Robustness of X2 Anchor Point Tracking to Breathing Pattern Changes during Biology-Guided Radiotherapy
Abstract
Purpose
To evaluate the robustness of the developmental X2 Anchor Point Tracking algorithm to changes in breathing patterns between SCINTIX-modeling PET (for planning) and biology-guided radiation therapy (BgRT) treatment.
Methods
Four experiments were conducted in which breathing patterns were different between BgRT planning and delivery. A 22-mm ball target was filled with 18F-Fluorodeoxyglucose (FDG), and it was placed inside an FDG-filled cylinder fitted inside an ArcCHECK and placed on a CIRS motion platform moving with various cos4 waveforms. The tumor-to-background ratio was 10:1 and an EBT-XD film was placed inside the coronal plane of the target. Plan 1 simulated for 4s period and 10mm peak-to-peak amplitude, while amplitude increased to 15 mm during delivery. Plan 2 simulated for 4s period and 15 mm amplitude but delivered to 10mm amplitude motion. Plan 3 simulated using 4s period and 15 mm amplitude but delivered to 8s period to simulate slower breathing. Plan 4 simulated using 8s period and 15 mm amplitude but delivered to 4s period to simulate faster breathing. Treatment was performed using a X2 system that tracks the ball using the Anchor Point Tracking algorithm currently in development. Dosimetric accuracy on the film was evaluated using 3%/2m absolute dose gamma and film margin loss, which is defined as the loss of coverage of the PTV by 97% isodose line.
Results
All four BgRT scenarios were successfully delivered. The gamma pass rates for plans 1, 2, 3, and 4 were 96.5%, 93.5%, 90.0%, and 95.6%, respectively. The PTV margin loss results were 2.1, 0.9, 0.8, and 0.6 mm, respectively.
Conclusion
Dosimetric accuracy was achieved by the prototype X2 system with Anchor Point Tracking even when breathing pattern changes in amplitude or period; thereby providing evidence to show that the X2 is robust to changes in patient breathing patterns.