Keywords: gamma knife, Robotic, Fractionated radiosurgery, Head & Neck, fraction

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     The Extend System, a non-invasive stereotactic Gamma Knife Perfexion accessory, permits fractionated and sub-cranial treatments. The technique is useful when treating larger targets in previously treated regions or those close to adjacent risk zones. 
     We report on our initial experience with ten patients throughout bite-block fabrication, imaging, planning and treatment. We consider the impact of body habitus and location of the target on patient selection.
     Our initial experience with this technology has taught us valuable lessons for using the Extend System. We have developed procedural tips to aide in its success. Appropriate fabrication of positioning aids and a comfortable patient are keys to reproducible patient set-up and treatment. Bite-block fabrication includes a dental impression that is formed to the patient''s mouth. A plug is appropriately depressed into the impression material establishing the necessary opening for firm suction to the hard pallet. A vacuum pillow molds to the posterior head and neck. A mark placed at the top of the mold helps to insert the patient''s head properly for each treatment. A measurement from the arch of the bite-block assembly to the patent''s anterior neck or chest records the height for future setting of the treatment couch and CT couch during stereotactic imaging. Suction is then applied requiring proper technique in order to maintain the suction level necessary for patient immobilization. Once the required suction level is reached, the repositioning tool is used to record depth measurements on four sides of the skull for the CT simulation process. These values provide guidance for duplication of set-up for each subsequent treatment.
     Similar to treatment planning for the G-frame, a team of certified Gamma Knife users are required. The site, dose distribution and fractionation pattern are established by this team. Those patients appropriate for the Extend System are usually given treatments of 3 to 5 fractions over the course of 2 weeks.
     The main limitation of this study is that our experience was not quantified.
     This innovative technology has proven successful for multiple patients at our institution in the hypofractionated treatment of gliobastoma multiforme, meningioma, leiomyosarcoma, skull base metastases, and brain stem lesions.
     Learned experience is valuable to refine methods of use and clinical indications.


Project Roles:

A. Schoenberger (), R. Dryzmala (), J. Simpson (), E. Filiput (), C. Bossung (), K. Watts (), B. Burke (), B. Kienstra (), J. Reed ()