SABR-SCAN Trial for Pulmonary Oligometastases

Inclusion Criteria: * Age ≥ 18 years * WHO-Performance status (WHO-PS) 0 - 1 * Patients with 1 to 3 lung metastases between 8 mm and 3 cm each, from colorectal cancer. Resection has been considered at a multidisciplinary conference but was not recommended or has been refused by the patient. * Possibility to define target lesions that fulfil the following criteria: * No lesion larger than 3 cm; * Not more than 3 metastases ≥ 8 mm in total (lesions smaller than 8 mm in diameter are NOT counted and will NOT be irradiated); * No prior radiotherapy (SABR or other) within about 2 cm from target lesions (i.e., the distance between prior planning-target-volume (PTV) to actual intended PTV is more than 2 cm AND dose distribution of former radiation permits SABR). * Primary tumour has been completely removed surgically. * Metastases outside target organs (e.g. liver metastases or other) are radically treated locally (resection, radiofrequency ablation (RFA), microwave ablation (MWA), stereotactic radiotherapy, or other). Earlier resected or ablated (SABR, RFA, MWA) metastases to lung, liver, or other organ form no exclusion criterion. Brain metastases should be completely resected or treated with stereotactic radiosurgery. Bone metastases should be resected or treated with high dose radiotherapy (equivalent of \> 40 Gy) and be asymptomatic. * Patients at reproductive potential must agree to practice an effective contraceptive method. Women of childbearing potential must not be pregnant or lactating. * Proficiency in the Dutch language so that quality-of-life questionnaires can be completed in Dutch and absence of any psychological, familial, sociological or geographical condition potentially hampering compliance with the study protocol and follow-up schedule; those conditions should be discussed with the patient before registration in the trial. * Before patient randomisation, informed consent must be given according to International Conference on Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human Use (ICH) of the European Union (EU) in accordance with good clinical practice (GCP), and national/local regulations. Exclusion Criteria: * Any clinical symptoms possibly or certainly caused by index lungmetastases * Physical inability to undergo stereotactic radiotherapy (e.g., serious shoulder stiffness) * Any uncontrolled malignancy other than index colorectal cancer * Other malignancy within recent two years, even if completely under control (under control = no evidence of disease) * Failure to comply with any of the inclusion criteria