SU-E-J-48: Real Time Image Guided Localization in SBRT Lung/Liver Patients Radiation Treatment

Stereotactic body radiation therapy (SBRT) lung/liver patientradiation treatment requires high precision of patient position and target localization. For SBRT lung/liver patients positioning, cone beam CT imaging has been widely used, generally with zero couch rotation. The purpose of this study is to implement Stereotactic radiation surgery (SRS) patient positioning technology to SBRT by expanding patient positioning with couch rotation.

A Varian® Novlis Tx for SRS treatment wasused to treat SBRT lung/liver patients implementing CBCT. BrainLAB® X-ray imaging system in conjunction with optical guidance is primarily used for SRS patients. CBCT and X-ray imaging system were independently calibrated with 1.0 mm accuracy. 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.

Based on daily imaging QA records for a period oftwo years, the longitudinal, vertical and lateral coordination between CBCT and X-ray imaging average 0.3+/-0.5, 0.2+/-0.5 and 0.5+/-0.5 mm. The shiftfrom 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, the patient was positioned with the X-ray imaging system. The computed translational and rotational shift accuracy are 0.5+/-0.5 mm and0.4+/-0.3 degree respectively, based on 66 SBRT lung/liver patients couchrotations.

Accurate coordination of CBCT and X-ray imaging in conjunction with optical imaging guidance can be expanded to patient positioning with couch rotation. The X-ray imaging capability at rotated-couch positions improved the physician confidence level during SBRT lung/liver patients treatment.