The SOFT study will evaluate the feasibility and safety of MR-guided stereotactic ablative radiotherapy (SABR) for infra-diaphragmatic soft tissue metastases.

The investigators wish to evaluate the safety and feasibility of MR-guided stereotactic radiation to patients with infra-diaphragmatic oligometastatic disease including quality of life assessments and patient-reported outcome measures. Further, the investigators assess clinical response among patients with oligometastatic disease (OMD), defined as up to five metastases in up to three different organs.

Inclusion Criteria:

• Histology or cytology proven non-haematological cancer.
• At least one metastasis should be localized in the infra-diaphragmatic soft tissue.
• Eastern Cooperative Oncology Group (ECOG) scale of performance status ≤ 2.
• ≥ 18 years old.
• Life expectancy > 6 months.
• Target diameter (GTV) ≤ 5 cm.
• Metastatic lesions must be visible, imaging defined targets and suitable for treatment with SABR.
• In case of de novo OMD and oligometastatic recurrence a maximum of 5 targets (including the primary tumour) in a maximum of 3 organ sites are allowed.
• In case of oligoprogressive disease (OPD) * and induced OMD ** only 3 metastases (including the primary tumour) are allowed.
• 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 (PET-CT or CT and MR scanning).
• No curative intended treatment option available.
• An ablative strategy should be deemed clinically relevant and it is at the discretion of the treating physician to decide.
• Ability to understand and the willingness to sign a written informed consent document.
• If the target is in the liver, a Child-Pugh Score A is required.

Exclusion Criteria:

• Patient cannot tolerate physical set up required for SABR.
• Active bowel obstruction.
• Uncontrolled intercurrent illness.
• Medical contraindication to undergoing MR-imaging.
• Pregnancy.
• Patients with uncontrolled brain metastases.
• Uncontrolled disease in respect to malignant pleural effusion, ascites, lymphangitic carcinomatosis, pleural carcinomatosis or peritoneal carcinomatosis.
• If the patient has received previous radiotherapy, the combined dose at the radiation site must not exceed the dose constraints.