P11.11.B EVALUATION OF THE PROGNOSTIC SIGNIFICANCE OF BRAIN METASTASIS VELOCITY IN PATIENTS UNDERGOING INTRACRANIAL STEREOTACTIC RADIOTHERAPY

Abstract BACKGROUND Despite the availability of targeted therapies, brain metastasis (BM) continue to pose a significant challenge, especially in the context of solid organ tumors, with lung cancer being the most affected. Stereotactic radiotherapy (SRT) plays a crucial role in the treatment of BM by providing effective local control while minimizing damage to healthy brain tissue. Brain metastasis velocity (BMV) has been suggested as a prognostic factor for overall survival (OS) in patients with BM. This study aims to explore the prognostic significance of the validated initial brain metastasis velocity (iBMV) in patients undergoing SRT for BM. MATERIAL AND METHODS Patients diagnosed with BM who received intracranial SRT at our clinic between 2021 and 2024 were included in this study. The iBMV was calculated by dividing the number of BM present at the time of the first brain event by the total time elapsed from the initial cancer diagnosis to the occurrence of the first BM. To analyze the prognostic and predictive role of iBMV on OS, we conducted log-rank tests as well as linear, logistic, and Cox regression analyses. RESULTS A total of 40 patients with 76 BM lesions were included in the study. The median age of the patients was 67 years (range: 42-76), with 5 patients (12.5%) female and 35 (87.5%) male. The majority of the patients (37; 92.5%) had primary lung cancer, while 3 patients (7.5%) had primary tumors that were not lung cancer. The median time from the initial diagnosis to the occurrence of brain metastases was 5.5 months (range: 0-112). Notably, 8 patients (20%) presented with BM at the time of their initial diagnosis. The median number of metastases treated with SRT was 1.5 (range: 1-5). Half of the patients (20; 50%) received SRT for a single BM, while the other half underwent SRT for multiple metastases. The median iBMV was 2.58 (range: 0.11-50.00). After a median follow-up period of 11.5 months (range: 1-38) 14 patients (35%) died, while 26 patients (65%) were still alive with disease. When the patients were categorized based on iBMV into low-risk (iBMV <2) and high-risk (iBMV ≥2) groups, it was found that the median OS was significantly lower in the high-risk group (p=0.001). CONCLUSION Our study shows that the initial brain metastasis velocity is a straightforward, practical, and reliable prognostic parameter for predicting overall survival in a recently treated and homogeneous cohort of patients with brain metastases at various time points. However, it is important to compare and validate different definitions of brain metastasis velocity. Evaluating iBMV values in a larger patient cohort will not only help assess treatment outcomes but also provide insights into subsequent metastatic events throughout the disease course. This information will assist in making informed decisions regarding the need for re-irradiation, fractionation strategies, and treatment expectations for patients undergoing SRT.