After a physician has determined that radiation therapy is appropriate, the patient will be referred to a radiation oncologist for a series of planning sessions. The oncologist will receive vital information about the patient’s condition, including the results from any scans, pathology reports, surgeries or procedures. The oncologist will consult with other professionals involved in the treatment who are a part of the patient’s cancer care team. Radiation therapy is usually performed at a hospital or medical facility, often one that specializes in cancer treatment.

After reviewing the information, the radiation oncologist will decide which method of radiation will be best. The choice to use external radiation therapy will lead to a process called simulation (sometimes called a marking session). During this process, the physician will use a special x-ray machine that resembles the machine that is used in the actual therapy. With the help of a specialized radiation technician, the physician will:

• Check tumor size (if present)
• Identify areas where the cancer may have spread
• Identify normal tissues in the treatment area
• Take measurements
• Mark the area to be radiated

After simulation, the physician will determine the amount of radiation to be delivered. A clinical physicist gives advice on technical matters regarding the radiation therapy, and a dosimetrist helps design the treatment plan customized to the patient’s needs.

Radiation dosage is measured by the amount of radiation absorbed by the tissues. Scientists use a unit known as a gray (Gy) to calculate this measurement and different tissues can tolerate different amounts of radiation measured in centigrays (cGy). For example, the liver can tolerate 3,000 cGy, the lungs 2,000 cGy and the kidneys 1,800 cGy.

The physician will use a therapeutic ratio to calculate the most effective dosage level. The therapeutic ratio compares the damage inflicted on cancer cells with the damage likely to occur to normal cells. Once a total dosage amount has been selected, it is divided into smaller amounts that are administered over individual treatment sessions. This is called the fractionation schedule, and it allows the physician to maximize the treatment’s ability to kill cancer cells while minimizing any incidental damage to normal cells by giving the body rest periods to recover.

Prior to beginning treatment, patients also may receive long-lasting, but tiny tattoo marks at the spot where the radiation is to be delivered. This will ensure that the radiation is directed precisely at the appropriate target during each treatment session. The tattoos provide important placement information should any future radiation be necessary. Prior to treatment, the physician may create a mold or device to help keep the patient in the proper place during the sessions. It also helps ensure that only the targeted area is treated.

During an external beam radiation treatment session, the patient is placed in the proper position using predetermined measurements and molds, if necessary. Radiation shields may be placed to protect areas that are not part of the treatment. As the radiation is delivered, the machine being used for the procedure may be rotated around the patient’s body to deliver radiation from different angles. A treatment session typically lasts for 15 to 20 minutes, although the actual radiation exposure time is much less.

External radiation treatments typically are scheduled on a daily basis, five days a week over a period of five to seven weeks. In some cases, patients will be treated twice daily.

Patients who receive internal radiation therapy will likely have the radiation source placement performed in a single session. If the placement is temporary, it will be removed anywhere from several minutes to a few days after it has been inserted.

The dosage and schedule for temporary brachytherapy varies depending on several factors, including the type and location of the cancer. In high-dose rate (HDR) brachytherapy, the patient may receive short, intense sessions that are repeated several times a day. HDR brachytherapy may continue for one to two weeks before the implant device is removed.

Low-dose rate (LDR) brachytherapy provides a continuous dose of radiation over several hours or days. These patients may be required to remain in the hospital during the treatment period until the device is removed.

Radiation therapy is usually performed on an outpatient basis, with most patients returning home after the procedure. However, some patients may be required to remain in the hospital for a short stay. Patients who have internal radiation therapy may be restricted from some degree of exposure to others for a short period of time. This is to prevent others from coming into contact with radiation that may escape from the body.