Purpose: Radiation-induced liver disease is the problem for liver radiotherapy. We have developed the 4DCT-based elasticity map and consider integrating the elasticity map into treatment planning. The purpose of this study is to evaluate the relationship between dosimetric metrics of functional liver based on the elasticity map and serum biomarkers of liver function.
Methods: Twenty patients who underwent radiotherapy for liver were enrolled in this study. All patients were performed 4DCT scan for whole liver. Deformable image registration was performed using CT images at end-exhalation and end-inhalation and deformable vector field (DVF) was acquired. Liver elasticity was calculated using DVF and finite element method. Functional liver regions were defined four categories using calculated liver elasticity (1) 5.00 kPa (2) 4.00 kPa (3) 2.93 kPa (4) whole liver. For all treatment planning, the prescribed dose was recalculated equivalent dose in 2 Gy fraction (EQD2). The relationships between dosimetric metrics (Mean, V5, V10, V20, V30Gy) for each functional liver, variation of aspartate aminotransferase to platelet ratio index (APRI) and fibrosis-4 index (FIB-4) were evaluated.
Results: Functional liver regions could be classified based on the elasticity map. The mean functional liver volumes were 634.46, 274.77, and 120.00 cc for 5.00, 4.00 and 2.93 kPa, respectively. The means of the variation of APRI and FIB-4 were 0.49 and 2.85. For the anatomical liver region, all dosimetric parameters for functional liver were low or moderately correlated with APRI (R: 0.45-0.55) and FIB-4 (R: 0.36-0.54).For the functional liver region ≦ 2.93 kPa, all dosimetric parameters for functional liver were highly or moderately correlated with APRI (R: 0.66-0.81) and FIB-4 (R: 0.52-0.71).
Conclusion: We have developed the loadmap to integrate the elasticity map based on the 4D-CT for radiotherapy treatment planning. That may be helpful for functional liver radiotherapy in clinical practice and deserves further analysis.
Funding Support, Disclosures, and Conflict of Interest: Japan society for the promotion of science (JSPS) KAKENHI Grant number 20K16789(KF), 18K07753(TS)