A Review of the Clinical Outcomes for Patients Diagnosed with Brainstem Metastasis and Treated with Stereotactic Radiosurgery

Only 3%–5% of all brain metastases are located in the brainstem. We present a comprehensive review of the clinical outcomes from modern studies that treated patients with brainstem metastasis using either a Gamma Knife or a linear accelerator-based stereotactic radiosurgery. The median survival time of patients was compared to better understand what clinical or treatment factors are predictive of improved survival. This information can then be utilized to optimize patient care. The data suggests that higher prescribed marginal dose and the associated greater local control of brainstem lesions are associated with longer patient survival. Further research is necessary to better describe the most effective dose for individual brainstem lesions and to tailor optimum therapy to specific patient subgroups. 1. Introduction Brain metastases travel via the vascular system to the brain [1], and 40% of patients diagnosed with systemic cancer will develop brain metastasis [2, 3]. Although the occurrence of BSM is relatively low (approximately 3%–5% of all brain metastasis cases), the prognosis for this subset is very poor [4]. Clinical reviews of patients treated for BSM report historical median survival times ranging from 1 to 11 months [5]. Furthermore, the delicate nature and location of the brainstem make it a difficult structure to treat. There is excessive morbidity from conventional neurosurgery and most chemotherapeutic agents are ineffective secondary to the blood-brain barrier. Whole-brain radiation (WBRT) therapy and stereotactic radiosurgery (SRS) (by Gamma Knife or linear accelerator [LINAC]) have proved to be effective treatment modalities for BSM [4–10]. In fact, for many patients diagnosed with BSM, radiation is the only viable treatment modality. Both LINAC and Gamma Knife treatments expose cancerous lesions to high energy X-rays in an attempt to cause irreversible damage to the DNA strands of the target cells and eventually cause cell death. The purpose of this paper is to review the clinical outcomes and survival statistics of patients diagnosed with brainstem metastasis who have been treated by these targeted radiation techniques. 2. Review Due to the difficulty and increased risk of treating BSM with conventional neurosurgery, treatment with radiation therapy (especially SRS) has become standard. We review and discuss twelve series published between 1999 and 2011. In each of these studies, patients were treated with SRS using either LINAC- or Gamma-Knife-based systems. 2.1. Survival As seen from Table 1, patients diagnosed with BSM have median