Present clinical practices of stereotactic irradiation for metastatic brain tumors in Japan: results of questionnaire survey of the Japanese Radiation Oncology Study Group (JROSG) working subgroup for neurological tumors

To determine the current practice of stereotactic irradiation (STI) for brain metastases in Japan by a questionnaire survey. A questionnaire was distributed to 313 institutions performing STI with one of the following machines: Gamma Knife (GK), CyberKnife (CK), Novalis (Nov), or other linear accelerator (LINAC)-based systems (OLS). The participation was voluntary. There were 163 responding institutions. The total number of STI treatments between April 2013 and March 2014 was 10,684. Stereotactic radiosurgery (SRS) and fractionated stereotactic radiotherapy (SRT) were performed in 8624 (80.7%) and 2060 (19.3%) cases, respectively. Whole-brain radiation therapy (WBRT) was performed for a total of 3515 cases. For a case model of a 1.5-cm solitary brain metastasis in a non-eloquent area, the most common GTV-PTV margin was 2 mm (22 of 114 institutions), and an institutional standard fraction was 1 (75 of 114 institutions). The doses for the model case also varied from 13.0 to 26.0 Gy (Median 20 Gy) when converted to SRS (α/β = 10). A prescription point was at the PTV margin the most. The median dose constraints which were converted to SRS (α/β = 3) to organs at risk were 12.2, 12.7, and 13.7 Gy for optic nerves, cavernous sinus, and brainstem, respectively. STI for brain metastases in current practice varied significantly among institutions. These different strategies relied mostly on the type of treatment machine used. It is thus necessary to establish a common guideline to express dose prescriptions and plan qualities for different STI machines.