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Radiation therapy of anal cancer

Well to moderately differentiated T1 tumors < 1 cm N0

Regional lymph nodes are not included in the radiation field as the risk for subclinical disease is small. A tumor with margin is treated with 2 Gy fractionations to 54 Gy.

Poorly differentiated T1 tumors, T1 > 1 cm, and T2 tumors without evidence of lymph node metastases

Recommended radiation dose is:

  • 54 Gy to primary tumors and lymph node metastases with margin 
  • 46 Gy to areas at risk for involvement

Advanced primary tumors (T3-T4, N0 and all N+)

Recommended radiation dose is:

  • 58 Gy to primary tumor and lymph node metastases with margin
  • 46 Gy to areas at risk for involvement 

Cranially, the radiation field should reach the promontory level (splitting point for the common iliac artery) for tumors which grow into the rectum and N+ tumors. For T1-2N0 tumors localized distally to the dentate line, the upper field limit should be equivalent to the lower part of the ileosacral joints. The inguinal glands should be irradiated if the tumor in the anal canal stretches caudal to the dentate line, which is often the case.

For Paget's disease, local radiation treatment may be a good alternative to surgery. These rare cases should be evaluated by an oncologist and a surgeon.

Side effects that may occur during treatment

Acute side effects, (0-3 months from the start of radiation therapy), primarily affect cells that divide rapidly.

In combined (concomitant) treatment for anal cancer, radiation therapy causes the most acute side effects. Chemotherapy is responsible for a mild to moderate bone marrow suppression and leukopenia occurs often.

The acute radiation injury to the pelvis particularly affects the mucosa of the small intestine, germinal cells and skin. Further, the mucosa of the colon/rectum, the urothelium in the urinary tract and the vagina may also be affected.

All patients develop radiation dermatitis with varying extent during radiation therapy. The area around the anus, external genitalia, rima dormitory and groins are most affected.The skin becomes red and sore, and erosions may occur.

Many patients experience radiation enteritis with diarrhea, frequent bowel movements, urge and abdominal pain.This depends on the amount of intestine (especially the small intestine) located in the pelvis and thereby included in the radiation field. The mucous membranes of the vagina become sore. Fatigue and loss of appetite are common.

Most acute side effects disappear within six weeks after treatment.

However, the germinal cells are very sensitive to radiation therapy. In women the damage is irreversible and leads to infertility, since the ovaries usually are included in the radiation field.

Men may also become sterile. The testes may be difficult to shield from the radiation field.

If appropriate, the patient is offered sperm banking before the radiation therapy. 

 

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