This is a prospective, investigator-initiated, phase II, multicentre-study, investigating the efficacy and toxicity of definitive SABR of osseous oligometastases, when pragmatically introduced into a daily clinical setting.

Patients with a histology or cytology proven non-hematological cancer and at least one lesion in the bones are eligible.

Patients with de novo- and induced oligometastatic disease, as well as patients with oligo-recurrence or oligo-progression disease can be included. A total of 67 patients will be enrolled.

The overall aim is to document long time follow-up in respect to local control rate, OS, PFS, rate of symptomatic skeletal event at the irradiated site(s), time to progression outside the radiation field at 1-, 2- and 5-years and acute/ late toxicities.

The primary endpoint is the rate of local control 1-year post SABR. Patients will have a CT scan and a clinical evaluation every 3 month after SABR according to the standard clinical follow-up program.

During the 1 year follow-up we also perform pain assessment (using the Numeric Pain Rating Scale), report the analgesic consumption and Quality of life (QoL) measured with EQ-5D-5L.

Two dose levels are offered with either 37.5 gy in 3 fractions or 30 gy in 3 fractions, prescribed to the GTV.

Inclusion Criteria:

• Histology or cytology proven non-haematological cancer.
• At least one lesion in the bones is required.
• ECOG performance status ≤ 2.
• ≥ 18 years old.
• Life expectancy > 6 months.
• GTV diameter ≤ 5 cm.
• In case of de novo OMD and OMD recurrence a maximum of 5 targets (including the primary tumour) in a maximum of 3 organ sites are allowed.
• In case of OPD * and induced OMD*2 only 3 metastases (including the primary tumour) are allowed.
• The metastatic lesion(s) must be visible on a CT- or MR- scan and suitable for treatment with SABR.
• All metastatic sites are treated or planned for ablative therapy (including surgery) - for OPD only the sites in progression is required to fulfil this criterion. • A baseline scan within 28 days of inclusion (CT or PET- CT).
• For spine/paraspinal targets, an MR scan is mandatory, if epidural growth cannot be precluded on the baseline CT scan.
• No curative intended treatment option available.
• An ablative strategy should be deemed clinically relevant and is at the discretion of the treating physician to decide.
• Ability to understand and the willingness to sign a written informed consent document.

Exclusion Criteria:

• Patient cannot tolerate physical set up required for SABR.
• Uncontrolled intercurrent illness.
• Pregnancy.
• Bilsky score ≥ 1b. If the patient is treated with surgery, a pre-operative Bilsky score ≥ 1b is an exclusion criterion as well. See appendix A for Bilsky score.
• Presence of myelopathy from the target area.
• Candidate for surgical treatment (determined by the institutions clinical oncologist, neurosurgeon or orthopaedic surgeon).
• For spine/paraspinal lesions where epidural growth cannot be precluded on the baseline CT scan: patients for whom an MR scan is contraindicated.
• Mechanical instability and/or fracture risk *3.
• For spine disease, involvement of ≥ three contiguous vertebrae.
• Uncontrolled disease in respect to malignant pleural effusion, ascites, lymphangitic carcinomatosis, pleural carcinomatosis or peritoneal carcinomatosis.
• Patients with uncontrolled brain metastases.
• If the patient has received previous radiotherapy, the combined dose at the radiation site must not exceed the dose constraints according to Appendix B. -