NgFUS NIVO: NeuroNavigation-Guided Focused Ultrasound With Nivolumab in Relapsed and Progressive DMG and Other High Grade Brain Tumors

Inclusion Criteria: * Age ≥ 3 and ≤ 25 years. * Diagnosis of brainstem DMG/DIPG or any high-grade brain tumor. * Group A: Relapsed or progressive brainstem DMG. * Group B: Relapsed or progressive high-grade intracranial brain tumor requiring surgical resection. * Lansky/Karnofsky rating ≥ 60. * Patients must have received at least one line of prior therapy upfront for their disease. * At least four weeks from radiation therapy, prior immunotherapy, or monoclonal antibody therapy. * At least 2 weeks from prior myelosuppressive chemotherapy and post nadir meeting organ function criteria. * At least 1 week or 5 half-lives (whichever is longer) from last targeted therapy. * If on steroids, stable or decreasing dose for at least 7 days prior to study entry and ≤ 0.4 mg/m2/day of dexamethasone or equivalent. * Stable or improving neurological status for 7 days prior to study entry. * Organ function: * Absolute Neutrophil Count (ANC) ≥750/μL. * Absolute Lymphocyte Count (ALC) \>500/μL. * Platelets ≥75K, unsupported. * Coagulation studies: PT and PTT \<1.5 ULN and INR (\<1.5). * Bilirubin ≤1.5x upper limit of normal (ULN). * AST/ALT ≤5x ULN. * Serum creatinine within normal limits for age. * Pulse oximetry \>93% on room air. * Ejection Fraction (EF) above institutional lower limit of normal (LLN). * For females of childbearing potential (FOCBP): negative pregnancy test within 7 days of study entry. * Patients of childbearing or child-fathering potential must …