COLLISION XL: Unresectable Colorectal Liver Metastases (3-5cm): Stereotactic Body Radiotherapy vs. Microwave Ablation

Inclusion Criteria:

* 1-3 unresectable CRLM size 3-5 cm eligible for both MWA and SBRT (target lesions);
* Additional CRLM are allowed if considered either resectable or ablatable and \<3cm
* No or limited extrahepatic disease (1 extrahepatic lesion is allowed, not including positive para-aortal lymph nodes, celiac lymph nodes, adrenal metastases, pleural carcinomatosis or peritoneal carcinomatosis);
* For subjects with liver only disease the maximum number of CRLM is 10; for subjects with limited extrahepatic disease the maximum number of CRLM is 5;
* Prior focal liver treatment is allowed
* Subjects without prior focal liver treatment should be either unsuitable for 1st line chemotherapy or have progressed under/after 1st-line chemotherapy;
* Subjects with recurrent (either local or distant-hepatic) CRLM after previous focal treatment should be unsuitable for (further) systemic therapy (further downsizing or conversion to resectable disease improbable).

Exclusion Criteria:

* Compromised liver function (e.g. signs of portal hypertension, INR \> 1,5 without use of anticoagulants, ascites);
* Pregnant or breast-feeding subjects;
* Immunotherapy ≤ 6 weeks prior to the procedure;
* Chemotherapy ≤ 6 weeks prior to the procedure;
* Severe allergy to contrast media not controlled with premedication.