LINAC-based single-isocenter stereotactic radiotherapy for multiple brain metastases

Advances in chemotherapy and radiotherapy have expanded indications for stereotactic radiosurgery/radiotherapy (SRS/SRT) for multiple brain metastases. We introduced the Elements Multiple Brain Mets System (mSRS/SRT system), using the dynamic conformal arc method with a single isocenter, for treatment of multiple brain metastases with SRS/SRT (mSRS/SRT). This study analyzed outcomes of mSRS/SRT. From December 2018 to March 2023, 29 patients (130 lesions) were treated using the mSRS/SRT system. The prescribed dose for the planning target volume, determined by D95%, was 21 or 18 Gy in a single fraction for a tumor diameter ≤2 cm and 27 Gy in 3 fractions or 35 Gy in 5 fractions for a tumor diameter >2 cm. Median follow-up time was 7.2 months. The 12-month overall survival rate was 48.5%, and systemic therapy after mSRS/SRT was associated with better overall survival. The 12-month lesion-based local recurrence rate was 14.4%, and larger tumor diameter was associated with poorer local control, whereas systemic therapy after mSRS/SRT was associated with better local control. The 12-month intracranial control rate was 43.6%, and non-lung primary tumors, a greater number of lesions, and systemic therapy before mSRS/SRT were associated with poorer intracranial control. Acute adverse events included 4 cases of Grade 1 headache, one of Grade 1 nausea, and one of Grade 2 alopecia. Brain necrosis was observed in 9 patients (13 lesions), and all cases were asymptomatic. These results suggest that the mSRS/SRT system may become a treatment option for multiple brain metastases, although further evaluation is needed.