DISEASE CHARACTERISTICS:

   - Histologically or cytologically confirmed diagnosis of a solid tumor malignancy within
   the past 5 years

      - If the original histologic proof of malignancy is > 5 years, then pathological
      (i.e., more recent) confirmation is required (e.g., from a systemic metastasis or
      brain metastasis)

   - Brain metastases must be visible on contrast-enhanced MRI or a contrast enhanced CT
   scan (for patients unable to undergo MRI within the past 28 days)

      - Patients unable to undergo MRI imaging because of non-compatible devices are
      eligible, provided the contrast-enhanced CT scans are obtained and are of
      sufficient quality

      - Patients who had undergone radiosurgery or surgical resection and are planning
      adjuvant whole-brain radiotherapy do not have to have visible disease but do need
      a baseline MRI

   - Must have stable systemic disease (i.e. no evidence of systemic disease progression
   within the past 3 months)

   - Patients with brain metastases at initial presentation are eligible and do not need to
   demonstrate 3 months of stable scans

PATIENT CHARACTERISTICS:

Inclusion

   - Karnofsky performance status 70-100%

   - Serum creatinine ≤ 3 mg/dL and creatinine clearance ≥ 30 mL/min

   - Total bilirubin ≤ 2.5 mg/dL

   - Blood urea nitrogen (BUN) < 20 mg/dL

   - Mini-mental status exam score ≥ 18

   - Negative serum pregnancy test

   - Fertile patients must practice adequate contraception

Exclusion

   - Severe, active co-morbidity, defined as follows:

      - Unstable angina and/or congestive heart failure requiring hospitalization within
      the last 6 months

      - Transmural myocardial infarction within the last 6 months

      - Acute bacterial or fungal infection requiring intravenous antibiotics at the time
      of registration

      - Chronic obstructive pulmonary disease exacerbation or other respiratory illness
      requiring hospitalization or precluding study therapy at the time of registration

      - Hepatic insufficiency resulting in clinical jaundice and/or coagulation defects

   - Pregnant or lactating women

   - Prior allergic reaction to memantine hydrochloride

   - Current alcohol or drug abuse

   - Intractable seizures while on adequate anticonvulsant therapy (i.e., more than one
   seizure per month for the past 2 months)

PRIOR CONCURRENT THERAPY:

Inclusion

   - At least 14 days but no more than 56 days since prior therapy for brain metastasis,
   including radiosurgery and surgical resection

   - No systemic chemotherapy for 14 days prior, during, or for 14 days after completion of
   whole-brain radiotherapy (WBRT)

Exclusion

   - Prior cranial radiotherapy

      - Patients may have received up to 3 prior WBRT treatments and still be registered
      and randomized on the protocol provided WBRT parameters meet protocol
      requirements

   - Chronic short-acting benzodiazepine use