• Types of radiotherapy
  
• External radiation therapy
  
• Radioimmunotherapy
  
• Interstitial therapy, brachytherapy
  

If you would like greater detail on radiation therapy, The Chemotherapy and Radiation Therapy Survival Guide, by Judith McKay, Nancee Hirano, Myles Lampenfeld, Making the Radiation Therapy Decision, by David Brenner and Eric Hall, and Coping with Radiation Therapy: A Ray of Hope, by Daniel Cukier and Virginia McCullough, are books that focus on radiation therapy from the patient's perspective.

Types of radiotherapy

There are several ways to administer radiation therapy:

• External radiotherapy, also called external beam irradiation, involving narrow x-ray beams aimed at your body while you lie on a table. This is the most common form of radiotherapy used for rectal cancer.

• Radioimmunotherapy, an injection of radioisotopes into a vein. The radioisotopes are attached to a carrier that homes preferentially to tumors instead of healthy tissue. The most common homing substances in use today are monoclonal antibodies, proteins produced by white blood cells and capable of traveling preferentially to tumors. Use of this technique against colon and rectal cancers is still in clinical trials.

• Intra-operative radiotherapy, which is aimed directly and only at the tumor bed, the empty spot in your body where the tumor once was. This is done while your body is still open during surgery, but after tumor removal. This technique is not discussed in this article, as the patient needn't prepare for or anticipate it in ways that differ from preparation for and anticipation of surgery.

• Brachytherapy, the positioning of a radioactive substance within the body very near or within the tumor. This technique might be used for rectal cancer, but not for colon cancer.

• Interstitial radiotherapy, involving implants of radioactive material, often permanent, stored in capsules, wires, or similar sealed delivery vehicles.

• Endocavitary radiation therapy, which utilizes a wand that emits radiation of very short wavelength that is placed in the rectum or vagina. This is expensive, specialized equipment that is not yet widely accessible, and is not discussed in this article as it is not often used for colorectal cancer.

External radiation therapy

The following sections will walk you through preparation and treatment simulation, scheduling, receiving therapy, departure, and the days that follow treatment.

Simulation

Several medical specialists are involved in this stage of your treatment: your radiation oncologist, the radiation therapy technician who will administer the treatment, a dosimetrist who calculates the correct dose, and the radiation physicist who calibrates the machine. Some of these staff members may work behind the scenes.

For these initial visits, which may be lengthy, make yourself as comfortable as possible by wearing clothing that doesn't bind, that goes on and off easily, and has no metal zippers. Bring a cassette player if you like, and use the restroom before the simulation starts.

None of these preparations are painful, but they may be embarrassing or unpleasant, for instance, if the staff decides that the best access to a rectal tumor is achieved by taping the buttocks into an open position, or if you are asked to drink a barium contrast solution to clarify the position of the small intestine.

Special shields or blocks may be made to shape the radiation beam to match exactly your tumor's shape, or the shape of nearby surgical scars. Beams of invisible radiation generated by the machinery are usually emitted shaped like rectangles, from two to fifteen inches in any dimension. If these beams were trained against your tumor, nearby healthy tissue within the two- to fifteen-inch rectangle would be irradiated, too, suffering damage. To avoid this effect, shields or blocks with cutaways in the silhouette of your tumor are created using your x-ray films as guides.

The shields made for you are used only by you. You may see the same kinds of devices belonging to other patients hanging nearby or in other treatment areas.

The machinery used during simulation looks and moves just as the genuine radiation equipment does, but instead it generates only a plain light beam to verify positioning, ink markings, and the fit of shields.

After all shields and blocks are made and your skin is marked, the entire simulation will be repeated with all pieces in place--exactly like a dress rehearsal.

As your treatment progresses and your tumor shrinks, new blocks may be made to match the new shape of your tumor, and these simulations may be repeated.

Preparation

Ask the medical staff about avoiding products such as skin lotion before treatment. They may interfere with treatment, or they may cause your skin to become hypersensitive if they are exposed to radiation. Ask as well about pacemakers, surgical staples, and clothing with metal zippers.

Scheduling

Dosage fractionation means that you will have to visit the treatment center several times a week, or perhaps every day, for several weeks, depending on your treatment plan. It also means that each dose of radiation lasts only two to four minutes. If your tumor is irradiated from several different angles (and most are), each angle may take two to four minutes after the machine is repositioned. After the lengthy time spent in simulation, you may feel that ten to thirty minutes of treatment time is an anticlimax.

Don't be surprised if the schedule on which your radiotherapy is administered differs from the schedules you hear others discussing, because your radiation schedule always is tailored to your particular circumstances, based on the size, number, and location of tumors; your overall health; your body size; and the type of cancer you have.

Depending on what treatments are being used, the timing of your radiation therapy may be influenced by the quantity of white blood cells remaining in your blood after your last chemotherapy or radiotherapy treatment. Your blood may be tested when you arrive, using a standard measurement known as a complete blood count, or CBC. If your white blood counts are too low, treatment may be delayed a few days or a week.

For each treatment, you might want to call the treatment center before leaving home or work. Radiation therapy machines sustain heavy use, and must be taken offline periodically for recalibration or repair. You can save time by calling first to see whether appointments are running on time.

After a few treatments, you may begin to feel that most of your time is spent traveling or chatting in the waiting room, because treatment itself is so brief.

Arrival

Ask your doctor if you should avoid possibly dangerous circumstances such as excessive sunlight or crowds.

