Function-Guided Planning In Liver SBRT Using Gadoxetic Acid–Enhanced MRI
Abstract
Purpose
To evaluate the dosimetric benefit of incorporating MR-based functional dose objectives into liver stereotactic body radiation therapy (SBRT) planning.
Methods
Fourteen patients with hepatocellular carcinoma (HCC) treated with SBRT underwent dynamic gadoxetic acid–enhanced liver MRI as part of an IRB approved treatment protocol. Voxel-based gadoxetic acid uptake rate (k1) maps were generated and registered to planning CT images. High-function liver was defined as voxels with k1 values exceeding 10% of the maximum hepatic function, across all patients, and contoured as a high-function region. Function-guided plans were retrospectively generated by introducing additional optimization constraints to limit the volume of high-function liver receiving ≥5 EQD2Gy and ≥15 EQD2Gy. Plan quality was evaluated by comparing planning target volume (PTV) coverage (D95% and D99%), functional DVH metrics (k1 V5EQD2Gy and k1 V15EQD2Gy), and mean physical and equieffective doses to high-function liver between function-guided and clinical plans. Paired comparisons were performed using the Wilcoxon signed-rank test.
Results
Compared to standard clinical planning, function-guided planning resulted in measurable reductions in dose to functional liver regions. On average, k1 V5EQD2Gy and k1 V15EQD2Gy decreased by 8.4% and 7.8%, respectively, and the mean dose to high-function liver volume was reduced by 2.2 EQD2Gy. All functional dose metrics showed statistically significant improvement, with the largest effect observed for k1 V15EQD2Gy (p < 0.001). Target coverage was largely preserved, with only minimal reductions of 0.8% in PTV D95 and 1.0% in D99, both remaining within clinically acceptable limits.
Conclusion
This study demonstrates the dosimetric impact of incorporating gadoxetic acid–based functional mapping and MRI-derived functional dose metrics into liver SBRT planning. Function-guided optimization enables patient-specific sparing of high-function liver tissue with minimal changes in target coverage, supporting further development of predictive models to identify patients most likely to benefit from functional liver–guided SBRT.