![if !IE]> <![endif]>
In radiation therapy, ionizing radiation is used to interrupt cel-lular growth. More than half of patients with cancer receive a form of radiation therapy at some point during treatment. Radi-ation may be used to cure the cancer, as in Hodgkin’s disease, tes-ticular seminomas, thyroid carcinomas, localized cancers of the head and neck, and cancers of the uterine cervix. Radiation ther-apy may also be used to control malignant disease when a tumor cannot be removed surgically or when local nodal metastasis is present, or it can be used prophylactically to prevent leukemic in-filtration to the brain or spinal cord.
Palliative radiation therapy is used to relieve the symptoms of metastatic disease, especially when the cancer has spread to brain, bone, or soft tissue, or to treat oncologic emergencies, such as su-perior vena cava syndrome or spinal cord compression.
Two types of ionizing radiation—electromagnetic rays (x-rays and gamma rays) and particles (electrons [beta particles], protons, neutrons, and alpha particles)—can lead to tissue disruption. The most harmful tissue disruption is the alteration of the DNA mol-ecule within the cells of the tissue. Ionizing radiation breaks the strands of the DNA helix, leading to cell death. Ionizing radia-tion can also ionize constituents of body fluids, especially water, leading to the formation of free radicals and irreversibly damag-ing DNA. If the DNA is incapable of repair, the cell may die immediately, or it may initiate cellular suicide (apoptosis), a ge-netically programmed cell death.
Cells are most vulnerable to the disruptive effects of radiation during DNA synthesis and mitosis (early S, G2, and M phases of the cell cycle). Therefore, those body tissues that undergo fre-quent cell division are most sensitive to radiation therapy. These tissues include bone marrow, lymphatic tissue, epithelium of the gastrointestinal tract, hair cells, and gonads. Slower-growing tis-sues or tissues at rest are relatively radioresistant (less sensitive to the effects of radiation). Such tissues include muscle, cartilage, and connective tissues.
A radiosensitive tumor is one that can be destroyed by a dose of radiation that still allows for cell regeneration in the normal tis-sue. Tumors that are well oxygenated also appear to be more sen-sitive to radiation. In theory, therefore, radiation therapy may be enhanced if more oxygen can be delivered to tumors. In addition, if the radiation is delivered when most tumor cells are cycling through the cell cycle, the number of cancer cells destroyed (cell-killing) is maximal.
Certain chemicals, including chemotherapy agents, act as radio-sensitizers and sensitize more hypoxic (oxygen-poor) tumors to the effects of radiation therapy. Radiation is delivered to tumor sites by external or internal means.
If external radiation therapy is used, one of several delivery methods may be chosen, depending on the depth of the tumor. Depending on the amount of energy they contain, x-rays can be used to destroy cancerous cells at the skin surface or deeper in the body. The higher the energy, the deeper the penetration into the body. Kilovoltage therapy devices deliver the maximal radiation dose to superficial lesions, such as lesions of the skin and breast, whereas linear accelerators and betatron machines produce higher-energy x-rays and deliver their dosage to deeper structures with less harm to the skin and less scattering of radia-tion within the body tissues. Gamma rays are another form of energy used in radiation therapy. This energy is produced from the spontaneous decay of naturally occurring radioactive ele-ments such as cobalt 60. The gamma rays also deliver this radi-ation dose beneath the skin surface, sparing skin tissue from adverse effects.
Some centers nationwide treat more hypoxic, radiation-resistant tumors with particle-beam radiation therapy. This type of ther-apy accelerates subatomic particles (neutrons, pions, heavy ions) through body tissue. This therapy, which is also known as high linear energy transfer radiation, damages target cells as well as cells in its pathway.
A few centers are using intraoperative radiation therapy (IORT), which involves delivering a single dose of high-fraction radiation therapy to the exposed tumor bed while the body cav-ity is open during surgery. Cancers for which IORT is being used include gastric, pancreatic, colorectal, bladder, and cervical can-cers and sarcomas. Toxicity with IORT is minimized because the radiation is precisely targeted to the diseased areas, and exposure to overlying skin and structures is avoided.
Internal radiation implantation, or brachytherapy, delivers a high dose of radiation to a localized area. The specific radio-isotope for implantation is selected on the basis of its half-life, which is the time it takes for half of its radioactivity to decay. This internal radiation can be implanted by means of needles, seeds, beads, or catheters into body cavities (vagina, abdomen, pleura) or interstitial compartments (breast). Brachytherapy may also be administered orally as with the isotope I131, used to treat thyroid carcinomas.
Intracavitary radioisotopes are frequently used to treat gyne-cologic cancers. In these malignancies, the radioisotopes are inserted into specially positioned applicators after the position is verified by x-ray. These radioisotopes remain in place for a pre-scribed period and then are removed. Patients are maintained on bed rest and log-rolled to prevent displacement of the intracavitary delivery device. An indwelling urinary catheter is inserted to en-sure that the bladder remains empty. Low-residue diets and anti-diarrheal agents, such as diphenoxylate (Lomotil), are provided to prevent bowel movement during therapy, to prevent the radio-isotopes from being displaced.Interstitial implants, used in treating such malignancies as prostate, pancreatic, or breast cancer, may be temporary or per-manent, depending on the radioisotopes used. These implants usually consist of seeds, needles, wires, or small catheters posi-tioned to provide a local radiation source and are less frequently dislodged. With internal radiation therapy, the farther the tissue is from the radiation source, the lower the dosage. This spares the noncancerous tissue from the radiation dose.
