Using Radiotherapy and Immunotherapy to Treat Advanced Liver Cancer Before Transplant

The goal of this clinical trial is to learn if locoregional therapy and immunotherapy can be used together to help patients with hepatocellular carcinoma (HCC) and macrovascular invasion achieve liver transplantation. The main questions it aims to answer are: * How many patients will achieve transplant with this treatment strategy? * What will the 5-year survival and recurrence-free survival rates be for these patients? Participants will: * Undergo a biopsy of the tumor. * Receive locoregional therapy (SBRT or Y90) followed by immunotherapy (atezolizumab and bevacizumab) 2 to 6 weeks later, for a maximum of 9 months. * Be referred for a liver transplant and undergo the procedure if deemed eligible and safe. * If applicable, be followed for five years post-transplant with regular data collection.