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Curative radiation treatment of cancer in the colon and rectum

Medical editor Marianne Grønlie Guren MD

Oslo University Hospital


Curative radiation treatment of colon cancer

Radiation treatment for colon cancer is rarely administered and therefore not further described in this procedure.

Curative radiation treatment of rectal cancer

Curative radiation treatment has been used for many years for locally advanced rectal cancer. Due to intermediary radiation sensitivity, radiation treatment alone has not been considered potential curative treatment

Previously, radiation treatment was administered postoperatively in patients at risk of recurrence. Several studies show better effect by giving radiation therapy before surgery, with less side effects. About 30-40% of patients with rectal cancer receive radiation treatment before surgery.

Radiation treatment is usually given in fractions of 2 Gy, totally 50 Gy. The treatment is given on 25 weekdays. 

The effect of radiation treatment is enhanced when combined with chemotherapy (5-FU regimens). Combining radiation therapy with oral capecitabine or FLV intravenously is most common. The effect on the tumor is better and there are few additional side effects (4).

For some patients it may be appropriate to provide radiation treatment over a shorter period, and in larger fractions. 5 Gy is given on 5 weekdays, totally 25 Gy.


Preoperative radiation

  • Preoperative radiation treatment, 2 Gy x 25, with chemotherapy is recommended in patients with T4 tumor or with tumor tissue with distance less than 3 mm from the mesorectum assessed by pelvic MRI. This treatment is also given to patients with lymph node metastases outside the mesorectal fascia.
  • 5 Gy x 5 may be appropriate in elderly patiens or patiens with comorbidity. This treatment is also increasingly used if metastases are found. One may then provide more chemotherapy and radiation therapy.
  • Local recurrence generally requires radiation therapy before surgery. Reradiation should be considered, if the patient previously has received radiation treatment. In some cases the treatment is given divided in two daily doses (hyperfractionated), to protect healthy tissue.

Postoperative radiation

Postoperative radiation can be given when preoperative radiation is not given in cases of:

  • T4 tumor
  • preopertively or peropertively perforation of the tumor or near the tumor 
  • microscopic or macroscopic remaining tumor


The radiation therapy is usually given to reduce the tumor and to enable radical surgery with wide margins. This is shown to be important in preventing local recurrence of the disease and may also contribute to improved survival.



Target Volume   



Definitions of target volume according to ICRU
(International Commission on Radiation Units and Measurements)
GTV (Gross Tumor Volume) Palpable or visible/identifiable area of malignant growth.

CTV (Clinical Target Volume)

Tissue volume containing GTV and/or subclinical microscopic malignant disease.

ITV (Internal Target Volume)

Volume containing CTV plus one inner margin taking into account inner movements and changes in CTV.

PTV (Planning Target Volume) Geometric volume containing ITV with set up margin taking into account patient movement, variation in patient positioning, and field modeling.



  • CT and MRI if needed for dosage planning.
  • The patient receives small tatoos or it is drawn with a marker directly on the patient's skin.
  • The location of the tumor and risk areas are drawn in on the CT- images and a 3-dimensional radiation volume is created.
  • The radiation field is approved by a medical physicist and physician. Ideally, a uniform dose distribution over the target volume is desired with no radiation to critical organs. In reality, this is impossible to achieve.
  • The patient should lie in the supine position during treatment and the bladder should be moderately filled.

The treatment plan is transferred to the radiation machine. At the first treatment, carefully setting of the radiation field is done (virtuell simulation). Then the treatment is given usually once daily on weekdays. Treatment usually starts one week after CT for dosage planning is taken.


The radiation field includes mainly the posterior part of the pelvis. If there is extensive tumor growth or affection of the vagina, prostate, bladder, or if there is suspicion of lymph node affection in the anterior part of the pelvis, a larger radiation field is given, including large parts of the pelvis and in some cases the groins.

Radiation treatment is usually given in 2 Gy fractions daily. Toward the pelvis, 46 Gy is given where fatty tissue with mesorectum on the pelvic wall is included in the radiation field. Often, a boost is given to the tumor itself of 2 Gy x 2. The normal tissue better tolerates the radiation when this is given as small fractions and with intervals.


The patient is reassessed after 4-6 weeks and is usually operated 6-8 weeks after completed radiation treatment. During this time a reduction of tumor volume will occur while some of the acute radiation side effects will decrease.

Side effects

Outpatient treatment is common. If the journey is long, a patient hotel may be appropriate. Some patients, especially elderly, may require hospitalization during parts of the treatment due to side effects.  Side effects are divided into acute and chronic.


With the present radiation technique a pause in the treatment is seldom required. However, more potent radiation sensibilizing chemotherapy increases the chance of problematic side effects. Acute side effects often occur 2-4 weeks after starting radiation treatment and vary greatly in extent and character (20).

  • Fatigue is experienced by many
  • Nausea occurs frequently
  • Skin soreness, especially around the anus. This is common in lower rectal cancer.
  • Diarrhea occurs and is caused by both irritation of the rectum/small intestine and the effect of the radiation field on the small intestine.
  • Initially in the treatment, constipation/ileus can occur when a tight bowel lumen becomes even tighter due to tumor and increasing bowel edema.
  • Urinary tract problems with frequent and painful urination occur, and are caused by irritation of the bladder wall and not necessarily infection. 


Delayed side effects are often caused by destruction of the normal tissue with development of fibrosis and therefore reduced function.

  • Younger women radiated to the pelvis start menopause and have dry mucous membranes in the vagina (20).
  • Men may become infertile and experience erectil dysfunction (20).
  • Abdominal pain, diarrhea, and constipation depend to a varying degree on fibrosis in the small intestine and colon and may possibly lead to  ileus. 
  • Altered bowel function is common in the form if frequent and loose stools. Radiation treatment to the anal canal may lead to fecal incontinence, to varying degrees (20).
  • The bladder may have reduced volume and poor sphincter function with subsequent pollakisuria and incontinence.
  • Radiation to the pelvic bone may cause fractures which are often minor and difficult to diagnose.

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