 V. To assess the use of IUdR-DNA cellular incorporation measured by the investigational laboratory assays of flow cytometry and HPLC as an exploratory biomarker of IPdR for the following effects: the IUdR-DNA tumor cell incorporation from day 8 tumor biopsies in gastrointestinal GI cancer patients receiving MTD doses of IPdR as an exploratory biomarker of tumor radiosensitization using Response Evaluation Criteria in Solid Tumors RECIST criteria. 