A Study to Assess the Efficacy of Cerebellar IMRT Combined With Cerebral SRS in Patients With Brain Metastases

This study includes patients with brain metastases, presenting with more than 5 cerebellar lesions and less than 10 cerebral lesions. This is a pilot study assessing the efficacy of a novel, combined treatment approach involving Intensity-modulated Radiation Therapy (IMRT)/ Volumetric Modulated Arc Therapy (VMAT), with or without integrated boost to metastases, administered to the posterior fossa, and Stereotactic Radiosurgery (SRS) administered to cerebral lesions. This is opposed to the current recommended treatment approach for such cases, being whole brain radiotherapy (WBRT). While an effective treatment with respect to lesion control, WBRT is not ideal as the total deliverable dose is limited to 30 Gy due to toxicity. In addition, this technique is responsible for major side effects, especially neurocognitive deterioration. There are select cases of multiple brain metastases which are predominantly found in the posterior fossa. Rectal cancer is one such notorious example, however this type of spread is not limited to one region. The investigators hypothesize that utilizing the novel combinational treatment approach of IMRT and SRS in cerebral and cerebellar brain metastases will improve long term brain control, maintain the patients' cognitive function and potentially improve overall survival, as the need for potent WBRT will become obsolete. Patients with multiple brain metastases present in the cerebrum and cerebellum will be treated with SRS and IMRT respectively, simultaneously (within 3 weeks of one another). Brain MRI scans will be performed before commencement of the novel treatment approach, at two month after RT, and then every 3 months, or as indicated clinically, after treatment start. Concurrently at each MRI scan time point, patients will be assessed based on brain and whole-body metastatic progression by RECIST. Patients will also be assessed for central nervous system (CNS) - progression free survival (PFS) and body-PFS, cognitive function, quality of life and overall survival status via standardized follow-up tests.