Radiation Therapy for Colorectal Cancer
Radiation therapy (radiotherapy) is a treatment option for colorectal cancer that uses high-energy x-rays to kill tumour cells. The rays enter the body and disrupt the DNA (genetic material) within the cells, which limits their ability to divide and replicate. Though radiation affects both normal and tumour cells, it is more damaging to cancer cells which divide more rapidly.
When is Radiation Therapy Used?
Radiation therapy is used primarily to treat stage II, III and IV rectal cancer before and after surgery. Often radiation on its own or in combination with chemotherapy (chemoradiation) is used to shrink large tumours before surgery, making it easier to completely remove the tumour.
For the treatment of colon cancer, radiation therapy is limited to palliative (non-curative) therapy to relieve symptoms associated with selected metastatic sites such as bone or brain metastases.
When is Radiation Therapy Used?
Radiation therapy is used primarily to treat stage II, III and IV rectal cancer before and after surgery. Often radiation on its own or in combination with chemotherapy (chemoradiation) is used to shrink large tumours before surgery, making it easier to completely remove the tumour.
For the treatment of colon cancer, radiation therapy is limited to palliative (non-curative) therapy to relieve symptoms associated with selected metastatic sites such as bone or brain metastases.
Before Surgery
Radiation given before surgery (neoadjuvant radiotherapy) shrinks the tumour to make it easier to remove and reduces the risk of the cancer coming back after surgery. You may be prescribed short course (such as five days) or long course (such as five treatments a week, for five or six weeks) radiation depending on the size of your tumour.
After Surgery
Radiation can also be given after surgery (adjuvant radiotherapy) to reduce the chances of the cancer returning. The course of radiation can vary from five to six weeks.
Palliative Radiotherapy
In advanced colorectal cancer (Stage IV), radiation may be given to help to alleviate or control symptoms, such as bone pain.
Types of Radiation Therapy
This is the most common type of radiation therapy. A machine outside the body sends a beam of radiation at the cancer cells and the immediate surrounding area to destroy the main tumour and any nearby cancer cells. A team of specialists will work together to determine the exact location at which to aim the radiation, controlling the size and shape of the beam to be as exact as possible in order to minimize damage to healthy cells.
The entire process can take a few hours but the treatment itself lasts a few minutes. This type of radiotherapy is used more frequently with rectal cancer compared to colon cancer, because the rectum does not move as much as the colon making it an easier organ to target. It is used in colon cancer mainly for relief of symptoms associated with advanced cancer. It may also be used to target metastatic tumours that compress other organs causing pain.
This type of radiation involves the implantation of radioactive sources inside or near the tumour. This type of radiation can deliver a high dose of radiation directly to the cancer while limiting the damage to surrounding healthy tissues and organs. This method is sometimes used in treating people with rectal cancer, particularly those who are unable to undergo surgery. Further research is necessary to know how to use brachytherapy most effectively.
To learn more about other radiation therapies, see Colorectal Cancer & You.
Types of Radiation Therapy
Side Effects of Radiation Therapy
While chemotherapy affects your whole body, radiation therapy only affects the specific area of the body where it is applied. Newer technology has allowed radiation therapy to be more precise, affecting only the target tissues as much as possible. If you are going to receive radiation therapy, talk to your doctor to learn what to expect and what measures can be taken to reduce any discomfort.
Possible Short-term Side Effects of Radiation Therapy:
Be sure to talk to your nurse or doctor right away if you notice any side effects so that steps can be taken to reduce and relieve them. Most side effects should go away gradually after treatment ends. If you receive radiation and chemotherapy together, you may experience more side effects.
Possible Long-term Side Effects of Radiation Therapy:
Long-term changes to the way your intestine works, such as diarrhea, being woken from sleep to have a bowel movement, have less control over your bowel movements (less warning to get to the toilet in time, or having accidents)
Damage to the bones in your pelvis, leading to a higher risk for fractures (be sure to discuss any pain or stiffness in your pelvis or back with your medical team)
Damage to sperm and eggs, causing possible infertility. Contraception should still be used during treatment and about a year afterward in case there is any chance of pregnancy. It may be possible to preserve sperm or eggs in advance of your treatment to preserve fertility. Speak to your medical team before you begin treatment to learn more.
