Radiation therapy is the use of high energy, penetrating radiation (x rays, gamma rays, proton rays, and neutron rays) to kill cancer cells.
The primary purpose of radiation therapy is to eliminate or shrink localizedcancers (as opposed to cancers that have spread to distant parts of the body). The aim is to kill as many cancer cells as possible, while doing as littledamage as possible to healthy tissues. In some cases, the purpose is to killall cancer cells and effect a cure. In other cases, when cures are not possible, the purpose is to alleviate pain by reducing the size of tumors that cause pain.
For some kinds of cancers (for example, Hodgkin's disease, non-Hodgkin's lymphoma, prostate cancer, and laryngeal cancer), radiation therapy alone is thepreferred treatment. However, radiation is often used in conjunction with surgery, chemotherapy, or both, and survival rates for combination therapy in these cases are greater than for any single type of therapy. Radiation therapyis especially useful when surgical procedures cannot remove an entire tumor without damaging the function of surrounding organs. In these cases, surgeonsremove as much of the tumor as possible, and the remainder is treated with radiation (irradiated).
Radiation therapy is also known as radiotherapy, radiation treatment, x ray therapy, cobalt therapy, and electron beam therapy. Recent advances have madeit even more useful for patients and have cut down on some of the unpleasantside effects. Radioactive implants allow delivery of radiation to localized areas, with less injury to surrounding tissues than radiation from an externalsource that must pass through those tissues. Proton radiation also causes less injury to surrounding tissues than traditional photon radiation because proton rays can be more tightly focused. Current research with radioimmunotherapy and neutron capture therapy may provide ways to direct radiation exclusively at cancer cells, and in the case of radioimmunotherapy, to cancer cells that have spread to many sites throughout the body.
High energy radiation kills cells by damaging their DNA and thus blocking their ability to divide and proliferate. Radiation kills normal cells about as well as cancer cells, but cells that are growing and dividing quickly (such ascancer cells, skin cells, blood cells, immune system cells, and digestive system cells) are most susceptible to radiation. Fortunately, most normal cellsare better able to repair radiation damage than are cancer cells. Accordingly, radiation treatments are parceled into component treatments that are spaced throughout a given time interval (usually about seven weeks). Thus, cells are given a chance to repair during the time between treatments. Since the repair rate of normal cells is greater than the repair rate of cancerous cells,a smaller fraction of the radiation-damaged cancerous cells will have been repaired by the time of the next treatment. This procedure is called "fractionation" because the total radiation dose is divided into fractions. Fractionation allows greater killing of cancer cells with less ultimate damage to the surrounding normal cells. Ideally all cancer cells will be dead after the lasttreatment session.
Before radiation therapy, the size and location of the patient's tumor and the nature of the surrounding tissue that may be in the path of the radiation beam must be determined as accurately as possible so that the radiation treatment can be designed to be maximally effective. Magnetic resonance imaging (MRI) and computed tomography scan (CT scan) are used to provide detailedimages. The correct radiation dose, the number of sessions (fractions), theinterval between sessions, and whether to give each fraction from the same direction or from different directions to lower the total dose imparted to anyone nearby area, are calculated based on the tumor type, its size, and the sensitivity of the nearby tissues.
Shields are sometimes constructed for the patient to protect certain areas. The patient's skin may be marked with ink or tattoos to help achieve correct positioning for each treatment, or molds may be built to hold tissues in exactly the right place each time. When treatment may cause hair loss, some patients may want to purchase a wig, hat, or bandana in advance.
Follow-up is important for patients who have received radiation therapy. Theyshould go to their radiation oncologist at least once within the first several weeks after their final treatment to see if their treatment was successful. They should also see an oncologist every six to twelve months for the restof their lives so they can be checked to see if the tumor has reappeared or spread.
Treatment of symptoms following radiation therapy depends on which part of the body is being treated and the type of radiation. Nevertheless, many patients experience skin burn, fatigue, nausea, and vomiting regardless of the treatment area.
Affected skin should be kept clean and can be treated like a sunburn, with skin lotion or vitamin A and D ointment. Patients should avoid perfume and scented skin products and protect affected areas from the sun.
Nausea and vomiting are expected when the dose is high or if the abdomen or another part of the digestive tract is irradiated. Sometimes nausea and vomiting occur after radiation to other regions, but in these cases the symptoms usually disappear within a few hours after treatment. Nausea and vomiting can be treated with antacids, Compazine, Tigan, or Zofran.
Fatigue frequently starts after the second week of therapy and may continue until about two weeks after the therapy is finished. Patients may want to limit their activities, cut back their work hours, or take time off from work. They also may need to take naps and get extra sleep at night.
Patients who receive external beam therapy do not become radioactive and should be assured that they do not pose a danger to others. However, some patients who receive brachytherapy go home with low levels of radioactivity inside their bodies. These patients should be given instructions about any dangers they might pose to children and people of child-bearing age and how long thesedangers will last.
Emotional support is an important part of the care for patients undergoing any treatment for cancer.