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 Criteria

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 Leksell Gamma Knife Icon system, both single-irradiation SRS and fractionated irradiation (stereotactic radiotherapy) have become possible using a mask fixation system. The purpose of this study was to evaluate the authors’ own institutional experience in order to re-examine 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 system at Rakusai Shimizu Hospital (September 2017 to February 2024). A retrospective study was conducted on 1043 patients who had undergone initial treatment with Gamma Knife Icon and had at least one posttreatment follow-up report. A comparison was made between cases that did (group A) and did not (group B, extended indication) meet the JLGK0901 criteria. Propensity score matching (PSM) was used to establish matched cases. Neurological death was the primary endpoint. Functional outcomes, imaging changes, and overall survival were secondary endpoints. RESULTS Of 1043 cases with newly diagnosed brain metastases treated with Gamma Knife Icon radiotherapy (GKRT) at Rakusai Shimizu Hospital, 673 (64.5%) were in group A and 370 (35.5%) in group B. PSM selected 321 cases in each group. The median survival time after GKRT 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), new distant intracranial lesions (imaging changes) (p = 0.925), neurological deterioration (p = 0.738), and severe radiation-induced adverse events (functional outcomes) (p = 0.994). Subgroup analysis of patients in group B with more than the allowed number of metastases or a greater tumor volume than that allowed in the JLGK0901 study showed no significant differences in neurological death and functional outcomes compared to group A for both subgroups. CONCLUSIONS The results support expansion of the indication for Leksell Gamma Knife Icon for METs from that in JLGK0901 based on the absence of the influence of the number of metastases and tumor volume on outcomes.