 Approximately 200 to 250 patients are diagnosed with cancer each year at Childrens Medical Center Dallas, and based on prior institutional experience, two-thirds will have catheters inserted to facilitate chemotherapy. However, one-quarter of these patients have brain tumors and are not eligible due to the potential increased risk of intracranial hemorrhage with anticoagulation. There will be 100 patients each year who are at risk for CVC-related DVT. Based on previous studies, up to 50 of patients should develop occult DVT; however, only 35 of patients will likely be screened with radiographic imaging. Approximately 17 patients a year enrolled in the diagnosis study may be diagnosed with DVT and eligible for randomization. Therefore, total enrollment will be completed in approximately 3 years with an additional 4 months necessary to complete the follow-up period. 