Validity of a Recently Proposed Prognostic Grading Index, Brain Metastasis Velocity, for Patients With Brain Metastasis Undergoing Multiple Radiosurgical Procedures

Purpose: This study of our patients with brain metastasis who underwent multiple stereotactic radiosurgery (SRS) procedures aimed to validate whether the recently proposed prognostic grading system, brain metastasis velocity (BMV), is generally applicable. The BMV scores the cumulative number of new brain metastases that developed after the first SRS divided by time (years) since the initial SRS. Patients were categorized into 3 classes by their BMV scores (ie, ≤3, 4-13, and ≥14). Methods and Materials: This retrospective cohort study was approved by the Tokyo Women's Medical University Institutional Review Board (number 1981). We used our prospectively accumulated database, which included 833 patients who underwent a second SRS procedure for newly detected lesions, using a gamma knife, for brain metastases. Patients who had whole-brain radiation therapy were excluded. The procedures took place during the 19-year period between July 1998 and June 2017. Furthermore, among the 833 patients, 250 underwent a third SRS procedure, and 88 had a fourth SRS procedure. Results: The median survival times (MSTs) after the second SRS were 12.9 months (95% confidence interval [CI], 10.2-17.1) for the BMV group with a score of ≤3; 7.5 months (CI, 6.5-9.0) for the group scoring 4 to 13, and 5.1 months (CI, 4.0-5.6) for the group scoring ≥14 (P =.0001). The corresponding MSTs after the third SRS were 13.2 months (95% CI, 9.1-21.6), 8.0 months (CI, 6.2-11.2), and 5.7 months (CI, 4.8-7.8; P =.0001). Respective MSTs after the fourth SRS were 13.2 months (95% CI, 9.1-21.6), 8.0 months (CI, 6.2-11.2), and 5.7 months (CI, 4.8-7.8; P <.0001). The mean BMV score of patients with small cell lung cancer, 24.8, was significantly higher than that of patients with non-small cell lung cancer, 17.7 (P =.032). Conclusions: Our present results support the validity of BMV for predicting survival not only after the second SRS but also after the third and fourth SRS.