Phase II Clinical Study to Ablate Oligometastatic Deposits by Single Dose Radiotherapy (SDRT) and Metabolic Assessment of Outcome

This phase II clinical trial is designed assess clinical outcomes following ablation by Single Dose Image Guided Radiotherapy (SDRT) in patients with oligometastatic (OM) presentation (1-5 clinically detectable lesions). For local tumor ablation the investigators will use the novel non-invasive and highly effective technique of SDRT which is capable of conferring long-term local relapse-free rates in approximately 90% of metastatic lesions independently of tumour histology. Historical series with various tumor histologies have shown subgroups of patients with an initial oligometastatic presentation respond to complete surgical removal of detectable deposits, yielding up to 20% disease-free survival at 10 years. The study will determine response rates by metabolic criteria (i.e. PERCIST). Pre- and post-treatment assessment are performed by FDG (or other appropriate PET tracer) PET/CT scans with acquisition of information on lesion(s) location, volume and metabolic parameters. Changes in metabolic avidity post treatment can be used to evaluate the rates of complete metabolic response, stable disease and progression at the site(s) of SDRT to measure local relapse-free survival intervals (LRFS and the kinetics of tracer uptake may serve as a potential predictive tool of treatment response). Additionally, whole-body PET/CT scans can be used to assess distant metastasis-free progression, polymetatstasis-free survival (PMFS). Lesions which are not amenable to the SDRT approach due to the inability to safely fulfill dose/volume constraints, are consistently treated with a hypofractionated approach of three sessions of 9Gy, an established and safe treatment regimen. Comparisons in LRFS, persistence of the oligometastatic status, distant metastasis free-survival, poly-metastasis-free survival, interval between repeat treatments and overall survival will be evaluated evaluated. The impact of systemic treatment, as per current established clinical practices, will also be assessed.