Ph I Study of Lithium During Whole Brain Radiotherapy For Patients With Brain Metastases

Inclusion Criteria: * Histopathologically confirmed extracranial primary malignancy * Multiple (i.e., \> 3) brain metastases OR \< 3 metastases with at least 1 metastasis \> 4.0 cm in diameter * Not eligible for radiosurgery * No requirement for immediate whole-brain radiotherapy * No metastases to the midbrain or brainstem Exclusion Criteria: * Zubrod performance status 0-2 * Life expectancy ≥ 8 weeks * Platelet count \> 100,000/mm\^3 * ANC \> 1,500/mm\^3 * Hemoglobin ≥ 10 g/dL * BUN \< 25 mg/dL * Creatinine \< 1.5 mg/dL * Bilirubin \< 1.5 mg/dL * ALT ≤ 2 times normal * Sodium \> 136 mg/dL * Not pregnant or nursing * Negative pregnancy test * Fertile patients must use effective contraception * Neurologically stable * No seizure disorders or seizures due to brain metastases * No medical illnesses or psychiatric conditions that would preclude completion of study treatment * No sensory neuropathy ≥ grade 2 * No bipolar disorder * No thyroid disease * No QTc interval prolongation PRIOR CONCURRENT THERAPY: * More than 2 weeks since prior and no concurrent chemotherapy * At least 2 weeks since prior and no concurrent NSAIDs, angiotensin-converting enzyme inhibitors (e.g., enalapril or captopril), calcium channel blockers, diuretics, selective cyclooxygenase-2 inhibitors, acetazolamide, urea, xanthine, or alkalinizing agents (e.g., sodium bicarbonate) * No prior radiotherapy to the head and neck area * No prior radiosurgery * No concurrent radiotherapy to other sites * No concurrent anticonvulsants due to brain metastases * No concurrent psychoactive drugs * No concurrent thyroid medications * No concurrent amifostine