Dosimetric Analysis of Flat versus Unflat Beams for Frameless Image guided Trigeminal Radiosurgery

Abstract

significant outlier was identified having mean local lung HU beyond two standard deviations from the mean of all patients. Upon removal of this outlier, "mean HU difference" (r 2 Z 0.56 e first fraction, and r 2 Z 0.56 e last fraction) and "local target contrast" (r 2 Z 0.48 e first fraction, and r 2 Z 0.40 e last fraction) were correlated with mean 3D vector difference. Three of 10 patients had inter-observer variability that was considered clinically significant, defined here as having a 95% confidence width greater than 5 mm. All of these patients had higher "target excursion" and/ or "local target contrast" scores compared to the remaining patients. Conclusion: Three metrics were shown here to potentially identify patients for which large inter-observer variations would be anticipated and may be used in the future to develop thresholds for additional interventions to mitigate these registration variations.