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instead of an invasive fixation using a head pin. The LINAC systems used the Elekta Synergy plat-form (Elekta AB, Stockholm, Sweden), with IGRT, 6-degree robotic couch (HexaPOD)6), and 3 mm micro multi-leaf to maintain the fixation accuracy below 1 mm. HexaPOD (Elekta AB, Stockholm, Sweden) is a couch that can adjust the twisting element in addition to the XYZ position, and is a system with higher accuracy than the 3-axis couch. SRS using HexaPOD was started for the first time in Japan. Many cases have been treated with acceptable accuracy using this system7).SRS with the latest LINAC systemsIn general, 80% of SRS cases comprise brain metastases. Until around 2014, whole-brain irradia-tion was indicated for three to four or more brain metastases. However, in recent years, the advent of molecular targeted drugs has enabled long-term survival of patients even in advanced cancer stages. In such an era background, in recent years, cogni-tive decline as an adverse effect of whole-brain irradiation has become a problem.Furthermore, the results of a multicenter joint study by the Gamma Knife group1) have offered a choice to perform SRS on patients with multiple brain metastases. In 2021, the LINAC systems of the Juntendo Nerima Hospital were updated to the latest model called Versa HD (Elekta AB,Stock-holm, Sweden) (Figure 6). Versa HD is a highly versatile Linac capable of stereotactic radio surgery (SRS) for multiple brain tumors and high-defini-Figure 6　New Linac systems in Juntendo Nerima Hospital (Versa HD by Elekta corption volumetric modulated arc therapy (VMAT)8). It is possible to obtain not only online marker-less 4D-Cone Beam CT (CBCT), but also 3D / 4D CBCT during treatment. Moreover, the treatment time is shorter than that of conventional SRS. Furthermore, the treatment accuracy has an error of 1 mm or less by using a quality control system called Catalyst (C-RAD Positioning AB, Uppsala, Sweden). Although it has become possible to perform SRS for multiple brain metastases using this systems, it is necessary to consider the indica-tion of SRS based on the patient background. An example of SRS for multiple brain metastases is presented in Figure 7. Since this patient had a history of prophylactic whole-brain irradiation due to small-cell lung cancer, it was impossible to re-ra-diate the whole brain. Eleven brain metastases were effectively treated using this system by concentrating the dose distribution at each of the metastases. The average dose in the normal brain was as small as 8 Gy.SRS in Japan began with the Gamma Knife tech-nology, but a few years later, LINAC-based SRS was started. The LINAC-based SRS was widely used, as IMRT, SRS, and conventional irradiation could be performed using the same LINAC system. In recent years, stereotactic irradiation has be selected even for multiple brain metastases if it possible. Although indications of SRS have expanded, methods of radiation therapy in future would need to be selected according to individual patient back-grounds.The author gratefully acknowledge to all Radiation Oncology staffs in Juntendo University Hospitals. No funding was received.YN contributed to the conception, drafting the manuscript, and preparation of figures and tables.The Author declares that there are no conflicts of interest.463ConclusionAcknowledgmentsFundingAuthor contributionsConflicts of interest statement