Patients who have limited stage small cell lung cancer are presently treated with chemotherapy and radiation therapy (RT). Despite this aggressive treatment the vast majority of patients will have their cancer recur after treatment. A recurrence is not curable at this time, therefore efforts to reduce recurrence rates are desirable. Due to the sensitivity of surrounding structures in the chest to radiation, it has not been possible to give doses that can cure most tumours. Three-dimensional conformal radiotherapy is a special form of radiation therapy that allows doctors to reduce the amount of radiation dose to normal tissues and therefore reduce toxicity and in turn, let them safely increase the dose to tumours. The purpose of this study is to determine whether the combination of three-dimensional conformal radiotherapy and chemotherapy will be a more effective treatment. If the treatment is found to be safe for the first group of patients, then the total radiation dose will be increased for the next group of patients who are treated on this study.