Determine if stereotactic radiosurgery (Gamma Knife/CyberKnife) is appropriate for the current metastatic burden.
Guidelines & Evidence
Clinical Details
Section 1
When to Use
When to Use
Determining if a patient with newly diagnosed brain metastases can avoid Whole Brain Radiation Therapy (WBRT) in favor of Stereotactic Radiosurgery (SRS).
Justifying surgical resection instead of SRS for massive tumors.
Section 2
Literature
Development
Determined through several landmark RTOG parameters. While WBRT historically arrested metastatic growth, it uniformly caused devastating cognitive decline (dementia) after 6-12 months. SRS (Gamma Knife/CyberKnife) was developed to fry the tumors with sub-millimeter precision while saving the hippocampus and normal cortex. However, physics limits SRS: blasting a tumor >3cm with a single high-dose fraction will cause the brain around it to undergo fatal radiation necrosis.
Section 3
Pearls/Pitfalls
The Evolving Number Limit
Historically, guidelines hard-capped SRS at 3 or 4 metastases. Modern Yamamoto data (Lancet Oncol, 2014) proved that patients with 5-10 metastases treated with SRS have identical survival to those with 2-4 mets, provided the TOTAL combined volume is low (usually < 15cc). The limit is shifting from pure lesion count to cumulative volume.
Section 4
Evidence Appraisal
Primary Reference
Stereotactic radiosurgery for patients with multiple brain metastases (JLGK0901): a multi-institutional prospective observational study
Yamamoto M et al. • Lancet Oncol. 2014;15(4):387-95
