<qa>  What is the purpose of this study?Drug exposure, not dose, determines treatment efficacy and neuropathy development. When treated with standard doses there is substantial variability in drug exposure meaning some patients are receiving less efficacious treatment than optimal. At this time we do not monitor a patients exposure because the optimal exposure level has not been defined. The purpose of this study is to prospectively enroll patients for systematic collection of exposure and neuropathy data in order to characterize this relationship. Once the relationship between cumulative exposure and neuropathy has been characterized, this model will be used to define an exposure target in future prospective exposure-guided dose-adjustment trials. 