Low Dose Preoperative Radiation in the Treatment of Carcinoma of the Rectum

Abstract

Recent advances in the treatment of cancer of the rectum show a steady improvement in survival. Newer surgical techniques and expanding options for adjunctive therapy appear to have had a significant impact on improving both local control and distant disease. Five-year survival of patients now ranges from 85-90% for stage I cancers and 50-55% for stage III cancers. Local recurrence of disease following curative surgical resections is dependent on the stage of the tumor and for some high-risk patients, stages T3/T4 and N+ disease, has been reported as high as 40-60%. In an attempt to lower the rate of local recurrence and improve survival, several approaches to adjuvant therapy have been utilized. Preoperative radiation was one approach that has been used extensively in the last decades. Recently, the large Swedish randomized studies using a short course (5 Gy x 5) of preoperative radiation have reported a clear improvement in local control and survival of patients. These results were achieved with no downstaging of disease since surgery was perfomed put immediately after irradiation. Therefore it should be presumed that preoperative radiation therapy resulted in the sterilization of tumor cells, which prevented both local and distant dissemination leading to the improved outcome. The question remains, therefore, as to what is the least and/or the most appropriate dose of preoperative irradiation that can achieve the beneficial effect of minimizing tumor cell dissemination at surgery. Low dose preoperative irradiation as a single fraction of 500 cGy appears to have a sound biological basis and in single institutional studies it was shown to be effective but in randomized studies it did not improve results. This is likely to be due to a poor design of trials and/or inapproppriate patient selection for these studies. A well-designed study still remains to be done.