Comparative Assessment of Liver Tumor Motion Using CineMRI Versus 4DCT

Abstract

Accurate radiation therapy (RT) targeting of hepatic tumors is critically dependent on organ and tumor motion assessment, most commonly performed with 4DCT. Since 4DCT captures only a snapshot of tumor motion in time and is prone to artifacts and irregular breathing, it is unclear how reliable 4DCT is in determining intra-fraction tumor motion. CineMRI allows for prolonged real-time organ and tumor motion assessment with no radiation exposure. We compared the extent of tumor motion between 4DCT and cineMRI in patients with hepatic tumors treated with RT. Ten patients with hepatocellular carcinoma (n = 6), cholangiocarcinoma (n = 3), and liver metastasis (n = 1) underwent 4DCT and 2D biplanar cineMRI scans during simulation to determine the extent of target motion in the superior/inferior (S/I), anterior/posterior (A/P) and lateral directions. CineMRI was performed over 5 minutes. Tumor motion was determined by the changes in centroid position of the gross tumor volume (GTV) as determined by deformable contour propagation. Margins were determined by using histograms of 90% confidence interval of GTV motion in each direction. Motion estimates from 4DCT was performed by evaluation of the marker positions in each phase of the CT. We compared the extent of GTV motion and resulting margin size between cineMRI and 4DCT. The difference in A/P margin and lateral motion between the 4DCT and cineMRI was minimal (Table). The S/I margin was underestimated by 4DCT in 8/10 patients by a mean of 3.4 mm (range, 1.5-7 mm). The average inferior motion (median to 10th percentile) was of greater magnitude (6.2 mm vs 4.2 mm) compared to the average superior motion (median to 90th percentile). Superior, inferior, lateral, anterior, and posterior margins of 6, 8, 3, 5, and 3 mm respectively would be needed to cover 90% of the intra-fraction GTV motion as defined by cineMRI. CineMRI detects differences in hepatic intra-fraction tumor motion when compared to 4DCT, most notably in the S/I direction. When treating without respiratory management, caution should be taken when determining tumor margin as 4DCT can underestimate target motion, particularly in the S/I direction. Asymmetric margins as mentioned above should be considered to account for intra-fraction hepatic tumor motion.Oral Scientific Abstract 108; TableComparative Assessment of Liver Tumor Motion Using CineMRI Versus 4DCTMean/Median Cine-MRI motion (range), mmMean/Median 4D-CT motion (range), mmMotion difference (range), mmSuperior-Inferior10.4/9.8 (6-18)7.7/7.5 (4-12)2.7 (-0.5-7)Anterior-Posterior5.6/4.8 (2.2-15.5)4.9/4.0 (2-7.5)0.7(-1.8-5.5)Lateral2.8/2.4 (1-4.5)2.3/2.0 (0-6)0.5 (-2-2.5) Open table in a new tab