Gamma knife surgery for 1–10 brain metastases without prophylactic whole-brain radiation therapy: analysis of cases meeting the Japanese prospective multi-institute study (JLGK0901) inclusion criteria

We evaluated the results of stereotactic radiosurgery (SRS) alone using gamma knife (GK) for selected patients with 1–10 brain metastases without prophylactic whole-brain radiation therapy (WBRT) among JLGK0901-eligible cases. Seven hundred seventy-eight consecutive cases meeting the following JLGK0901 study inclusion criteria were analyzed: (1) newly diagnosed brain metastases, (2) 1–10 brain lesions, (3) less than 10 cm³ volume of the largest tumor, (4) less than 15 cm³ total tumor volume, (5) no magnetic resonance (MR) findings of cerebrospinal fluid (CSF) dissemination, and (6) no impaired activity of daily living [<70 Karnofsky Performance Score (KPS)] due to extracranial disease. At initial treatment, all lesions were irradiated with SRS without upfront WBRT. Thereafter, enhanced magnetic resonance imaging (MRI) was applied every 2–3 months, and new distant lesions were appropriately retreated with SRS or WBRT. We divided patients according to tumor number: single lesion for group A (280 cases), 2 for group B (135), 3–4 for group C (148), 5–6 for group D (93), and 7–10 for group E (122). Differences among groups were compared in terms of overall, neurological, qualitative, and new-lesion-free survival (NLFS). Median age was 65 years (range 26–92 years). There were 505 men and 273 women. The primary organ was lung in 579 patients, gastrointestinal tract in 79, breast in 48, urinary tract in 34, and others/unknown in 38. Mean survival time was 0.72 years (0.83 years for 1, 0.69 years for 2, 0.69 years for 3–4, 0.59 years for 5–6, and 0.62 years for 7–10 metastases). On multivariate analysis, significant poor prognostic factors for overall survival (OS) were active systemic disease, poor (<70) initial KPS, and male gender. Neurological survival and qualitative survival at 1 year were 92.7% and 88.2%, respectively. NLFS at 6 months and 1 year were 69.8% and 43.8%, respectively. There were statistically significant differences in new lesion emergence between groups A and B and between groups B and C. SRS using GK provides excellent results in selected patients with 1–10 brain lesions, without prophylactic WBRT. This study revealed that brain lesion number has no effect on any of the four types of survivals, which is anticipated to be confirmed by the JLGK0901 study.