Functional avoidance liver 4π-SBRT informed by quantitative Gadoxetic-acid contrast-enhanced MR T1 mapping.

Abstract

Purpose: Recent studies have identified the T1 reduction rates (k1) from Gadoxetic acid-enhanced magnetic resonance imaging (MR) as a biomarker for liver function. In this study, we validate k1 maps as a functional biomarker and develop 4π noncoplanar treatment plans using k1 maps to guide the optimization for liver functional avoidance stereotactic body radiation therapy (FA-SBRT).

Methods: 106 patients underwent pre- and post-contrast T1 mapping MR. Mean liverGTV k1 values were correlated with Child-Pugh (CP) and ALBI scores. The highfunction (HF) liver region was identified and masked using a patient-specific threshold from Gaussian decomposition of the k1 histogram. Twenty patients were retrospectively planned with coplanar and non-coplanar 4π-SBRT with and without functional avoidance. Tumor coverage was maintained at a minimum of 90% PTV to receive prescription, and standard OAR constraints were set for all plans. Dose metrics included mean dose to the HF liver and HF liver volume receiving 6 Gy, which was shown to impact patient liver function. A paired, two-tailed t-test was used to determine the statistical significance.

Results: k1 values were inversely correlated with CP and ALBI. The 4π FA-SBRT plans reduced the mean dose to the high-function liver volume by 21.8% (from 9.2 Gy to 6.5 Gy) (p<.0001) and the volume of high-function liver receiving > 6 Gy by 39.5% (from 507.5cc to 302.2cc) compared with the 20-beam coplanar geometry (p<.0001). All reductions were statistically significant (p<.01).

Conclusion: This study validates k1 derived from free-breathing T1 mapping MR as a liver function biomarker in a cancer patient cohort. Gaussian decomposition can threshold the k1 distribution to create patient-specific HF liver masks. The 4π FA SBRT planning guided by k1 maps significantly reduced the mean dose to the HF liver, as well as the volume of HF receiving >6Gy.