Quantitative Analysis of Respiratory Gating Accuracy based on RPM Synchronized Pre- and Post-Treatment Fluoroscopy on Abdominal Patients

Abstract

Results: A decrease in gating accuracy was observed in 44% of movie pairs, with 17 out of 40 movie pairs in Fractionated-pancreas patients and 7 out of 15 movie pairs in SBRT-Liver patients. Three main causes for decreased gating accuracy were identified as non-optimized gating window (52%), change of EIC over time (42%) and patient motion (6%). The extra 2 mm margin between set-up and treatment aperturewas able to compensate for most of gating uncertainty for both SBRTand fractionated patients. Whena 5mm f-ptvwas modeled, gatingaccuracyimproved from 77%±14%to 95%±5% for all 24 post-treatment movies with decreased accuracy, except for one SBRT movie whose accuracy still below 50%. Conclusions: Quantitative analysis of respiratory gating accuracy indicated that i) inconsistent correlation between external and internalmotionisinherentforfreebreathingpatients,butdoesnotnecessarilyrelatetodecreaseofgatingaccuracy;andii)thereis a limitation in choosing gating window manually based on real-time fluoroscopic movies. In order to improve/maintain gating accuracy during treatment, we suggest using at least a 2mm or greater difference between the f-PTVand CTV-PTVexpansion to account for residual error. Author Disclosure: J. Ge: None. L. Santanam: None. P.J. Parikh: B. Research Grant; Varian Medical Systems.