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Radiation therapy is any cancer treatment that involves killing tumor cells by exposing them to X-rays, gamma-rays, or electrons. There are several methods for administering radiation to a tumor. The most common method is to focus multiple X-ray beams on the tumor from different directions. This allows the radiation dose to be concentrated on the tumor while avoiding normal tissues as best as possible. This type of treatment is called "external beam radiation therapy."
Another form of radiation therapy is brachytherapy. Brachytherapy can be divided into two broad areas:
Injectable: This is when a radioactive compound is injected into a patient. The compound is selectively taken up by the tumor, giving a large dose of radiation to the tumor, but sparing the normal tissues throughout the body. For example, Iodine-131 can be used to treat thyroid tumors in dogs and cats.
Plesiotherapy: This is when a radioactive compound is placed on a superficial tumor in order to give a large dose of radiation to the area and spare as much of the normal underlying tissue as possible. For example, Strontium-90 can be used to treat nasal planum squamous cell carcinomas in cats.
All of these therapy options are available here at the University Of Tennessee College Of Veterinary Medicine.
Radiation therapy is very useful for controlling localized tumors. It can be given by itself but it is often used along with surgery and/or chemotherapy. Radiation may be administered either before or after surgery is performed - the best time to give radiation depends on the location, size, and type of cancer. Radiation can also be used along with chemotherapy to treat tumors such as lymphoma and melanoma. The optimal treatment may involve all three treatment modalities - surgery, chemotherapy, and radiation therapy.
Radiation therapy should not begin until complete staging of the disease has been completed. Staging refers to determining the extent of the disease in the patient's body. It is important to make sure there are no other tumors or metastases prior to therapy. Staging tests will be different for each tumor but they typically include a biopsy of the tumor, complete blood work, a urinalysis, radiographs of the chest, and an ultrasound of the abdomen. Some patients will require a CT scan or an MRI to determine the extent of the tumor or to plan radiation therapy.
Radiation therapy must be given over several days to avoid excessive damage to the normal tissue around the tumor. A typical course of therapy involves a single treatment given once a day, Monday through Friday, for approximately three or four weeks. The total number of treatments may vary depending on the type, location, and size of the tumor. To ensure that our patients remain absolutely still during therapy, they must be anesthetized for each treatment. Once anesthetized, our patients are placed on a treatment couch and positioned carefully to treat the tumor. The radiation treatment itself is painless, although side effects are expected. Once the treatment is completed, our patients wake up and may go home that day.
Any episode of anesthesia carries some risk. Fortunately, most of our patients are healthy aside from their tumor and have no greater risk for complications, even with daily anesthesia. Our anesthesia protocols are designed for smooth inductions and rapid recoveries; most patients are under for only 20-30 minutes and can go home soon after waking up. Our radiation technicians are trained and highly experienced in anesthesia and all of our patients are closely monitored.
No cancer therapy is completely free of side effects and radiation therapy is no exception. In fact, certain side effects are unavoidable but we can take steps to make them as mild and brief as possible. It is important to note that side effects only occur within the irradiated field and do not cause widespread problems. The types of side effects and the tissues that will be affected depend entirely on the area that is treated.
Side effects can be divided into two categories – acute and late side effects. Acute side effects are expected, are almost never life-threatening, and can be treated medically.
Acute side effects appear during the course of treatment and usually heal without complication by two weeks post-therapy.
Late side effects may appear 6 months to years after radiation therapy. It is very rare to see late side effects in our dogs and cats treated with radiation therapy. Late side effects usually cannot be treated so our radiation treatment protocols are designed to minimize the chance that they will occur.
Typical Acute Side Effects: Hair loss (alopecia), reddening of the skin (erythema), mild to moderate erosion of the skin (desquamation) or oral tissues (mucositis), eye irritation (keratitis).
Typical Late Side Effects: In most cases the benefits of radiation therapy outweigh the risks of possible side effects. Dr. Lee will be certain to discuss possible side effects at the time of your consultation.
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