The Leksell Coordinate Frame G is utilized for functional neurosurgery, stereotactic biopsies and Gamma Knife radiosurgery. Frame placement is a critical step in these procedures and can represent a challenge for proper alignment especially for smaller programs that may have limited staffing support to assist in placement. Multiple techniques are used to provide stability for frame application including ear bars, over-the-head Velcro or mounted bar, air cuffs and base frames for supine placement.1-3 The selection of the stabilization method is often driven by physician preference and experience, patient preference, and availability of resources.
We have developed a novel stabilization system for Gamma Knife radiosurgery and allows a single operator to apply the Leksell frame in an efficient and reproducible manner. Our bite-bar stabilization system (BBSS) also adds a pin-length calibration guide to the stabilization system to allow for optimal pin length choice every time. The BBSS can be used interchangeably with the ear-bar system based on surgeon preference.
Application of the BBSS and stereotactic frame placement is performed by a single neurosurgeon prior to radiosurgery. The bite-bar holder frame device is slid onto the sides of the Elekta Leksell Coordinate Frame G base and secured lightly, near the back of the frame with two screws (Figure 1). The stereotactic frame is placed over the patient’s head and the bite-bar component is attached to the holder frame device. Once the patient bites down gently, the stereotactic frame can still be angled up or down, or the bite can be released to allow the entire frame to be adjusted forward and backward. This allows for a final adjustment to move the frame more posteriorly for occipital/cerebellar targets or more anteriorly for frontal targets. Once an optimal position has been obtained the BBSS will hold the frame securely, allowing experienced personnel to proceed with local anesthetic and pin placement in a standard fashion. This system also has pin calibration guides, which are screwed into position through the standard disposable plastic inserts (Figure 2). The calibration guides indicate the exact pin length required for each location when gently pushed to the surface of the skin. The hollow calibration guides provide additional stability and provide a conduit for accurate injection of local anesthetic. Once the local anesthetic is administered the calibration guides are removed and replaced with the appropriate pins. After pin placement, the stabilization frame is removed by removing the bite bar and loosening the two screws holding the frame in place. The bite-bar system is constructed of lightweight aluminum and can be sterilized and cleaned using standard hospital procedures. The bite-bar mouthpiece is an individual metal component that can be replaced each time to allow multiple patients to use this equipment in a short time interval (same treatment day). The bite surface is covered with soft silicone for bite comfort. Sterilization of the bite plates permits re-use between treatment days.
Figure 1.
The bite-bar stabilization system (silver) with bite plate attached to a Leksell stereotactic frame.
Figure 2.
Calibration guide for measuring exact screw lengths.
The BBSS has been utilized for 186 patients at our facility and by multiple neurosurgeons between January 1, 2018 and December 31, 2020. Advantages of this system are: (1) no support staff are required to assist in frame application, which is of particular value in peripheral radiosurgery centers without dedicated residents or operate with limited nursing staff, (2) fine adjustments in position can be locked into place before pin placement, (3) the bite-bar can be sterilized and re-used, and (4) there is no irritation of the external ear canal that can be associated with ear bars. The ear-bar or alternative frame stabilization system may be a better choice in patients with irregular or nonexistent teeth or bite. In addition, patients sensitive to sedation may not be able to maintain a sufficient bite.
The unique skull pin calibration system serves multiple purposes. When screwed into place the needle guides can be extended to not only provide an estimate of optimal skull pin length but also help stabilize the frame by placing gentle pressure at the insertion points. This eliminates the potential confusion of pin selection, additional measuring devices, and reduces the risk of needing to replace pins that are inappropriately sized after tightening. The injection of local anesthetic through the skull pin calibration system prevents unwanted movement until the actual pins can be individually placed. This helps prevent any angulation or malalignment in the frame.
Bite-bar and vacuum suction mouth pieces have been previously described for use in stereotactic radiotherapy for head-and-neck cancer with immobilization using a well-fitting mask and headrest.4-5 For single-fraction radiosurgery, the stabilization needs to be considerably more rigid and sustained and is often achieved using stereotactic frame placement. Utilization of a bite-bar for the brief period of frame placement has aided frame placement for the neurosurgeons at our institution.
In summary, bite-bar stabilization provides an adjunctive method that can be used with the existing methods of frame application used world-wide. Leksell frame application can be performed by a single operator using the BBSS allowing for reduction in support staff required to assist frame application. The addition of a skull pin calibration guide for screw length further simplifies the procedure. These benefits may be of particular value for smaller centers with less experience or fewer personnel. Further studies are needed to evaluate patient-reported outcomes and patient satisfaction with bite-bar stabilization during frame application.
Acknowledgments
The authors would like to acknowledge Johnathan Tyler, Ph.D. (Tyler Research Corp., Edmonton, Alberta, Canada) for fabricating and donating the prototype BBSS to our institution. Dr. Tyler did not have any role in the preparation of the manuscript.
Grant Support
This project was supported by an unrestricted grant, The George and Eileen Smith Fund, from the University Hospital Foundation (Edmonton, Alberta, Canada).
Authors’ disclosure of potential conflicts of interest
The authors have nothing to disclose.
Author contributions
Conception and design: Keith Aronyk
Data collection: Angela Pickering, Gregory Bowden
Data analysis and interpretation: All authors
Manuscript writing: Keith Aronyk, Gregory Bowden, Samir Patel
Final approval of manuscript: All authors
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