In this study, the investigators aim to determine the dose-effect relationship between radiation dose and liver function by performing a hepatobiliary scintigraphy (HEBIS) before and after stereotactic body radiotherapy (SBRT) for patients with liver metastases. HEBIS is a nuclear imaging technique to quantitatively assess liver function. It better predicts the risk of postsurgical liver failure compared to volumetry alone. To prevent liver failure after SBRT, current clinical dose constraints require that ≥ 700 ml of normal liver should receive less than 15 Gy in 3 fractions. The exact local dose-effect relation is however unknown. Doses below 15 Gy are still damaging, while liver tissue receiving doses above 15 Gy will retain some function. By associating the 3D radiation dose distribution with the HEBIS scan, the investigators can evaluate the impact of radiation dose on liver function for different dose levels in liver (sub)volumes. This analysis will refine existing dose-effect relationships, enabling more tailored treatment of liver metastases in the future. Ten to fifteen patients will be included to assess functional liver imaging using HEBIS before their treatment and 3 to 4 months after their treatment.

Inclusion Criteria:

• Patient treated for a liver metastasis with SBRT with treatment prescription of 3 x 20 Gy
• Able to provide informed consent prior to any study specific procedure

Exclusion Criteria:

• WHO > 2
• Pregnancy
• Prior radiation therapy of the liver
• Lactation, unable to substitute for 24 hours
• Inability to cooperate with the scan process: inability to lie relatively still and in supine for 30-60 minutes or patient body habitus above scanner dimensions

Exclusion criteria for HEBIS scan:

• GFR < 30 ml/min/1.73m2
• < 2 weeks after antiviral eradication therapy for hepatitis C
• Bilirubine > 30 µmol/l
• Relative contra-indications (possibly affecting liver function): opiates, barbiturates, somatostatine, colestyramine, rifampicine, atropine

Ten to fifteen patients with a single liver metastasis who will be treated with SBRT, will be included to assess functional imaging using HEBIS before and 3-4 months after their treatment (SBRT). Patients are included in a single institute , NKI-AvL, in consecutive or convenient order.