Treatment Outcomes in Patients Receiving Carbon-Ion Radiotherapy Versus Hepatectomy for Hepatocellular Carcinoma (≥4 cm): A Retrospective Study in Japan

<b>Background/Objectives</b>: Carbon-ion radiotherapy (CIRT) is now covered by Japan's health insurance for patients with hepatocellular carcinoma (HCC) tumors measuring ≥4 cm. However, no studies have compared intrahepatic control between CIRT and hepatectomy in these patients. <b>Methods</b>: We retrospectively analyzed intrahepatic control in 51 patients with HCC tumors ≥4 cm. Among them, 38 underwent CIRT (60 Gy in four fractions), while 13 underwent systematic hepatectomy. Intrahepatic recurrence was classified as local or intrahepatic distant. We evaluated local, distant, and total intrahepatic control rates at 1 and 2 years. <b>Results</b>: In the CIRT group, the local control rates at 1 and 2 years were 81.5% and 76.3%, whereas the intrahepatic distant control rates were 68.5% and 63.2% (<i>p</i> = 0.0495), respectively. Among patients aged <80 years, the 2-year intrahepatic control rate did not significantly differ between CIRT and hepatectomy. However, it was significantly lower in patients aged ≥80 years treated with CIRT than in those aged <80 years (73.7% vs. 42.1%, <i>p</i> = 0.0100), with similar trends in local (92.3% vs. 63.2%, <i>p</i> = 0.0381) and distant control (78.9% vs. 47.3%, <i>p</i> = 0.0259). <b>Conclusions</b>: CIRT may be as effective as hepatectomy for HCC tumors ≥4 cm in patients aged <80 years, but its efficacy declines in older patients, warranting age-tailored strategies.