Because patients receiving internal radiation emit radiation while the implant is in place, contacts with the health care team are guided by principles of time, distance, and shielding to mini-mize exposure of personnel to radiation. Safety precautions used in caring for the patient receiving brachytherapy include assigning the person to a private room, posting appropriate notices about ra-diation safety precautions, having staff members wear dosimeter badges, making sure that pregnant staff members are not assigned to this patient’s care, prohibiting visits by children or pregnant vis-itors, limiting visits from others to 30 minutes daily, and seeing that visitors maintain a 6-foot distance from the radiation source.
The radiation dosage is dependent on the sensitivity of the target tissues to radiation and on the tumor size. The lethal tumor dose is defined as that dose that will eradicate 95% of the tumor yet preserve normal tissue. The total radiation dose is delivered over several weeks to allow healthy tissue to repair and to achieve greater cell kill by exposing more cells to the radiation as they begin active cell division. Repeated radiation treatments over time (fractionated doses) also allow for the periphery of the tumor to be reoxygenated repeatedly because tumors shrink from the outside inward. This increases the radiosensitivity of the tumor, thereby increasing tumor cell death.
Toxicity of radiation therapy is localized to the region being irra-diated. Toxicity may be increased when concomitant chemother-apy is administered. Acute local reactions occur when normal cells in the treatment area are also destroyed and cellular death exceeds cellular regeneration. Body tissues most affected are those that normally proliferate rapidly, such as the skin, the epithelial lining of the gastrointestinal tract, including the oral cavity, and the bone marrow. Altered skin integrity is a common effect and can include alopecia (hair loss), erythema, and shedding of skin (desquama-tion). After treatments have been completed, reepithelialization occurs.
Alterations in oral mucosa secondary to radiation therapy in-clude stomatitis, xerostomia (dryness of the mouth), change and loss of taste, and decreased salivation. The entire gastrointestinal mucosa may be involved, and esophageal irritation with chest pain and dysphagia may result. Anorexia, nausea, vomiting, and diarrhea may occur if the stomach or colon is in the irradiated field. Symptoms subside and gastrointestinal reepithelialization occurs after treatments are complete.
Bone marrow cells proliferate rapidly, and if bone marrow– producing sites are included in the radiation field anemia, leukope-nia (decreased white blood cells [WBCs]), and thrombocytopenia (a decrease in platelets) may result. Patients are then at increased risk for infection and bleeding until blood cell counts return to normal. Chronic anemia may occur. Research continues to de-velop radioprotective agents that can protect normal tissue from radiation damage.
Certain systemic side effects are also commonly experienced by patients receiving radiation therapy. These manifestations, which are generalized, include fatigue, malaise, and anorexia. This syndrome may be secondary to substances released when tumor cells break down. The effects are temporary and subside with the cessation of treatment.
Late effects of radiation therapy may also occur in various body tissues. These effects are chronic, usually produce fibrotic changes secondary to a decreased vascular supply, and are irre-versible. These late effects can be most severe when they involve vital organs such as the lungs, heart, central nervous system, and bladder. Toxicities may intensify when radiation is combined with other treatment modalities.
The patient receiving radiation therapy and the family often have questions and concerns about its safety. To answer questions and allay fears about the effects of radiation on others, on the tumor, and on the patient’s normal tissues and organs, the nurse can ex-plain the procedure for delivering radiation and describe the equipment, the duration of the procedure (often minutes only), the possible need for immobilizing the patient during the proce-dure, and the absence of new sensations, including pain, during the procedure. If a radioactive implant is used, the nurse informs the patient and family about the restrictions placed on visitors and health care personnel and other radiation precautions. Pa-tients also need to understand their own role before, during, and after the procedure.
The nurse assesses the patient’s skin, nutritional status, and gen-eral feeling of well-being. The skin and oral mucosa are assessed frequently for changes (particularly if radiation therapy is directed to these areas). The skin is protected from irritation, and the pa-tient is instructed to avoid using ointments, lotions, or powders on the area.
Gentle oral hygiene is essential to remove debris, prevent irri-tation, and promote healing. If systemic symptoms, such as weak-ness and fatigue, occur, the patient may need assistance with activities of daily living and personal hygiene. Additionally, the nurse offers reassurance by explaining that these symptoms are a result of the treatment and do not represent deterioration or pro-gression of the disease.
When a patient has a radioactive implant in place, nurses and other health care providers need to protect themselves as well as the patient from the effects of radiation. Specific instructions are usually provided by the radiation safety officer from the x-ray de-partment. The instructions identify the maximum time that can be spent safely in the patient’s room, the shielding equipment to be used, and special precautions and actions to be taken if the im-plant is dislodged. The nurse should explain the rationale for these precautions to keep the patient from feeling unduly isolated.
Copyright © 2018-2023 BrainKart.com; All Rights Reserved. Developed by Therithal info, Chennai.