For low risk cancers the results are similar to those of surgery. However, the relapse rate appears to be higher if the cancer becomes more extensive or more aggressive.
Traditionally, radiotherapy has been delivered over six or seven weeks. The advantage of radiotherapy is that it can be performed on unfit patients and patients who wish to avoid surgery. The disadvantage is the difficulty of salvage surgery if it fails. On the other hand, radiotherapy may safely follow surgery.
Short term side effects include radiation sickness and cystitis, all of which usually resolve within three to six months. In many patients, rectal compliance decreases, leading to frequent bowel actions.