Our research group has come up with an equation that could be used to predict each patient's MTD using baseline clinical and laboratory measures before starting hydroxyurea treatment. The purpose of this research study is to compare the use of our equation for predicting MTD to the current standard practice of gradually increasing the hydroxyurea dose until MTD is reached. We want to see if the use of our predictive equation will allow us to achieve MTD faster and with no more side effects than with the standard practice.