A multi-institutional experience of MR-guided liver stereotactic body radiation therapy

Abstract Purpose/Objectives Daily MR-guided radiation (MRgRT) has the potential to improve stereotactic body radiotherapy (SBRT) for tumors of the liver. MRI introduces unique variables untested clinically: electron return effect, MRI geometric distortion, MRI to RT isocenter uncertainity, MLC position error, and uncertainties with voxel size/tracking. All of these could lead to increased toxicity and/or local recurrences with SBRT. In this multi-institutional study, we hypothesized that direct visualization provided by MR-guidance could allow the use of small treatment volumes to spare normal tissues while maintaining clinical outcomes despite the aforementioned uncertainties in MR-guided treatment. Materials/Methods Patients with primary liver tumors or metastatic lesions treated with MR-guided liver SBRT were reviewed at three institutions. Toxicity was assessed using CTCAEv4. Freedom from local progression (FFLP) and Overall Survival (OS) were analyzed with Kaplan-Meier method and chi-square test. Results The study population consisted of 26 patients: 6 hepatocellular carcinomas (HCC), 2 cholangiocarcinomas, and 18 metastatic liver lesions (44% colorectal metastasis (CRM)). The median follow-up was 21.2 months. The median dose delivered was 50 Gy at 10 Gy/fraction. No Grade 4 or greater GI toxicities were observed after treatment. The 1-year and 2-year OS in this cohort is 69% and 60%, respectively. At the median follow-up, FFLP for this cohort was 80.4%. FFLP for patients with HCC, CRM, and all other lesions were 100%, 75%, and 83% respectively. Conclusions This study describes the first clinical outcomes of MR-guided liver SBRT. Treatment was well tolerated by patients with excellent local control. This study lays the foundation for future dose escalation and adaptive treatment for liver based primary malignancies and/or metastatic disease.