MRI Guided Adaptive Radiotherapy (MRgART) in Primary and Metastatic Liver Lesions

Abstract

The role of stereotactic body radiotherapy (SBRT) in the management of primary hepatic and metastatic tumors has increased significantly over the past few years. MR-Linac is rapidly gaining evidence in the delivery of ablative doses using MR guided adaptive radiotherapy (MRgART) with improved accuracy and dose coverage to the lesions. We report local control and toxicity of patients with primary and metastatic liver lesions treated with MR guided adaptive SBRT. All patients were treated with MRgART on the Unity 1.5T MR Linacs at two institutions and consented to the ADAPT-MRL study (1). A 4DCT and MRI with abdominal compression were obtained at simulation and the primary MRI sequence used for online treatment included a T2 3D navigated scan. A balanced turbo field echo (btFFE) 2D cine motion scan was also acquired at every fraction to determine movement of the tumor to aid in internal target volume margin. All plans were treated with SBRT prescribed to 3-5 alternate daily fractions. Acute toxicity was reported according to Common Terminology Criteria for Adverse Events version 5 (CTCAE) v.5. Patient demographics, prescribed dose fractionation, acute toxicity and clinical response at 6 months were analyzed. Clinical response to treatment was measured according to RECIST criteria 1.1. Between February 2021 to January 2023 a total of 30 patients were treated with 149 fractions to the liver. Patients were majority male (70%) with a median age of 66 (range 36-83). 16 patients were treated for primary hepatocellular carcinoma (HCC) of the liver and 14 patients for metastatic liver lesions. The median prescribed dose was 48 Gy (range 30-50Gy) in median 5 fractions (range (3-5 fractions). All patients completed treatment with no interruptions. The mean time from 'patient setup' to 'beam-off' was 52.6 minutes (range 37-73 minutes). Data on acute toxicity at 3 month follow up was available for 28 patients. Of these patients 7/28 (25%) had grade 1 or 2 toxicity and no >/ = grade 3 toxicity was reported. Clinical response at 6 months was available for 18 patients and showed complete response in 44% (8/18), partial response in 22% (4/18), stable disease in 22% (4/18) and progressive disease in 11.1% (2/18). Our experience on MRgART to the liver has shown good local control and minimal acute toxicity in the treatment of primary and metastatic liver lesions. We continue to collect data on patient reported outcomes, clinical response and toxicity to determine the feasibility and safety of this system.