A simple proposal to reduce cervical target movement during Leksell Perfexion Gamma Knife radiosurgery

L. Dade Lunsford, MD1, Jagdish Bhatnagar2, L. Dade Lunsford3

1Department of Neurological Surgery, University of Pittsburgh 2Pittsburgh, United States 3University of Pittsburgh

Keywords: radiosurgery, Craniovertebral junction, cervical spine, technique, gamma knife

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     The design of the Leksell Perfexion® (PFX) Gamma Knife facilitates inferior target stereotactic radiosurgery (SRS) providing that the target itself is above the standard G-frame base ring. Concern has been raised about the potential of target movement in the region from the occiput to C4. 
     This study documents the potential target deviation using the current Leksell frame.
     A commercially available skull and cervical spine model was adapted for SRS using the Leksell PFX Gamma Knife. Both CT and fluoroscopic imaging were performed to determine the potential for target deviations at standard Gamma Knife angles of 70, 90, and 110 degrees. In addition, target deviation at various heights of the patient positioning table was compared to a standard 90 degree angle.
     Multiple radio-opaque targets embedded in the model showed target deviations which ranged from as low as 0.58mm at the medial C1-occiput junction to 13.32mm at C3-4 during 70° extension. Target deviation relative to a 90° CT scan at 110° flexion showed deviations that ranged from 2.79mm at the C1-occiput junction to 17.53mm for the medial target at the C3-4 junction. Relative to a PFX shoulder table height of 4.5cm, target deviation at a height of 3cm varied from 0.436mm to 5.255mm. For a height at 5.5cm, target deviation varied from 0.436mm to 3.598mm. For a height at a maximum of 5.8cm, target deviation varied from 0.617mm to 4.298mm. Using the standard G frame, placed as inferiorly on the head as possible using ear bar extenders, we can reliably image to C4 using MRI and CT co-registration. A commercially available cervico-thoracic MRI compatible brace placed before frame application will significantly reduce target deviation related to imaging and treatment portions of SRS procedures.
     This concept remains to be validated in patients.
     As expected, target deviation grossly exceeds clinical tolerance and was determined to be greater the further the distance from the occiput to the cervical spine target. 
     Simple and reproducible methods that allow centers to treat inferior targets reliably without the need for reengineering the currently widely available G frame may increase the range of targets that can be treated effectively using the current model of the LGK PFX.


Project Roles:

L. Lunsford (), J. Bhatnagar (), L. Lunsford ()