Brain metastases occur in 20% to 40% of all patients with cancer and generally associated with a poor prognosis. In present, whole brain radiation therapy (WBRT), surgical resection and stereotactic radiosurgery (SRS) are widely used for treatment of metastatic brain lesion and many physicians recommended WBRT for multiple brain metastases.

     However, because WBRT could be underwent only once in one patient and with development of medical science, many patient with brain metastasis survive much longer than past, some patients need SRS for multiple metastatic brain lesions, even more than 15 lesions. Therefore, we analyzed treatment results of SRS for brain metastasis and try to know whether SRS is effective in even more than 15 metastatic brain lesions.

     Form October 2005 to October 2008, 323 patients were underwent SRS for metastatic brain lesions using Gamma-Knife type C or Perfexion® in our institution. The patients were divided into 4 group according to number of lesions which is visible on magnetic resonance imaging (MRI); group 1(1-5 lesions), group 2 (6-10 lesions), group 3 (11-15 lesions) and group 4 (more than 16 lesions).

     We analyzed the patients’ survivals, progression free survivals including local and distant failure, and other prognostic factors retrospectively. Statistical significance was indicated by a P value < 0.05. SPSS Version 13.0 software (SPSS, Chicago, IL) was used for statistical analysis.

     The patients consisted of 172 males and 151 females and mean age at SRS was 59 (30-89) years. Overall mean survival time after SRS is 16.5 (14.6-18.3) months. Mean survival times of each groups was showed as; group 1 (n=221): 17.0 months, group 2 (n=58): 15.5 months, group 3 (n=14): 17.6 months and group 4 (n=30): 11.3 months. There was no statistical difference of survival times after SRS between groups (Log Rank p=0.554). The probability of development of new lesion in brain was more in group 4. Mean time to distant failure in group 4 (7.6 months) is statistically shorter than that of other groups; group 1: 18.6 months, group 2: 15.5 months, and group 3: 19.8 months (p=0.014). However, the probability of local failure is no different statistically between each group.

     This is a retrospective study.

     In our series, patients with more than 15 metastatic brain lesions showed shorter duration to development of new lesion in brain. It may due to biological properties of patients’ primary lesion example for having a more tendency to disseminate hematogeneously, especially to brain, or higher probability of missed or invisible (microscopic metastasis) lesions to treat on stereotactic MRI. However, mean survival time after SRS is not different statistically between each group.

     With above results, we can suppose that despite patients with multiple metastatic brain lesions more than 15 may have early and easily new metastatic lesions, SRS could be a good treatment option for local control of metastatic lesions and improving survival of patients with multiple metastatic brain lesions.