SU-E-P-15: Imaging Coordination of SBRT and SRS Implementing Cone Beam CT, On-Board X-Ray Image Conjunction with Optical Image Guidance.
PURPOSE
For Stereotactic body radiation therapy patients positioning, cone beam CT imaging has been widely used, generally with zero couch rotation. To accurately position patients beyond the couch rotation limitation, the purpose of this study is to evaluate the coordination between Stereotactic radiation surgery and SBRT patient positioning technology expanding patient positioning with various couch rotation.


METHODS
Currently in our clinic a Varian Novlis Tx was utilized for treating SBRT patients implementing CBCT. A BrainLAB X-ray ExacTrac imaging system in conjunction with optical guidance was primarily used for SRS patients. CBCT and X-ray imaging system were independently calibrated with 1.0 mm tolerance. For daily imaging QA, we set up a Penta imaging phantom with infrared markers. The imaging phantom has two image isocenters for CBCT and X-ray imaging respectively with CBCT isocenter offset from the X-ray imaging isocenter. The X-ray imaging system was implemented through BrainLAB ExacTrac system with CBCT localized position at the initial zero position for the X-ray imaging system. For the other couch positions, X-ray images were fused with patient DRRs for positioning.


RESULTS
For daily imaging QA, the longitudinal, vertical and lateral coordination between CBCT and X-ray imaging averages 0.3+/-0.5, 0.2+/- 0.5 and 0.4+/-0.5 mm. The shift from the CBCT imaging isocenter to the X-ray imaging isocenter is 0.5+/-0.5 mm accuracy for a 24-month period of tracking. Patient position accuracy: After initially localizing the patient with CBCT at the zero couch position, we then position the patient with the X-ray imaging system. The computed translational and rotational shift accuracy are 0.5+/-0.6 mm and 0.5+/-0.3 degree respectively.


CONCLUSION
Accurate coordination of CBCT and X-ray imaging in conjunction with optical imaging guidance has been routinely utilized to our patient positioning with couch rotation. The X-ray imaging capability at rotated-couch positions improved the physician confidence level during SBRT treatment.