Initial experience with the eXtend System: a relocatable frame system for multiple-session gamma knife radiosurgery

Abstract

Objective: To present our initial experience with the Elekta eXtend System, a relocatable frame system for multiple-fraction or serial multiple-session radiosurgery.

Methods: The eXtend System comprises a carbon-fiber frame system known as the eXtend Frame, a vacuum cushion, and a vacuum pump/vacuum surveillance system. The eXtend Frame comprises a carbon-fiber frame, a mouthpiece with dental impression, and a configurable front-piece that accepts the mouthpiece and rigidly attaches to the carbon-fiber frame. Treatment preparation involves creating a dental impression, fitting the patient to the frame system at the Gamma Knife, acquiring a stereotactic computed tomography (CT) scan, and co-registering a volumetric magnetic resonance image. Measurements taken at the time of CT imaging using high-precision electronic probes locate the patient's head within the eXtend frame. These measurements are compared to measurements taken at the time of treatment to ensure the patient is in proper treatment position. Vacuum surveillance interlocks pause the treatment if the patient moves within the eXtend frame.

Results: As of June 2010, we have treated four patients at the University of Virginia with the eXtend System. In all cases treated to date, we were able to complete all fractions of the prescribed treatments. In addition, while in some cases repositioning before a given fraction required several attempts, we were able to achieve a radial repositioning error of less than 1 mm without taking new reference measurements and repeating patient setup and imaging.

Conclusions: Gamma Knife radiosurgery (GKRS) has traditionally been a single-fraction treatment modality. The eXtend System expands the range of indications for GKRS to those that may benefit from multi-fraction or serial multi-session techniques. The relocatable eXtend frame can provide non-invasive head fixation while maintaining a high accuracy, high dose, and the steep gradients associated with GKRS.