Colorectal Cancer: Radiation Therapy
What is radiation therapy?
Radiation therapy uses high-energy beams of X-rays or other particles to kill cancer
cells or stop them from growing.
When might radiation therapy be used?
Radiation therapy is a common part of the treatment for rectal cancers. It’s also
may be used to treat colon cancer. But surgery is the main treatment for both colon
and rectal cancer.
Sometimes advanced colorectal cancer can’t be removed with surgery. And some people
are not healthy enough to have surgery. Then radiation can be very helpful. In this
case, it's often used along with chemotherapy.
Here are some reasons your healthcare provider may suggest radiation therapy:
To try to shrink a tumor before surgery. This may make it easier to take out the tumor. It might also reduce the amount of
To try to kill any cancer cells left after surgery. For colon cancer, it may be used if a cancer growth was attached to an organ or to
the lining of your belly (abdomen). In these cases, the surgeon may not be sure all
the cancer cells were removed. Radiation can kill any cancer cells that are left behind.
This helps reduce the chance that the cancer will come back.
To treat the exact area where the tumor was. Radiation can be used during surgery. After the tumor is removed, it can be aimed
right where the tumor was to kill any cancer cells left there. This is called intraoperative
radiation therapy (IORT).
To ease symptoms. Radiation can ease problems caused by tumors that can't be taken out or that have
spread to other organs. For instance, it can help shrink tumors that are causing blockages,
bleeding, or pain.
To treat other places where the cancer has spread. Radiation might be used to treat colorectal tumors that have spread to the brain
To plan your treatment, you will talk with a team of cancer specialists. This will
include a radiation oncologist, the doctor who creates your treatment plan. The plan
shows what kind of radiation you’ll have and how long the treatment will last. If
you need radiation along with chemotherapy, you’ll also see a doctor called a medical
What happens during radiation therapy?
For colorectal cancer, radiation most commonly comes from a large machine that sends
X-ray beams into the tumor. This is called external radiation. It's a lot like getting an X-ray, but more radiation is used.
In some cases of rectal cancer, a radioactive source is put right into or next to
the tumor. It gives off radiation for a short time over a short distance. This is
called internal radiation .
You may get external radiation therapy in a hospital or a clinic. You will likely
be an outpatient. This means you go home the same day. External radiation is often
given 5 days a week for many weeks. If you also need chemotherapy, you'll get it in
a different outpatient area.
Getting ready for radiation
Before your first treatment, you’ll have an appointment to plan for the treatment.
This is called simulation. During the simulation:
You may be ask to drink a contrast agent, like barium. This is a liquid that coats
the inside of your stomach and intestines, so they can be on a CT scan or X-ray image.
Barium may also be put in your rectum with a soft, small rubber tube. In some cases,
you may need to drink a liquid contrast agent the day before.
You’ll lie on a table. A radiation therapist uses a machine and the scans to find
exactly where the radiation will be aimed.
The therapist may mark your skin with tiny, long-lasting ink dots or tattoos. These
are used to aim the radiation at the exact same place each time.
Body molds might be made to help put you in the same position and stay still during
On the days you get radiation
Radiation treatment is like getting an X-ray. The radiation is stronger so it can
kill cancer cells. You can’t feel radiation, so the process will be painless. Also,
you will not be radioactive afterward.
On the days you have treatment, you’ll lie on a table. A radiation therapist may place
blocks or special shields to protect healthy parts of your body. The therapist then
lines up the machine. You may see lights and laser lines projected from the machine
lined up with the marks on your skin. These help the therapist know you are in the
right position. The radiation machine may be used to take X-rays or CT-scans before
treatment. This is done to help with alignment.
The therapist will leave the room while the machine sends radiation to your tumor.
The machine may whirr and buzz and will move, but it won't touch you. During this
time the therapist can see you, hear you, and talk to you. The treatment itself often
takes only a few minutes.
What to expect after radiation therapy
Radiation therapy affects normal cells as well as cancer cells. This can cause side
effects. The side effects depend on the amount and type of radiation. Some people
have few or no side effects. But if you have them, your doctor may change the dose
of your radiation or how often you have treatments. Or your doctor may stop treatment
until your side effects go away. Talk with your healthcare team about any side effects
Possible short-term side effects
These are some common short-term side effects:
Gas and bloating
Feeling the need to urinate often
Pain or burning feeling when you urinate or have a bowel movement
Blood in your stool
Trouble controlling your bowel movements
Feeling very tired
Low blood counts (seen on blood tests)
Skin irritation or skin changes in areas that get radiation
Some of these side effects can be controlled and even prevented with medicine. Most
get better over time after treatment ends, Some may be helped with diet. Talk with
your healthcare team about what side effects you should watch for, how to deal with
them, and how to know when they become serious. Make sure you know what number to
call with questions or problems. Is there a different number for evenings and weekends?
It may be helpful to keep a diary of your side effects. A written list will make it
easier to remember your questions when you go to appointments. It will also make it
easier for you to work with your healthcare team to make a plan to manage side effects.
Possible long-term side effects
Radiation therapy can cause some long-term side effects that may not show up until
many years after treatment. It depends on where the radiation was aimed and the dose
used. These can be more serious, so you should watch for them and talk with your healthcare
team about what to expect.
Long-term side effects can include:
Bowel or bladder irritation. You may feel the need to urinate or have bowel movements more often. You may also
have some pain with urination or bowel movements, or see blood in your urine or stool.
Be sure your doctor is aware of these problems so that they can be treated, if needed.
Early menopause (hormone changes) or infertility (inability to become pregnant). If you're a woman who hasn’t gone through menopause, you may have menopausal symptoms.
Talk with your doctor about what you can do to ease the symptoms.
Vaginal dryness. Women may have vaginal dryness and narrowing. This can lead to pain or bleeding during
sex. Lubricants can help with vaginal dryness. Vaginal narrowing may be helped by
using a vaginal dilator or by having sex. Both can help stretch the vagina.
Lower sperm count. Men may produce less semen. Their semen may have a lower sperm count. This could lower
a man's fertility. Still, it might be possible to get a woman pregnant. If you're
planning on having children, you may want to discuss saving sperm before starting
Erectile dysfunction. Men may have trouble getting or keeping erections. Certain drugs or a penile pump