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136 CHAPTER 4 Radiation Therapy and Surgery Radiation therapy, like chemotherapy, is intended to selectively kill malignant cells while sparing normal cells as much as possible. Like chemotherapy, radiation therapy (also called radiotherapy) is most active against rapidly dividing populations of cells. Unlike most forms of chemotherapy, radiation can be applied locally, to specific areas of the body, rather than spreading throughout the entire body via the bloodstream. Radiation therapy may be used alone to treat people with localized lymphocytepredominant Hodgkin lymphoma or localized indolent NHL, but it is more commonly used in combination with chemotherapy (a form of combined modality treatment). Combined modality therapy is most frequently used to treat localized disease, generalized disease in which there is a specific bulky component, or an area of localized disease that remains after chemotherapy treatment. Combined modality treatment, like combination chemotherapy, exploits the idea of hitting the cancer cells in different ways at the same time. Ionizing radiation kills cancer cells by creating free radicals, highly reactive substances that damage DNA and other cellular constituents. While this is similar to the mechanism by which many antineoplastic drugs work, there is a fundamental difference between using radiation and using drugs. Radiation is a completely different modality of treatment. Combined modality therapy typically does a better job of destroying cancer cells than either chemotherapy or radiation used alone, enabling the use of less radiation and less chemotherapy than would be necessary if either modality were used in isolation. However, the two modalities used together may be more toxic to healthy tissue as well as to cancer. Therefore, in deciding whether to use a Radiation Therapy and Surgery 137 V combined modality approach, your physician must carefully weigh the advantages against the disadvantages. Total body irradiation (TBI) is sometimes used to treat generalized disease in preparation for a stem cell transplant. Chemotherapy is more common as a first line of therapy to treat widespread disease, however, and radiation is most often used for treating localized areas of involvement. Several different kinds of radiation are used to treat lymphoma. Highenergy X-rays and gamma rays are used to treat tumors deep within the body. These high-energy forms of radiation penetrate some distance into the body before they interact with tissue. Electron beam therapy, which doesn’t penetrate as deeply, may be used to treat more superficial tumors. Ultraviolet light may be used to treat lymphomas such as mycosis fungoides that involve the skin. All these forms of radiation therapy are known as external radiation therapy , or external beam therapy, because you’re exposed to a beam of radiation emitted by a piece of equipment outside your body. Radiation can also be delivered internally by means of radioisotopes attached to monoclonal antibodies (see Chapter 5). External Beam Radiation Therapy External beam therapy may involve greater or lesser portions of your body. The size of the radiation field—and the duration of treatment—will depend on the extent of disease, the type of lymphoma, whether radiation is being used alone or in combination with chemotherapy, and whether the treatment is intended to be curative. In all cases, the treatment will be designed to minimize the exposure of healthy tissue to radiation. Involved site radiation therapy is delivered to sites of known disease. For people diagnosed with localized disease, this is determined on the basis of imaging studies done prior to treatment. For people diagnosed with widespread lymphoma, in which a particular region failed to respond to chemotherapy, the radiation field is determined by the extent of the remaining disease. In either case, the exact size of the radiation field will depend on the accuracy of the images, the likelihood that microscopic disease exists beyond the area of disease identified by CT, PET, or MRI, and what normal tissues are adjacent to the tumor. Radiation may be given alone as palliative treatment to people with widespread indolent NHL. In this case, the radiation is intended not to be U 138 Treating Lymphoma curative but to reduce the size of a particularly troublesome region of disease . Radiation therapy may be given with curative intent to people with localized low-grade NHL or localized lymphocyte-predominant Hodgkin lymphoma. Radiation therapy may also be used in combination with chemotherapy for people with Hodgkin lymphoma or some presentations of aggressive NHL. For example, people with very large mediastinal tumors (very large or “bulky” tumors are generally defined as those greater than 10 cm—about 4 inches—in diameter) are frequently treated...


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