SU‐G‐206‐16: Investigation of Dosimetric Consequence Via Cone‐Beam CT Based Dose Reconstruction in Hepatocellular Carcinoma Radiotherapy

Abstract

Purpose:Many patients with technically unresectable or medically inoperable hepatocellular carcinoma (HCC) had hepatic dosimetric variations as a result of inter‐fraction anatomical deformation. This study was conducted to assess the hepatic dosimetric consequences via reconstructing weekly dose in HCC patients receiving three dimensional conformal radiation therapy.Methods:Twenty‐one HCC patients with 21 planning CT (pCT) scans and 63 weekly Cone‐beam CT (CBCT) scans were enrolled in this investigation. Among them, six patients had been diagnosed of radiation induced liver disease (RILD) and the other fifteen patients had good prognosis after treatment. And each patient had three weekly CBCT before re‐planning. In reconstructing CBCT‐based weekly dose, we registered pCT to CBCT to provide the correct Hounsfield units for the CBCT using gradient‐based deformable image registration (DIR), and this modified CBCT (mCBCT) were introduced to enable dose calculation.To obtain the weekly dosimetric consequences, the initial plan beam configurations and dose constraints were re‐applied to mCBCT for performing dose calculation, and the mCBCT were extrapolated to 25 fractions. Besides, the manually delineated contour was propagated automatically onto the mCBCT of the new patient by exploiting the deformation vectors field, and the reconstructed weekly dose was mapped back to pCT to understand the dose distribution difference. Also, weekly dosimetric variations were compared with the hepatic radiation tolerance in terms of D50 and Dmean.Results:Among the twenty‐one patients, the three weekly D50 increased by 0.7Gy, 5.1Gy and 6.1Gy, respectively, and Dmean increased by 0.9%, 4.7% and 5.5%, respectively. For patients with RILD, the average values of the third weekly D50 and Dmean were both high than hepatic radiation tolerance, while the values of patients without RILD were below.Conclusion:The planned dose on pCT was not a real dose to the liver, and the liver overdose increased the risk of RILD.The author would like to express great thanks to Lei Xing, Daniel S Kapp and Yong Yang in the Stanford University School of Medicine for their valuable suggestions to this work. This work is supported by NSFC(61471226), China Postdoctoral Science Foundation (2015T80739,2014M551949) and research funding from Shandong Province (JQ201516).