Daily patient setup error in prostate image guided radiation therapy with fiducial-based kilovoltage onboard imaging and conebeam computed tomography.

Background: This study examined the interfraction setup error in patients undergoing prostate radiotherapy using fiducial markers and on-board imaging.

Methods: Patients (n=53) were aligned to the treatment isocenter by laser followed by orthogonal kilovoltage (kV) radiographs to visualize bony anatomy and implanted fiducial markers. The magnitude and direction of couch shifts for isocenter correction required was determined by image registration for bony anatomy and fiducial markers.