Inclusion Criteria:  Patients with HCC based on classical radiologic findings as defined by the American Association for the Study of Liver Diseases (AASLD) criteria or verified by biopsy No extra-hepatic disease Deemed ineligible for resection or Radiofrequency Ablation (RFA), or the patients should refuse RFA or surgery Age ≥ 18 years Performance status ≤ 2 Total diameter of tumor(s) ≤ 12 cm and a maximum of 3 tumors Adequate liver function as measured by Child-Pugh score (Child-Pugh score ≤ 8), or absence of cirrhosis Has recovered adequately from toxicity and/or complications from any previous local interventions Patients with past or ongoing hepatitis C infection are allowed, but treatment for hepatitis C must have been completed one month before study entry Patients with hepatitis B infection is allowed if antiviral therapy have been given for at least 4 weeks and Hepatitis B Virus (HBV) viral load is less than 100 IU/ml. The active therapy must continue throughout the radiation therapy. Patients who are Total hepatitis B core antibody (anti-HBc)(+), negative for Hepatitis B surface antigen (HbsAg) and negative or positive for Hepatitis B surface antibody (anti-HBs) with a HBV viral load under 100 IU/mL do not require HBV anti-viral prophylaxis  Adequate organ function  hematological: hemoglobin ≥ 6 mmol/l, absolute neutrophil count (ANC) ≥ 1,5 x 109/L, platelets ≥ 50 x 109/L hepatic: bilirubin ≤ 1.5 x ULN, alanin-aminotransferase (ALAT) ≤ 1.5 x ULN renal: creatinine ≤ 1.5 x ULN Ability to adhere to procedures for study and follow-up Signed informed consent to participate Final decisions on inclusion and treatment with proton therapy are at the discretion of the investigator  Exclusion Criteria:  Previous x-ray-based radiotherapy in the liver Child Pugh score >8 Tumor less than 1 cm from any critical organs at risk (OAR) (duodenum, kidney, stomach, intestines). Previous Selective internal radiation therapy (SIRT) Episode of hepatic encephalopathy within the last 6 months Uncontrolled ascites with need for drainage > 1 per month Episode of bleeding esophageal varices within the past month. If active bleeding from esophageal varices has occurred, a gastroscopy should be performed 4 weeks after the bleeding episode to ensure maximum grade 1 varices. Patients with metal implants where beam entrance through the metal implants cannot be avoided (not applicable for fiducial markers implanted for radiotherapy use) Patients for whom it is not possible to produce a robust treatment plan following the technical guidelines (Appendix A) Patients for whom it is not possible to implant fiducial markers e.g. due to insufficient coagulation of the blood.