Room: Exhibit Hall | Forum 6
Purpose: To investigate the feasibility of real-time tracking lung tumor motion using continuous 2D ultrasound (US) and periodic 2D x-ray images created from cone beam projection images (CBPI).
Methods: Time-sequenced b-mode US and CBPI data were extracted from the data acquired with the ClarityÂ® and XVI platforms on an Elekta linac. The data was synchronized through a video capture card (VCE-PRO, IMPERX Inc.) which was triggered by the XVI system. In this way, a system was configured to allow real-time acquisition of the diaphragm position synchronized with periodic acquisition of the lung tumor position. Feasibility of the system was demonstrated by acquiring synchronized data from ultrasound images of diaphragm and CBPI of lung tumor on three lung cancer patients consented to participate in the study. The data were acquired in two fractions for each patient.
Results: The intrafractional CBPI acquired during VMAT delivery was successfully synchronized with US acquisition. The US system was able to track the motion phantom with an accuracy of within 2 mm. The optimized position for the US probe was found to be between the volunteerâ€™ ribs near the diaphragm to reduce attenuation of ribs to US signal, and minimized potential organ deformation. Ease of diaphragm visualization was decreased with the body size of the volunteer. Significant correlations were observed between diaphragm motions measured from US and CBPI (R2= 0.99, p Ë‚ 0.0001), also between the motions of the diaphragm measured by US and the lung tumor measured by CBPI for all patients (R2= 0.97, p Ë‚ 0.0001).
Conclusion: It is feasible to monitor lung tumor motion in real time during RT delivery by using continuous US to track diaphragm motion and 2D periodic x-ray images to verify tumor position.
Funding Support, Disclosures, and Conflict of Interest: This work was partially supported by Elekta
Image-guided Therapy, Organ Motion, Radiation Therapy