Radiation therapy is a common treatment for rectal cancer, often used to improve the chances of a successful outcome. This treatment involves directing high-energy beams, typically external beam radiation, at the tumor and surrounding tissues to destroy cancer cells and shrink the mass before surgery. For many patients, radiation is delivered alongside chemotherapy, a combination known as chemoradiation, which enhances the cancer-fighting effect. This strategy, often used before surgery (neoadjuvant therapy), aims to reduce the risk of the cancer returning locally and may help preserve the rectal sphincter muscles. Although highly targeted, the radiation beams must pass through or near healthy organs in the pelvis, which can lead to a range of temporary or permanent side effects.
Acute (Immediate) Localized Effects
The immediate side effects of pelvic radiation are caused by the irritation of rapidly dividing cells lining the gastrointestinal and urinary tracts. These acute reactions usually begin one to two weeks into treatment, often worsen toward the end, and typically resolve within a few weeks or months after the final session. The most common gastrointestinal reaction is diarrhea, which results from radiation-induced injury to the intestinal lining, causing it to secrete more fluid and absorb less.
Patients frequently experience tenesmus, the distressing feeling of needing to pass a bowel movement even when the rectum is empty. This sensation is often accompanied by an urgent need to defecate and burning pain in the rectal area. The skin in the treatment field can also become red, tender, and irritated (radiation dermatitis), similar to a severe sunburn, particularly noticeable in skin folds due to moisture and friction.
The bladder, which sits close to the rectum, can develop radiation cystitis. This irritation causes increased frequency of urination and a strong, sudden urge to void. Some individuals report painful or burning sensations during urination, which is caused by the temporary inflammation of the bladder lining. These localized symptoms are generally considered temporary because the healthy cells of the bowel and bladder lining have a strong capacity to heal once the radiation exposure stops.
Chronic (Long-Term) Structural Changes
While acute side effects typically resolve, a distinct set of complications can persist or develop months to years after radiation therapy concludes. These chronic effects are fundamentally different, resulting from permanent tissue changes such as scarring, reduced blood flow, and fibrosis, where normal, elastic tissue is replaced by stiff, non-functional scar tissue. This process can significantly alter the structure and function of pelvic organs.
Chronic radiation proctitis is a persistent or recurring inflammation of the rectum that can cause long-term rectal bleeding, pain, and mucus discharge. Fibrosis can also lead to strictures, or narrowing in the bowel, which may obstruct the passage of stool and require medical intervention. Damage to small blood vessels in the pelvic area can also cause chronic pain and reduced flexibility in surrounding muscles and soft tissues.
Sexual Health Dysfunction
Sexual health dysfunction is a common chronic concern, affecting both men and women due to damage to nerves and blood vessels in the pelvis. Men may experience difficulty achieving or maintaining an erection (erectile dysfunction), and both sexes may experience a decreased libido. For women, radiation can cause vaginal tissues to become dry, less elastic, and narrow (stenosis), leading to painful intercourse or sometimes resulting in early menopause. Additionally, the bone tissue in the pelvis can weaken, increasing the risk of fractures years after treatment.
Strategies for Managing Side Effects
Active management of both acute and chronic side effects is a continuous process that requires close collaboration with the care team. For acute gastrointestinal symptoms, anti-diarrheal medications like loperamide are often prescribed to reduce the frequency of loose stools and allow the bowel to absorb more water. Dietary adjustments, such as temporarily following a low-fiber or low-residue diet, can also help by reducing the amount of undigested material that irritates the inflamed bowel. Patients should maintain high levels of hydration by drinking eight to ten glasses of fluid daily to replace the volume lost through diarrhea.
Systemic reactions like fatigue are common. Management involves balancing rest with light physical activity, such as short walks, which can help increase energy levels over time. For skin irritation, the treated area should be washed gently with mild soap and tepid water, then patted dry with a soft towel. The care team can recommend specific, non-irritating creams or ointments to soothe the skin and lock in moisture, while avoiding products that contain perfumes or alcohol.
Managing chronic symptoms often involves specialized care, such as physical therapy for pelvic pain or pharmacologic agents for sexual dysfunction. For chronic rectal bleeding from proctitis, treatments like steroid suppositories or argon plasma coagulation may be used to reduce inflammation and cauterize bleeding vessels. Patients should contact the medical team immediately if they experience a fever, severe abdominal pain, excessive bleeding, or diarrhea that is not controlled by prescribed medications. These signs can indicate a more serious complication, such as a bowel obstruction or infection, that requires immediate assessment.