Radiation colitis is injury to the colon caused by radiation therapy. It is usually associated with treatment for prostate cancer or cervical cancer.^[1] Common symptoms are diarrhea, a feeling of being unable to empty the bowel,^[2] gastrointestinal bleeding, and abdominal pain.^[1]

If symptoms of radiation colitis onset within 60 days of exposure to radiation, it is referred to as acute; otherwise, it is classified as chronic. Acute radiation colitis may onset within a few hours of radiation exposure, and may clear up within two or three months after radiation ends. Between 5 and 15% of individuals who receive radiation to the pelvis may have chronic radiation colitis.^[1] Radiation therapy can also affect the bowel at the small intestine (radiation enteritis) or the rectum (radiation proctitis).^[2]

Tenesmus or diarrhea appear to be the most common symptoms in patients with radiation colitis. Patients may also exhibit perforation or obstruction.^[2]

Radiation colitis is typically brought on by radiation therapy administered to the pelvis for prostate, cervix, uterus, anus, rectum, or bladder cancers.^[3]

Radiation primarily harms rapidly dividing cells by causing DNA strand loss that results in irreversible DNA changes. Consequently, the G2/M phase of the cell cycle, when the DNA strands are arranged into well-defined chromatin pairs and prepared for division into two daughter cells, is when radiation damage is greatest.^[4] Colocytes, the cells that divide quickly that make up the epithelium lining the colon, undergo regeneration every five to six days. Its quick regeneration also makes it more vulnerable to radiation-related damage.^[5]

Genetic and cytokine interactions are necessary for the active process of programmed cell death known as apoptosis. Research on animals has demonstrated a significant increase in intestinal crypt apoptosis following low-dose radiation exposure.^[6]

Through its strong fibrogenic and proinflammatory effects, TGF-β also plays a significant role in the pathogenesis of chronic radiation colitis. TGF-β levels in irradiated tissues are significantly higher and stay elevated in smooth muscle cells, vascular endothelial cells, and fibrocytes for up to 26 weeks.^[7]

Radiation colitis is characterized histologically by stromal injury followed by progressive fibrosis that results in epithelial atrophy and persistent mucosal ischemia.^[3]