What is the purpose of preoperative radiotherapy for rectal cancer

The purpose of preoperative radiotherapy for rectal cancer is to: 1. shrink the tumor, reduce the stage and thus increase the surgical resection rate; 2. increase the chance of preserving the anal sphincter for low-lying rectal cancer; 3. reduce intraoperative implantation and local tumor recurrence.

Pathological studies of surgical specimens after radiotherapy have shown that preoperative radiotherapy can reduce the size of the tumor to varying degrees, and the degeneration of tumor cells, proliferation of fibrous tissue, and disappearance of peritumoral infiltration. Tumor cells undergo necrosis and fibrosis after radiotherapy, which can reduce the chance of tumor cells falling off due to traction and squeezing during surgery, and reduce the proliferation activity of tumor cells, tumor implantation and survival. The advantage of preoperative radiotherapy is that tumor cells are relatively oxygen-rich and more sensitive to radiation than after surgery; the small intestine is not affected by surgery, and the toxicity of the treatment is also relatively small.

The disadvantage of preoperative radiotherapy is that due to the limitations of current imaging diagnostic technology, the accuracy of preoperative staging cannot be fully guaranteed, which may lead to overtreatment of early-stage patients or cause some patients who are not found in preoperative examinations to receive unnecessary radiotherapy.

The main systemic reactions to rectal cancer radiotherapy include fatigue, nausea, vomiting, and leukocytopenia, which are generally not serious and only require symptomatic treatment. A few patients with severe reactions need to suspend radiotherapy and receive fluid support.

The dose-limiting organs that affect radiotherapy for rectal cancer are mainly the small intestine and bladder. Not only should we pay attention to the acute damage during irradiation, but we should also consider the long-term reactions after radiation. The average irradiation dose of the small intestine is generally limited to 45-50Gy, and the bladder limit dose is V60≤50%, that is, the bladder volume receiving 60Gy and above is limited to 50%. Especially for the small intestinal tissue, due to the rapid proliferation of mucosal basal cells and sensitivity to radiation, the villi of the small intestine can be completely shed during high-dose irradiation. The acute reactions to radiotherapy for rectal cancer are manifested as diarrhea and indigestion, which are generally tolerated after symptomatic treatment. Excessive irradiation doses can cause mucosal ulcers, perforations, and even fistulas. Long-term reactions can cause small intestinal stenosis and obstructive symptoms, which should be paid special attention to. Bladder radiation reactions can be manifested as urinary tract irritation symptoms such as frequent urination and urgency, and late reactions are mainly bladder contracture and dysfunction.