SU-E-J-137: Hybrid EOE and EOI Dynamic Gating for Effective Image Guided Radiation Treatment

Abstract

Purpose: Respiratory gating can potentially reduce normal tissue complications and increase tumor local control, however, with prolonged treatment delivery time. To enhance the efficiency of beam delivery, dynamic hybrid gating approaches have been proposed. Methods: Three approaches have been proposed and they are differ when to update the gating window. (1) to update the gating window whenever a peak EOI (end-of-inhale) is not in the current gating window; (2)to update the gating window whenever a new peak EOI is identified, where weighting factors will be used to determine gating window position. The variations of the sliding windows of previously acquired data used in gating window determination have also been investigated. Evaluation metrics, including duty cycle, beam delivery time, beam toggling rate, and their changes have been quantified and compared along with static EOE (end-of-exhale) gating and static hybrid EOE-and-EOI gating. Results: Simulated over motion data of 400 treatment fractions from 15 patients have been performed. For static gating, gating window sizes of 2, 3, 4, and 5 mm have been performed. Duty cycles of both EOE and EOI gating increase with the gating window sizes, with EOE gating triples EOI gating. The beam toggling rate of EOI gating is lower than that of EOE gating. With hybrid dynamic gating, the mean beam delivery time was decreased by more than 25% from static EOE gating to static hybrid gating and over 5% from static hybrid gating to dynamic hybrid gating. The average beam toggling rate increased within 20% from static EOE gating to static hybrid gating and decreased over 5% from static hybrid to dynamic hybrid gating. Comparison of the three dynamic hybrid gating approaches showed that there was no significant difference among them. Conclusion: The dynamic hybrid gating will improve the accuracy of gated radiation treatment and reduce gated treatment time.