Direct visualization and correlation of liver stereotactic body radiation therapy treatment delivery accuracy with interfractional motion.

This study used the visualization of hypo-intense regions on liver-specific MRI to directly quantify stereotactic body radiation therapy (SBRT) spatial delivery accuracy. Additionally, the interfractional motion of the liver region was determined and compared with the MRI-based evaluation of liver SBRT spatial treatment delivery accuracy. Primovist -enhanced MRI scans were acquired from 17 patients, 8-12 weeks following the completion of liver SBRT treatment. Direct visualization of radiation-induced focal liver reaction in the form of hypo-intensity was determined. The auto-delineation approach was used to localize these regions, and center-of-mass (COM) discrepancy was quantified between the MRI hypo-intensity and the CT-based treatment plan. To assess the interfractional motion of the liver region, a planning CT was registered to a Cone Beam CT obtained before each treatment fraction. The interfractional motion assessed from this approach was then compared against the localized hypo-intense MRI regions. The mean ± SD COM discrepancy was 1.4 ± 1.3 mm in the left-right direction, 2.6 ± 1.8 mm in an anteroposterior direction, and 1.9 ± 2.6 mm in the craniocaudal direction. A high correlation was observed between interfractional motion of visualized hypo-intensity and interfractional motion of planning treatment volume (PTV); the quantified Pearson correlation coefficient was 0.96. The lack of correlation was observed between Primovist MRI-based spatial accuracy and interfractional motion of the liver, where Pearson correlation coefficients ranged from -0.01 to -0.26. The highest random and systematic errors quantified from interfractional motion were in the craniocaudal direction. This work demonstrates a novel framework for the direct evaluation of liver SBRT spatial delivery accuracy.