Radioembolization is an established treatment option for patients with unresectable primary and secondary liver tumors. Microspheres containing 90Y are injected intraarterially to deliver a high radiation dose to the tumors. Despite of our knowledge on the effectiveness of 90Y glass microspheres in the treatment of HCC, literature data on the treatment of metastatic colorectal cancer (mCRC) patients with 90Y glass microspheres is limited. In the recent EANM guideline variable healthy liver doses are recommended for patients with mCRC with an effective tumor dose recommendation based on a study with limited number of patients.

Primary objectives; Investigate effective tumor dose and safe healthy liver dose in radioembolization for colorectal cancer liver metastasis using multicompartment dosimetry Secondary objectives; Investigate dose-response and dose-toxicity relationships, time to progress, concordance between pretreatment and posttreatment dose calculations.

Inclusion Criteria:

• over 18 years old
• histopathologically proven colorectal cancer diagnosis
• treated with radioembolization for liver metastases with Y90 glass microspheres in lobar or segmental fashion
• have follow-up data at least 6 months after radioembolization

Exclusion Criteria:

• no PET-CT, CT or MR of the liver within last 6 weeks prior to radioembolization.

No PET-CT, CT or MR of the liver 2-4 months after radioembolization Poor image quality Previous local treatment or surgery for the liver

Adult patients with metastatic colorectal cancer (mCRC) treated using Y90 glass microspheres in lobar or segmental fashion