Stereotactic body radiation therapy for extracranial oligometastases: does the sword have a double edge?

Understanding the acute and chronic toxicities of stereotactic body radiation therapy (SBRT) for extracranial oligometastases might reveal treatment parameters that can be modulated to enhance the therapeutic ratio. Therefore, we searched PubMed from 1995 to 2005 for reports on stereotactic body radiation therapy, with emphasis on treatment of metastatic lesions of the lung and/or liver. Reports of SBRT for primary tumors of these sites were included to increase the number of evaluable patients. The reports were categorized by organ system and evaluated based on number of patients, number of lesions treated, dose fractionation scheme, and local control. A total of 15 lung studies (including 683 patients) and 7 liver studies (including 156 patients) were identified. Overall grade 3 to 5 toxicity was seen in up to 15% of patients in the lung SBRT studies and up to 18% of patients in the liver SBRT studies. Only 3 deaths were reported after SBRT of the liver and 2 after SBRT of the lung for treatment related mortality rates of 2% and 0.3%, respectively. No definitive relationship was found between radiation dose and toxicity. Conversely, radiation treatment volume may be associated with the infrequent toxicities that occur. The literature supports SBRT as a safe and effective treatment for oligometastases of the liver and lung. Further studies are needed to define the optimal dose and fractionation schedule.