A review article examined the latest utilization of PBT for hepatocellular carcinoma and cholangiocarcinoma, as well as liver metastasis. The dosimetric advantage of PBT over XRT in sparing uninvolved liver from low and moderate doses clearly translates into clinically meaningful benefit for some patients with liver cancer. PBT for HCC has been evaluated over several decades with low rates of toxicity and excellent long-term LC even in patients with large tumors.

Based on these outcomes, PBT receives the highest level of support (Group 1 recommendation) in the 2017 ASTRO Proton Beam Therapy Model Policy. For patients with intrahepatic cholangiocarcinoma and liver metastases, favorable tumor control, survival, and toxicity outcomes have been demonstrated after ablative PBT; however, additional research is needed to better understand the role of such therapy in the context of other liver-directed therapies. While the potential benefit from PBT for liver cancers, especially HCC, is largely undisputed, there is a lack of guidance about optimal patient selection for PBT. As such, identifying patient subgroups that are most appropriate for PBT should be a priority in future research.