EXTERNAL BEAM RADIATION THERAPY
External beam radiation therapy is used for rectal cancer, and in most cases of advanced-stage colon cancer. A full course of external beam radiation therapy takes four to six weeks of daily treatments. The goal is to deliver the best dose to the affected area, with the least impact on the surrounding normal tissues.
This is accomplished by aiming the treatment beam at the cancer area from different angles. In this manner, the impact on healthy tissue is diminished by being spread over a large volume, while the effect on the target area, where the beams intersect, is increased. This requires an approach carefully tailored to each case.
Using a simulation unit, the radiation oncology staff will determine the best angles for the beam. Then they will outline the treatment ports— places on your body where the beam will be aimed. These ports will be marked with colored ink or by tiny tattoos. These markings will ensure that the beam is aimed accurately every treatment session.
The simulation may take several hours. The information obtained will be entered into a computer to develop your treatment plan. Sometimes a special cast will be fabricated for you to ensure consistent positioning. Once the planning is completed, the treatments can begin.
IMRT, or intensity modulated radiation therapy, is an advanced technique that is being used more frequently in treating rectal cancer. IMRT treatment is carefully planned using sophisticated software, to plan a precise dose of radiation in three dimensions, based on a tumor’s size, shape and location.
The high doses of radiation are tightly focused on the tumor, limiting exposure to much of the nearby healthy tissue.
HOW TREATMENT IS GIVEN
Radiation therapy is usually started five to seven weeks after surgery. The full course of treatment runs four to six weeks, with sessions from Monday through Friday, and rest and recovery periods during weekends.
Typically, you will arrive at the facility at the appointed time each day. You may want to bring a friend for moral support, or an iPod or a book to help pass the time in case you have to wait.
The treatment is given in a room that has thick concrete walls and lead-lined doors, to protect those who are outside the treatment area from radiation.
The device used to deliver radiation is called a linear accelerator. At first the whole set up may seem complex and intimidating. But don’t be alarmed. A TV monitor lets the staff keep you in sight at all times, in case you need anything.
The radiation therapist will adjust the position of the machine according to the previously determined settings, then step out of the room. During the actual exposure you must remain as still as possible. The unit will be repositioned one or two times to change the angle of the beam. Each exposure lasts only a few minutes and you won’t see or feel anything.
SIDE EFFECTS OF EXTERNAL BEAM RADIATION THERAPY
Radiation therapy is a safe, proven treatment, but it does have a few unwanted side effects. Most of them are due to the fact that the radiation beam affects normal tissues around the tumor area—most importantly, the large and small bowel, and the bladder. So the most common side effects include diarrhea, nausea, vomiting, and bladder irritation. You might also experience fatigue and skin changes in the area where the beam impacts the skin on your abdomen. The side effects vary from patient to patient and according to the exact location of the radiation.
Fatigue is often due to stress related to your illness, daily trips for treatment, and the effects of radiation on normal cells. Most people begin to feel tired after a few weeks of radiation therapy. You can help yourself by not trying to do too much. If you feel tired, limit your activities, use your leisure time in a restful way, and try to get more sleep at night. If you continue working a full-time job while undergoing radiation therapy, talk with your employer about adjusting your work schedule, or try working at home for a period of time.
The energy waves used in radiation therapy have an effect on the skin that resembles the effect of intense sunlight. Some skin irritation and redness, similar to a sunburn, may develop by the third or fourth week of treatment. Don’t rub or scratch the affected area. Use mild soap, being careful not to wash off port markings, if you have any. Wear soft clothing, preferably cotton, and protect the treated area from sunlight. Advise your doctor or nurse at once if your skin cracks or blisters, so that they can instruct you on proper care.
Other Side Effects
If you develop diarrhea as a result of bowel irritation by the radiation beam, ask your physician to recommend a diet that is less irritating to the bowel. Avoid spicy foods, and concentrate instead on easily digestible foods that are not excessively high on roughage.
Radiation colitis (inflammation of the colon) can become a chronic (permanent) problem for many people who receive radiation therapy to treat cancer in the abdomen. Complications of chronic radiation colitis may include some of the following:
• Deep ulcers in the lining of the colon. The ulcers may bleed, causing
blood in the stools. Prolonged bleeding can lead to anemia (low red blood
cell count), which can cause weakness and extreme tiredness.
• Ulcers may tunnel through the affected area into surrounding tissues
such as the bladder, vagina, or skin. The anus and rectum are often
involved. The tunnels, called fistulas, often become infected.
• Damaged tissue in the colon may gradually be replaced with scar tissue, which cannot absorb nutrients from food, possibly leading to protein and vitamin deficiency.
• Scar tissue may cause bowel obstruction, which usually requires surgical treatment.
In men, radiation treatment to the pelvis damages the blood vessels necessary to achieve an erection, and, particularly in older men, may result in erectile dysfunction—inability to achieve an erection.