Evaluation of the positional differences between bone matching and fiducial marker matching in target localization of the expiratory breath-hold radiation therapy for pancreatic cancer.

517Background: In radiation therapy, the accuracy of target localization is very important to increase the agreement between the planned treatment and the actual dose delivered to the patient. Therefore, image-guided techniques, such as bone matching, soft-tissue matching, fiducial marker (FM) matching and so on, are used to improve the precision and effectiveness of radiation therapy. In this study, we evaluate the positional differences of the target localization between bone matching and FM matching in the expiratory breath-hold radiation therapy (BH-RT) for pancreatic cancer. Methods: We analyzed 15 patients who underwent BH-RT for pancreatic cancer using FM matching between July 2016 and August 2017 in our institution. The FMs were implanted in the pancreatic cancer using endoscopic ultrasound. Prior to each treatment session, bone matching using orthogonal kilovolt x-ray images and FM matching using cone beam computed tomography at end-exhalation (BH-CBCT) was performed. A total of 226 matching data...