Discovery of increased number or interval growth of brain metastases on same-day GammaKnife™ planning MRI: Predicting factors and patient outcomes.

Purpose: To determine factors associated with increased risk of finding new and/or enlarged brain metastases (BM) on GammaKnife™ (GK) MRI and their impact on patient outcomes.

Results: 43.9% of patients showed BM growth, 32.9% had additional brain metastases (aBM), and 18.1 % had both. Initial brain metastasis velocity (iBMV) was associated with finding aBM. Time between diagnostic MRI (dMRI) and GK MRI was associated with interval growth and each day increased this risk by 2%. Prior brain metastasectomy and greater time between either dMRI or latest extracranial RT and GK MRI predicted both aBM and BM growth. aBM and/or BM growth led to management change in 1.8% of cases and were not associated with OS or incidence of distant intracranial failure.

Conclusions: Number of metastases seen on dMRI and iBMV predicted both aBM and/or BM growth, however, these factors did not significantly affect survival or incidence of distant intracranial failure.