Radiation Therapy
Jennifer Dunn Bucholtz
Michele A. Parisi
I. History:
In the late 1890s, x-rays and gamma rays were discovered by Roentgen and Curie. By the early 1900s, ionizing radiation was being used to treat a variety of neoplasms. Since that time, the ability to precisely aim radiation at tumors, minimize radiation delivery to normal tissues, and manage the side effects of treatment has greatly improved.
II. Definition:
Radiation is the movement of energy through a space or medium. It causes damage or changes to the cells. Radiation therapy is a major cancer treatment that can be used alone or in combination with other therapies to cure, control, or palliate disease. It is estimated that over 50% of all people with cancer will receive radiation therapy during treatment for their disease. Radiation therapy is also used occasionally to treat benign tumors.
III. Rationale for Use:
When radiation is well planned and executed, cancer cells are killed or left unable to reproduce while the surrounding healthy cells are minimally affected and can repair radiation damage.
IV. Biology of Therapy:
Ionizing radiation includes x-rays and gamma rays, which are energy sources in wave formation, and particle radiation (electrons, beta, or protons). Each form causes damage or changes to cells that are penetrated, and DNA is directly or indirectly damaged.
A. Cell Cycle Phase: Cells are more sensitive to radiation during the late G2 and early M phases.
B. Degree of Oxygenation: Well-oxygenated tumor cells are more sensitive to radiation than hypoxic cells.
C. Tumor Size: Small tumors are more responsive than large tumors.
D. Cell Ability to Repair Damage: When treated appropriately, tumor cells are not able to repair radiation damage as well as surrounding normal cells.
E. Dose and Fraction Size of Radiation: Normal cells are able to repair radiation injury between fractionated doses better than tumor cells.
F. Types of Radiation: The radiation source may be external or internal. Beam characteristics vary with the source of radiation and allow maximum treatment of different tumor types (Table 8-1).
V. Types of Radiation Therapy
A. External beam radiation is an external source of radiation in the form of x-rays, gamma rays, protons, or electrons. The source is emitted from equipment that delivers radiation to the depth appropriate for each tumor. Treatment may be administered one or more
times a day. The number of treatments is determined by the size and location of the tumor and the total dose required (see Table 8-1).
times a day. The number of treatments is determined by the size and location of the tumor and the total dose required (see Table 8-1).
TABLE 8-1 Radiation Source, Delivery Mode, and Characteristics | |||||||||||||||||||||||||||||||||
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B. Internal radiation is placed in or near the tumor. The source may be a sealed isotope, placed in the body, or the systemic administration of an unsealed radionuclide, given orally, intravenously, or into a body cavity.
C. Methods of Administration
1. Intraoperative treatment exposes the localized tumor or tumor bed to electrons or orthovoltage during the surgical procedure.
2. Hyperthermia raises the body temperature and increases perfusion of the radioactive substance at the tumor site for a defined period of time.
3. Radioimmunotherapy allows selective delivery of radionuclide isotopes within the tumor.
4. Radiosensitizers are chemical agents given to increase sensitivity to radiation.
5. Radioprotectors are chemical agents that decrease the effects of radiation on normal tissue.
6. Hyperfractionation uses smaller, more frequent doses of radiation to impact on cancer cells as they divide and grow.
7. Total body irradiation cleanses the body of any tumor cells before the infusion of healthy bone marrow.
8. Stereotactic radiosurgery is the precise delivery of radiation to a brain tumor with sparing of surrounding normal tissue. To achieve precision, special procedures for localization of the tumor are necessary. These tools include the stereotactic frame, the computed tomography (CT) and magnetic resonance imaging (MRI) scanner, a computerized system for calculating the radiation dose, and a precise system for delivering the radiation to the tumor.
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