Stereotactic Ablative Body Radiotherapy (SABR) for Oligometastases

Inclusion Criteria:

* Able to provide informed consent
* Histologically confirmed malignancy with metastatic disease detected on imaging.

  * Biopsy of metastasis is preferred, but not required.
* Primary tumour treated radically or controlled by prior palliative radiotherapy or systemic therapy
* Maximum 5 metastases eligible for SABR (either 5 in total or 5 not controlled by prior treatment)
* Standard of care tests prior to SABR CT simulation within 14 weeks:

  * Brain CT or MRI imaging (for tumour sites with propensity for brain metastasis)
  * Body imaging:
* CT chest/abdomen/pelvis, with or without bone scan (at discretion of study doctor), required if no PET-CT is performed
* PET-CT or PSMA-PET is only required for specific evidence-based indications, and in such cases the CT neck/chest/abdomen/pelvis and bone scan are not required:
* MRI spine for patients with vertebral or paraspinal metastases

  * For other indications, at the discretion of the treating oncologists, e.g. PET-CT scans may be done but are not required.
  * Blood tests as per standard of care
  * Pregnancy test for women of child-bearing age
* ECOG performance status 0-2
* All sites of progressive disease can be safely treated based on criteria below
* For non-brainstem mets, maximum size of 3cm if using single fraction radiosurgery.

  * If size is from 3.1 to 4cm, 25-35Gy/5 can be considered
* All brain metastases cases need approval from Stereotactic Radiosurgery (SRS) rounds

  * Maximum size of 6 cm for lesions outside the brain, except:
* Bone metastases over 6 cm may be included, if in the opinion of the local PI it can be treated safely (e.g. rib, scapula, pelvis)
* Life expectancy \> 6 months

  * In many scenarios, this is best estimated by a multidisciplinary opinion from disease site experts, often obtained by presentation at multidisciplinary tumours rounds.
* Not a candidate for surgical resection at all sites: surgery to all sites not recommended by multidisciplinary team, or unfit or declining surgery.
* No chemotherapy agents (cytotoxic, or molecularly targeted agents) will be used within the period of time commencing 2 weeks prior to radiation, lasting until 1 week after the last fraction. Certain chemotherapy agents may require a longer break prior to or after SABR if protocols dictate. Hormonal therapy during SABR is allowed.
* Patients with metastases that have been previously treated may be eligible for this SABR protocol:

  * If the previous treatment was systemic therapy, the patient may be eligible, if the metastases have demonstrated a complete radiologic response
  * If the previous treatment was by a local non-radiation means (e.g. prior resection, RFA or microwave ablation), then SABR may be considered for residual/recurrent disease
  * If the previous treatment was SABR, the patient is not eligible unless the new site(s) was/were not previously treated
* If the previous treatment was conventional RT, SABR could be considered if it can be delivered safely. In such a circumstance it must be presented in a multidisciplinary setting for approval.
* Review and consensus by 3 disease site experts, or tumour group conference, for eligibility/prognosis Patients must be able and willing to complete quality of life questionnaires in English, and other assessments that are a part of this study, via paper or online using REDCap (if email address is provided by participant on the informed consent) Note: The potential treating SABR radiation oncologist reserves the right to require a multidisciplinary note documenting life expectancy, other treatment options and suitability for SABR.

Exclusion Criteria:

* Serious medical co-morbidities precluding radiotherapy
* Bone metastasis in a femoral bone if risk of pending fracture is high
* Participants with 1-3 brain metastasis and no disease elsewhere (these participants should not be accrued but treated with stereotactic radiotherapy as per results of published randomized trials)
* Complete response to first-line chemotherapy (i.e. no measurable target for SABR)
* Persistent malignant pleural effusion
* Inability to treat all sites of active disease with ablative intent
* Clinical or radiological evidence of spinal cord compression
* Dominant brain metastasis requiring surgical decompression
* a candidate for a clinical trial that randomizes between SABR and a standard treatment
* Pregnant or lactating women