Radiation therapy is one way to treat anal cancer. It uses strong rays of energy to destroy and control the growth of cancer cells. This is a local treatment. That means it affects the cells only in the area that's treated.

To get this treatment, you'll see a radiation oncologist. This doctor specializes in the use of radiation therapy to kill cancer cells. The doctor decides what kind of radiation you need, how often you need it, and what dose should be used.

Radiation therapy may be a part of your treatment plan for anal cancer in several situations:

• It is most commonly used as the main treatment at the same time as chemotherapy in order to treat anal cancer. This often can help to cure it. This is called chemoradiation.
• It may be given after surgery to kill any cancer cells that may be left in your body.
• It might be used to treat anal cancer that has come back in nearby lymph nodes after treatment.
• It can be used to ease tumor symptoms, such as blockages or pain, if the cancer isn't responding to treatment. This is called palliative therapy.

External beam radiation therapy (EBRT) is commonly used. It focuses radiation onto the anal cancer from outside of the body. The preferred type of EBRT is called intensity-modulated radiation therapy (IMRT). IMRT is a special form of 3D conformal radiation therapy. It uses a computer-driven machine to deliver a specific dose of radiation from several angles to the specific shape of your treatment area. IMRT allows a higher dose of radiation to be given while limiting radiation to normal tissues.

Radiation treatment is most often given 5 days a week, Monday through Friday, for 5 to 6 weeks.

Another type of EBRT is called stereotactic body radiation therapy (SBRT). It may be used when cancer comes back in the same place, to treat nearby lymph nodes, and in areas like the brain. You may only be given 1 to 5 treatments.

Before you start treatment, your doctor will do imaging scans called a simulation scan. This is to measure the tumor ahead of time, so the beams of radiation can be exactly focused there. You may be on your back or, more commonly, your belly during treatment. Your doctor may put small marks on your skin to mark the treatment area. These marks might be made with permanent ink or tiny tattoos. They're used to make sure you are being set up the same way every day and the radiation is being given to the same region each time. A mold or cast might also be made to hold you still and in the exact same position for each treatment.

On each day of treatment, you'll likely be asked to have a full bladder before treatment is given. You're carefully put into the right position. You may see lights from the machine lined up with the marks on your skin. These help the radiation therapist know the radiation is going to the right place. The machine moves but doesn't touch you during the treatment. You can't see or feel the radiation. It's a lot like getting an X-ray, but it takes longer.

During the actual treatment, the therapist will leave the room while the machine sends radiation to the cancer. During this time, the therapist can see you, hear you, and talk to you. When the machine sends radiation to your tumor, you'll need to be very still. But you don't have to hold your breath. Treatment lasts only a few minutes, and the whole process will likely take less than an hour.

Radiation affects both normal cells and cancer cells. This means it can cause side effects. Some start during treatment, called short-term side effects, while others start later and can last the rest of your life, called late side effects. Most side effects can be treated. And there may be things you can do to help prevent some.

Most side effects start a few weeks into treatment and go away over time after treatment ends. Here are some common short-term side effects of radiation therapy for anal cancer:

• Skin irritation, redness, blistering, itching, or burning in the treated area around the anus
• Anal irritation and pain
• Diarrhea, sometimes with some rectal bleeding
• Discomfort when having a bowel movement
• Nausea and vomiting
• An urgent need to urinate, burning with urination
• Bladder pain
• Tiredness (fatigue)
• Low blood cell counts

Here are some possible long-term side effects of radiation for anal cancer:

• Scar tissue that forms and causes problems with bowel movements or bowel obstructions
• Inability to have children (infertility)
• Impotence (erectile dysfunction)
• Damage to the pelvic bones, increasing the risk for fractures or breaks
• Damage to blood vessels in the rectum, which can cause rectal pain and bleeding (chronic radiation proctitis)
• Vaginal dryness and narrowing and shortening of the vagina (vaginal stenosis)
• Connections (fistulas) appear between the bowel and vagina

Talk to your health care team about side effects you could have and what you should watch for. Ask when you need to report side effects to your health care team.

It's important to know how the radiation therapy will work and what side effects you might have. Ask what can be done to help prevent or ease them. Also know which side effects are short-term and which could occur later on and affect the rest of your life. Many of the side effects during treatment can be treated, so it's important to tell your health care team about your side effects.

Talk with your health care team about what signs to look for and when to call them. For instance, radiation for anal cancer can cause diarrhea, bleeding, and other bowel problems. Know what number to call with questions. Is there a different number for evenings, weekends, and holidays?

It may be helpful to keep a diary of your side effects. Write down physical, mental, and emotional changes. A written list will make it easier for you to remember your questions when you go to your appointments. It will also make it easier for you to work with your health care team to make a plan to manage your side effects.