Effect of refinement of skull surface measurement on Gamma knife radiosurgery

Objective: The calculation of radiation dose and estimation of a skull collision in Gamma Knife radiosurgery (GKRS) are based on measurement of the surface of skull by a skull scaling instrument. This study was conducted to evaluate the measurement discrepancy between the Gamma Knife (GK) skull scaling instrument and actual surface as determined by MRI.Methods: 168 consecutive GKRS patients were included. Discrepancies between those values computed using the skull scaling instrument and the actual MRI were expressed as the difference between the two divided by that measured by MRI.Results: The dosage discrepancy over the deep, middle, and top targets was 3.15±0.31%, 3.51±0.37%, and 4.49±0.41%, respectively (p<.001). Mean difference in collision measurement by the caliper and predicted by the GK workstation was 4.75±0.07mm (p<.05).Conclusion: Significant differences exist in measurements between skull scaling instrument and those based on MRI. Refinement of skull measurements would make GKRS more precise.