Four-dimensional computed tomography prediction of inter- and intrafractional upper XXXX motion during fractionated stereotactic body radiation therapy.

@entity5 @entity1 @entity1820 @entity344
PURPOSE: Respiratory-induced @entity5 motion of upper @entity1820 during radiation therapy is often assessed using a single 4-dimensional computed tomography (4D-CT) and presumed to be representative during fractionated treatment regimens. The purpose of this study was to examine the intra- and interfraction correlations of @entity5 motion between pretreatment 4D-CT and real-time fiducial-based motion tracking in @entity1 treated with fractionated stereotactic body radiation therapy (SBRT) for upper @entity344 . METHODS AND MATERIALS: Fourteen @entity1 with @entity1820 underwent fractionated SBRT using the CyberKnife radiosurgical system with Synchrony respiratory motion management. Before treatment, each @entity1 underwent a free-breathing 4D-CT scan and fiducial motion was tracked for each phase of the respiratory cycle. Real-time fiducial positions recorded during delivery of each SBRT fraction were extracted from the CyberKnife planning system. Displacements were compared between those predicted by 4D-CT and those recorded by Synchrony during treatment in the left-right (LR), anteroposterior (AP), and superoinferior (SI) directions. RESULTS: The 4D-CT scans demonstrated little correlation with real-time mean fiducial displacement as determined by Pearson correlation with coefficients of 0.45, 0.52, and 0.63 in the SI, AP, and LR directions, respectively. Cohort-averaged maximum fiducial displacements based on 4D-CT and real-time tracking were measured to be 3.86    1.40 mm versus 10.73    7.03 mm, 2.29    1.02 mm versus 4.44    3.33 mm, and 1.45    0.49 mm versus 2.67    2.49 mm in the SI, AP, and LR directions, respectively. Mean fiducial displacements were greater than that predicted by the maximum displacements on the corresponding 4D-CT scan in 39%, 22%, and 25% of SBRT fractions in the SI, AP, and LR directions, respectively. CONCLUSIONS: Comparison of 4D-CT with real-time fiducial tracking demonstrated significant inter- and intrafractional discrepancies, particularly in the SI direction, which could result in compromise of target coverage when planning with a single free-breathing 4D-CT.
