Abstract
Regional based epidemiology of brain metastases was studied through the patients that were treated by gamma knife at the University of Minnesota. We reviewed 1903 procedures using Gamma Knife during the period from April 26, 2005 to June 29, 2010. Among them, 1172 (62%) cases were metastases. The most common types of metastases at our center, in descending order were lung, breast, skin and kidney. This matched well with medical data nationwide with the exception of breast metastases in women, which made up 44.5% in our group, higher than the national average. Taking into account the high accuracy of anatomical location required for stereotactic radiosurgery, we try to answer the question of whether metastatic lesions from specific sources are distributed according to the tissue volume of the region or by blood flow to the region. We use indices to represent the preference of certain tumors to metastasize to certain regions of the brain. An index of 1 signifies that the location of a metastasis strictly corresponds to the brain volume or the volume of regional blood flow. The bigger the brain volume, the more blood flow there is to the region. This increases the metastatic incidence, but not the index. Hence, a higher index indicates metastatic preference. The highest indices, >2 were found for small cell lung cancer (SCLC) in the cerebellum and brainstem, breast cancer in the cerebellum and renal carcinoma in the occipital lobe. These epidemiological data may help us to track the factors associated with lifestyle or the genomics involved in particular metastases. Understanding the metastatic preference may also give us further insight into the mechanisms of certain tumor proliferation and homing based on the different environments present in various parts of the brain.