10099- MET-10 A PROPENSITY SCORE-MATCHED ANALYSIS OF STEREOTACTIC RADIOTHERAPY FOR METASTATIC BRAIN TUMORS USING THE LEKSELL GAMMA KNIFE ICON MASK SYSTEM: A SINGLE-CENTER RETROSPECTIVE COMPARATIVE STUDY OF CASES MEETING AND NOT MEETING THE JLGK0901 C

Abstract OBJECTIVE Stereotactic radiosurgery (SRS) for metastatic brain tumors (METs) has previously been considered to be indicated only for cases with a few lesions with small sizes. Expansion of the indication of SRS for METs is mainly due to the JLGK0901 study. Furthermore, since introduction of the Leksell Gamma knife Icon, both single irradiation and fractionated irradiation has become possible using a mask fixation system. The purpose of this study was to evaluate our own institutional experience in order to reexamine the limitations on the number and volume of lesions established in the JLGK0901 study. METHODS The study period was 6.5 years from the start of operations using the Leksell Gamma Knife Icon at Rakusai Shimizu Hospital (2017/09-2024/02). A retrospective study was conducted in 1043 patients who had undergone initial treatment with Gamma Knife Icon and had at least one post-treatment follow-up report. A comparison was made between cases that did (Group A) and did not (Group B, extended indication) meet JLGK0901 criteria. Propensity score matching was used to establish matched cases. Neurological death was the primary endpoint. Functional outcomes and imaging changes were secondary endpoints. RESULTS Of 1043 cases, 673 were in Group A and 370 were in Group B. The median survival time after Gamma Knife Icon radiotherapy was shorter in Group B (19.7 vs. 10.6 months, p<0.01), but the incidence of neurological death did not differ significantly between the two groups (p=0.635). There were also no significant differences in the rates of poor local control (p=0.381) and new intracranial lesions (p=0.925), or in neurological deterioration (p=0.738) and severe radiation-induced adverse events (p=0.994). CONCLUSIONS The results support expansion of the indication for Leksell Gamma Knife Icon for METs from that in JLGK0901 based on the absence of an influence of the number of metastases and tumor volume on outcomes.