Effect of gamma knife dose rate and tumor-specific factors on treatment outcomes in brain metastases: insights from a cohort study.

Abstract

Purpose: This study aims to investigate the influence of Gamma Knife dose rate on treatment outcomes, in conjunction with tumor-specific factors of composition, size, and primary tumor location.

Methods: This retrospective cohort study analyzed 173 patients with 451 brain metastases treated between 2011 and 2015. Radiosurgery was performed using the Leksell Gamma Knife System, with dose rates categorized into four groups based on cobalt-60 decay: 2.9-2.7, 2.7-2.5, 2.5-2.3, and 2.3-2.1 Gy/min. Tumors were further classified according to dose rate into a simplified high/low classification (cutoff: 2.5 Gy/min) for clinical applicability. The Response Assessment in Neuro-Oncology Brain Metastases Group (RANO-BM) criteria were employed to evaluate treatment response. Statistical analyses were conducted to assess associations between dose rate, tumor characteristics, and outcomes.

Results: No significant association was identified between dose rates and treatment response (p = 0.35), indicating effective tumor control even at lower dose rates. Tumor composition and size had a significant impact on outcomes; cystic tumors demonstrated poorer responses compared to solid tumors, and larger tumors exhibited reduced efficacy. Specific primary tumor sites, particularly renal cell carcinoma and malignant melanoma, were linked to less favorable responses, confirming their radioresistant characteristics.

Conclusion: This study highlights that dose rate does not significantly impact treatment outcomes in Gamma Knife radiosurgery for brain metastases, indicating that effective tumor control can be achieved even at lower dose rates. These findings provide reassurance regarding the efficacy of treatments utilizing decaying cobalt-60 sources and highlight the importance of patient- and tumor-specific factors in predicting radiosurgical outcomes.