Room: Exhibit Hall | Forum 8
Purpose: To quantify the accuracy of a real-time template matching algorithm (Varian Medical Systems) use to track a vertebral body during arc dose delivery
Methods: Using a DICOM spine plan based on a CT study of a torso phantom with 1 mm slice spacing, and a contoured vertebral body target, templates were generated of the target projection for every 1 degree of gantry rotation. Prior to all measurements of tracking accuracy, the imaging geometry re-calibration of the radiotherapy treatment machine was performed. The phantom was positioned using a CBCT scan and corrected using a 6 degree of freedom couch. The dose was delivered with the kV imaging system deployed. High quality kV images acquired at 2 Hz during a VMAT SBRT dose delivery were used to track the vertebra target. Accuracy of the tracking algorithm was assessed as the displacement of the target from zero on two different Linacs, TB1 and TB2. Accuracy of template matching with MV images with a 10cm x 10 cm open field 180 degree arc plan was also investigated.
Results: Registrations were performed in 888 kV images. The maximum errors in the lat/vert and longitudinal directions were 0.3 and 0.5 mm. The corresponding average errors were 0.1 and 0.21 mm. No significant differences were found between the two machines, or between the kV panel positioned at 50 cm or 80 cm. The average MV 2D error vector length was 0.22 mm. Template matching failed on 2 of 110 MV images
Conclusion: Results indicate that real-time template matching is sufficiently accurate to provide clinics with a means to greatly improve the safety and clinical robustness of high dose spinal SBRT treatments.