Hepatic reaction dose for parenchymal changes on Gd-EOB-DTPA-enhanced magnetic resonance images after stereotactic body radiation therapy for hepatocellular carcinoma

Introduction The present study evaluated the threshold dose for hepatic parenchymal changes on gadolinium ethoxybenzyl diethylenetriaminepentaacetic acid (Gd-EOB-DTPA)-enhanced magnetic resonance (MR) images after stereotactic body radiation therapy (SBRT) for hepatocellular carcinoma (HCC). Methods Twenty patients with available data of follow-up MR images acquired 2–4 months after completion of SBRT were selected among the registered patients. SBRT was performed using multiple coplanar and non-coplanar beams with energies of 6 or 15 MV. All patients were treated with doses of 45 Gy administered in three fractions over 3 consecutive days. For image registration between planning computed tomography (CT) and MR images, landmark-based rigid body registration was performed using MIM software. Results Seventeen patients were included in the analysis. The median discrepancies between planning CT and MR images in the left–right, anterior–posterior and superior–inferior directions were 1.38 mm, 1.24 mm and 1.72 mm, respectively. The median D50 value for the defect in the hepatobiliary phase of Gd-EOB-DTPA-enhanced MR images after SBRT was 19.8 Gy (range, 14.2–28.7 Gy), with R2 values ranging from 0.76 to 0.99. Conclusions The threshold dose for parenchymal changes in the hepatobiliary phase of Gd-EOB-DTPA-enhanced MR images performed 2–4 months after 45 Gy of SBRT in three fractions was approximately 20 Gy. Our results provide the basis for further research on the functional loss of liver parenchyma after SBRT.