TU‐G‐BRC‐05: Daily Respiratory Gating Window Adjustment Is Necessary for Abdominal Radiation Therapy Patients: A Retrospective Analysis with Simulation 4DCT and Daily Fluoroscopy
Purpose: To evaluate the need for adjusting the respiratory gating window on a daily basis due to variability of intrafraction motion of abdominal tumorstreated with stereotactic and conventional fractionated radiotherapy. Methods: Thirteen patients (8 with livercancer and 5 with pancreatic cancer) were implanted with visicoil fiducials and treated with amplitude based respiratory gated (RPM) radiation therapy on a Varian Trilogy linear accelerator (Varian Medical, Inc.). A total of 225 fluoroscopic movies were recorded using an Intrafraction Motion Review Software (Varian Medical, Inc.) over 106 fractions with an average length of ∼15s each. Intrafraction tumor motion was represented by the amplitude (peak‐to‐trough) of the fiducial motion trace extracted from each fluoroscopic movie. The superior‐inferior motion over the course of radiotherapy was compared to the maximum motion from 4D‐Computed Tomography (4DCT). Results: All patients showed predominant motion in superior‐inferior direction ranging from 1mm to 29 mm. The motion varied on a day to day basis, with changes of amplitude up to 6.7±5.4 mm for liver‐SBRT patients and 7.8±2.0 mm for pancreas‐fractionated patients. The maximum motion from 4DCT was compared to individual fractions for all patients. For liver‐SBRT patients, 4DCT overestimated the motion on 5/ 27 fractions (average 6.4 mm); and underestimated motion on 11/27 fractions (average 6.8 mm). For pancreas‐fractionated patients, 4DCT overestimated the motion on 60/79 fractions (average 13.6mm); and underestimated the motion on 16/79 fractions (average 7.9 mm). Conclusions: Observed intrafraction motion range varied from fraction to fraction and majority of treatment fractions (88%) were either overestimated or underestimated by 4DCT. These results suggest the need for daily respiratory gating window adjustment for a more accurate and efficient delivery.