In addition to the brain MRI, ask for a full spine MRI, ie, thoracic, cervical, and lumbar. I wish we would've had all these MRI s done when my husband had unbalance issues after receiving the same treatment. Could've been the beginning of leptolemengeal metastasis, which would've gotten him treatment earlier for that. Leptolemengeal metastasis is rare but common in lung and breast Cancer and is often overlooked until it's harder to treat.