Increased pyruvate-to-lactate conversion is a hallmark of HCC metabolism. In parallel, activation of pro-inflammatory immune cells triggers a metabolic switch towards anaerobic glycolysis. Hyperpolarized carbon-13 (13C) pyruvate MRI is a state-of-the-art non-invasive imaging method that offers real-time insights into tissue metabolism. Recent studies have demonstrated its promising potential in predicting responses to radiotherapy and immunotherapy in solid tumors, given the significance of pyruvate as a downstream metabolite in glycolysis. However, its application in assessing treatment response in hepatocellular carcinoma (HCC) patients remains unclear. The establishment of quantitative imaging biomarkers for predicting responses to radio-immunotherapy is an unmet need in the management of HCC patients. While radiotherapy (RT) effectively controls localized tumors through the induction of unrepairable DNA double-stranded breaks (DSBs) and cell death, its therapeutic efficacy on distal, non-irradiated tumor cells is limited, with out-of-field recurrence being a common pattern of failure in HCC patients treated with high-dose irradiation. Atezolizumab (anti-programmed death-ligand 1; anti-PD-L1) in conjunction with bevacizumab (anti-vascular endothelial growth factor; anti-VEGF) has recently emerged as the standard first-line systemic treatment for unresectable hepatocellular carcinoma (HCC). Despite an objective response rate (ORR) of only 27%, the majority of patients succumb to HCC progression and liver failure. Our preclinical study (Hsieh et al., Science Immunology 2022) uncovered that RT, when combined with PD-L1/PD-1 blockade, induces immunogenic cell death and tumor antigen cross-presentation in antigen-presenting cells, enhancing systemic antitumor T cell responses in murine tumor models. Recent retrospective cohorts suggest that RT targeting all hepatic tumors combined with PD-L1/programmed death-1 (PD-1) blockade is associated with an improved ORR and median progression-free survival (PFS) in patients with unresectable HCC, demonstrating a favorable safety profile. The synergistic antitumor effects of this combination therapy with RT, atezolizumab, and bevacizumab have led to its increasing adoption in routine clinical practice. This phase II non-randomized trial aims to prospectively investigate the predictive value of hyperpolarized 13C-MRI, along with comprehensive metabolomics and radiomics analyses, for immune response assessment including tumor control outcomes and toxicity in patients with HCC undergoing radiotherapy, atezolizumab, and bevacizumab.