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For more than a century, the important biologic effects of ionizing radiation have been noted by scientists and have been applied clinically. Significant advances in technologic innovation coupled with radiobiologic research have firmly established radiation therapy as an important modality in cancer treatment. It may be used alone or in conjunction with other therapies in the management of a variety of conditions, both malignant and benign.

Radiation therapy can be delivered: (1) by external beam therapy; (2) by internal cavity placement of radionuclide sources, termed brachytherapy; or (3) by instillation of radionuclide solutions. These forms play significant roles in the treatment of various gynecologic malignancies (Table 28-1). For example, external beam therapy and brachytherapy are used in the primary management of inoperable cancers of the cervix, vagina, and vulva. Additionally, radiation therapy may be recommended as adjuvant treatment postoperatively if the probability of regional recurrence is high. For uterine malignancies, external beam therapy or brachytherapy may be recommended for adjuvant posthysterectomy treatment or can occasionally be used as a primary modality for inoperable tumors. For epithelial ovarian cancer, the indications for radiation therapy are few. Similarly, the role currently is limited for external beam therapy in the management of ovarian germ cell tumors and gestational trophoblastic neoplasia (Soper, 2003). Radiation therapy is used frequently in the relief of symptoms caused by metastasis of any gynecologic cancer. Accordingly, pain, bleeding, bronchial obstruction, and neurologic sequelae may often be effectively palliated.

Table 28-1. Role of Radiation Therapy in the Management of Gynecologic Cancers

Electromagnetic Radiation

Photons and gamma rays are the two types of electromagnetic radiation used in radiation therapy. Both can be considered as electromagnetic waves or as discrete particles (quanta) of energy. This duality is described in the wave-particle theory of quantum physics, which explains that energy can be transferred either by waves or particles.

Photons also known as x-rays are produced when a stream of electrons collides with a high atomic-number target, such as a tungsten target located in the head of a linear accelerator (Fig. 28-1). These photons are used in external beam therapy.

Figure 28-1

Block diagram of a linear accelerator used to create external beam radiation. Either photon beams or electron beams may be produced. A. Photon beam therapy is suited for deep tumors such as the cervical cancer shown here. Beam energy is measured in million volts (MV). B. Electron beam therapy is indicated for superficial lesions such as inguinal lymph nodes. Beam energy is measured in million electron volts ...

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