Ask about skin care, too. External beam radiation must pass through your skin to reach tumor sites, and irritation may result. Newer, higher voltage equipment used today causes less damage to skin because the damaging rays concentrate in deeper layers, but some skin reaction still is possible, particularly in sensitive areas such as the skin between anus and genitals.

The setting

The room in which treatment is given has thick walls and is lead-clad to prevent the very small amount of radiation that bounces off your shields, known as scatter, from affecting the medical staff, those in the waiting room, and random passers-by. For the safety of the staff, the treatment room will contain only you when the machine is engaged. (The small dose of radiation they would sustain if they stayed with you would probably not harm them, but if they stayed with all patients, all day, every day, the dose from scatter would indeed accumulate to dangerous levels.)

The staff can see and hear you at all times, because there are microphones and cameras connecting you and them. If you feel at all bad, just let them know. Music and wall art sometimes are available in the treatment room to lower your boredom and stress levels.

Delivery of external radiation therapy

You may have your bladder filled with saline water prior to treatment in order to lift the small intestine away from the treatment area, thus protecting the small intestine.

You should feel no pain, no heat, no sensation at all during treatment, although some survivors say that they feel a sensation of energizing--not quite a tingling--in the area of the tumor during treatment. It may indeed be that some of us can sense a highly active biological entity such as a tumor reacting to the disruption of its DNA.

Some find the absence of sensation eerie, but most people are grateful that the treatment is comfortable and brief.

Dosages

A typical curative dosage for rectal cancer is 180 to 200 centiGreys (cGy) per day, repeated a few times a week for several weeks until a total dosage of 4,500 to 5,000 cGy is achieved. Additional radiation boosts of 540 to 900 cGy to smaller areas occupied or once occupied by tumor, called the tumor bed, are sometimes added. A variation sometimes introduced is delivering 120 to 160 cGy twice a day, 4 to 6 hours apart, for several weeks. In patients at high risk of recurrence of disease, a total of 6,000 to 7,000 cGy might be used in areas local to the tumor if the small bowel and other sensitive organs can be shielded. It's important to remember, though, that your radiation oncologist will adjust dosage to suit your individual needs.

If a higher dosage is required for certain sites, more sessions are added, but the dose per exposure is not raised. Because external beam radiation often must pass through healthy tissue to reach the site of the tumor, a moderate dose per exposure has been determined to be the best means for killing colorectal cancer cells while allowing healthy cells to recover.

Some patients question why lower doses over a longer period of time aren't used in order to reduce the side effects of treatment. Doses lower than those outlined above might allow a surge of cancer growth to go unchecked, as some researchers have noted accelerated growth in head and neck cancers apparently stimulated by radiotherapy. While this finding is not directly applicable to colon and rectal cancers, the risk of cancer regrowth after reducing the single fractionated dose is considered too great in the absence of more solid information.

Departure

You are not likely to feel unwell after your treatments, but if you do, do not leave without telling the medical staff of your problem.

Radioimmunotherapy

Radioimmunotherapy involves linking one molecule of a radioactive substance, a radioisotope such as iodine-131 or yttrium-90, to a monoclonal antibody. The proposed benefit of radioimmunotherapy over existing radiation treatments is that less healthy tissue is exposed to radiation because the antibody attaches preferentially to, but not only to, cancerous tissue. Some healthy tissue is affected because the radioactive substance decays as the antibody travels to the tumor and because monoclonal antibodies also will attach to some antigens on healthy cells, but it is thought that this effect is less than that sustained during external beam therapy. Radioimmunotherapy is administered into a vein, like chemotherapy.

The correct dose of radioimmunotherapy must first be determined. To calculate this dose, a small "tracer" amount of the substance will be injected first, and visualized using a CT scan or other imaging device. Based on what is seen, the doctors in charge will determine the total dose you should receive.

You will be kept in a lead-shielded hospital room throughout this treatment, and your body wastes will be disposed of in accordance with rules for handling hazardous waste. Face-to-face family visits will be very limited or denied entirely. The nurses who care for you may wear protective clothing and will limit contact with you.

If the radioisotope iodine-131 is to be used, your thyroid gland will be shielded first. The radioactive isotope, I-131, will destroy the thyroid gland if it is absorbed.

To shield the thyroid, large doses of nonradioactive iodine, iodine-123, are given to you first. This substance is taken up by the thyroid in excess compared to other body tissues. After the maximum amount has been absorbed, the thyroid cannot absorb more iodine for several days. This protects the thyroid gland from absorbing subsequent doses of I-131.

This method of treatment is not likely to be used for those who have had previous allergic reactions to iodine in shrimp, other foods, or in other medications.

Interstitial therapy, brachytherapy

Interstitial radiotherapy

Brachytherapy

Once the vessels are in place, the patient is returned to his hospital room. After sufficient healing, the patient is moved to a lead-shielded isolation room if not already so housed. A team specially trained to handle radioactive material arrives dressed in protective clothing to insert the radioactive substance into the vessel. It might be left in place for only a few minutes, or for a few hours, or a few days, depending on the dose required and the isotope used.

Typically, a high dose of radiotherapy for a short period is delivered by brachytherapy. This means that, while your body contains the radioactive substance, the radiation will pass through your tissues and will continue to travel beyond your body. Your bodily wastes might contain radioactive byproducts. Consequently, during this time you will represent a radiation hazard to others. Visits from family and friends will be discouraged or denied, and nursing staff will wear protective gear and limit their contact with you. They will provide you with all the care you need, but they may, for example, speak to you from the doorway instead of the bedside.