Dosage Errors In Gamma Knife Radiosurgery By Skull Surface Measurement

Dar-Yu Yang1, Hung-Chuan Pan, PhD2

1Chang-Bing Show Chwan Memorial Hospital 2Department of Neurosurgery, University of Virginia

Keywords: physics, gamma knife, technique, Dose, dosimetry

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     Gamma knife now is the leading instrument in treatment of brain disorder such as tumor, vascular lesion, and functional disorder. Indeed, there existed discrepancy in brain surface measurement by the skull scale instrument and the real determined by imaging.
     In this study, we study the effect of skull surface discrepancy contributing to dosage errors under the different frame position, irradiate target, and number of isocenter.
     From June 2007 to August 2009, there were 200 consecutive cases of patients undergoing gamma knife radiosurgery (Perfexion Gamma Knife) at Chang-Bing Show Chwan Memorial Hospital.
     Except to the routine MRI imaging required for gamma knife targeting, all patients received additional MRI in T1W1 with slice thickness of 3mm 1cm from the top of the skull to the C1-2 junction. The skull surface and dosage discrepancy were determined based on the difference between measurements by skull scale instrument and calculated from MRI imaging findings. The dosage discrepancy related to frame position, location of targets, and number of shots was determined. The logistic regression was used to analyze the factors contributing to this discrepancy.
     There exited skull surface measurement discrepancy by skull scale measurement from the least errors (3.72±1.47 mm) over lateral position to the biggest errors of (6.65±2.24mm) over the occipital area. The frame position either in lateral or central position did not cause any significant difference on the measurement of skull surface. There was no significant dosage errors in position of frame, targets, and numbers of shots (>2). Significant dosage errors only existed in lateral position of target with single shot of treatment and this effect was contributing to significant skull surface measurement errors over the occipital area.
     This is a retrospective study.
     Significant skull surface measurement errors existed by the skull scale measurement.
     These measurement errors did not exert significant influence on dosage errors except in very special occasion, such as single shot of treatment and extreme location of target.


Project Roles:

D. Yang (), H. Pan ()