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How does radiation therapy work?
Radiation, at levels thousands of times the amount used to produce a chest x-ray, destroys the ability of cells to divide and grow. Both normal and cancer cells are affected, but the radiation treatment is designed to maximize tumor effect and minimize normal tissue effect. Maximizing tumor effect is one reason radiation therapy is given in a series of treatments rather than one treatment.
What are the benefits of radiation therapy?
Radiation therapy can offer, in some instances, permanent control of tumors that cannot be controlled by surgery or chemotherapy,. In other cases, even when cure is not possible, radiation therapy can still bring a measure of relief. Shrinking a large tumor with radiation therapy may improve the quality of life by reducing pressure, bleeding or pain.
Are there risks involved?
There are some risks involved with any type of treatment for cancer. In addition to cancer cells, some normal cells will also be killed by the radiation. Some side effects may be apparent because of these normal cells being killed. Usually these side effects are temporary and outweighed by the benefits of killing cancer cells.
In addition, radiation therapy requires that the animal be perfectly still during treatment. Thus, general anesthesia is necessary for each treatment. There is always a slight risk associated with general anesthesia, but nearly all cancer patients accommodate to this aspect of the treatment very well.
How is the radiotherapy given?
High energy radiation is directed at the cancer and some normal tissue around it. At the UW-Madison's Veterinary Medical Teaching Hospital, a cobalt machine is used. When the cobalt machine is turned on, a source of radioactive cobalt moves over an opening in the storage head and the high energy radiation is directed onto the patient. Each treatment takes 5-10 minutes. When the daily treatment is completed, no radioactivity remains in the body.
Is radiation therapy ever used in combination with chemotherapy?
Yes, in situations where it is unlikely that any one method of cancer treatment will be effective (such as bulky or aggressive tumors), radiation therapy can be combined with chemotherapy or surgery. In some situations, combining all three types of treatment may be recommended. Details concerning these combinations can be provided by the cancer specialist.
Who gives radiation therapy treatment?
A cancer specialist will determine if radiation therapy will be useful for treatment of your pet's cancer. If so, a veterinarian specially trained in radiation therapy will carefully plan the treatment. Treatment for each patient is different. The radiation therapist (also called a radiation oncologist) will supervise the first radiation therapy treatment so that it is clear to everyone involved exactly how the treatment is to be given. After the first radiation therapy treatment, additional treatments will be given by a radiation therapy technologist. These individuals have had special training in the administration of radiation for cancer treatment.
Is radiation therapy expensive?
Radiation therapy can be costly because it involves complex equipment plus the expertise of many health care professionals. While the cost varies with the type and number of treatments required, you can expect to spend at least $900 - $3,500.
How long does the treatment take?
Radiation therapy is given in a series of treatments that encompass two to five weeks. This schedule helps protect normal healthy tissue by spreading out the total dose of radiation. The total dose used and the number of treatments, called fractions, in which the total dose is given depend on many factors. These factors include size and location of the cancer, the general health of your pet, and the type of cancer present.
What are the effects of treatment?
During treatment, the cancer specialist will monitor the effect of the radiation on the cancer as well as on normal tissue. It may be necessary to alter the plan because of changes in the tumor or normal tissue, but this is usually not necessary. Most side effects that occur during radiation therapy, although unpleasant, are usually not serious.
Many animals develop skin changes in the area being treated. A redness of the skin may develop near the end of, or after, radiation therapy. This may progress to skin moistness, similar to eczema. This moistness may cause the animal to scratch, but it is important not to allow the pet to do so. Medication and/or physical means to prevent scratching may be prescribed by the veterinarian. It is not advisable for you to purchase over-the-counter drugs and treat these conditions yourself unless instructed to do so by your veterinarian. This skin moistness and itching will usually subside in 7-10 days. Hair loss in the treated area is common. This will occur after the radiation therapy is over. Hair loss in the treated area may persist for some time, but hair regrowth occurs in most patients. The color of the regrowing hair and skin in the treated area are likely to change. Dark hair and skin usually become lighter in color while light skin and hair may become darker.
It is unusual for animals to become nauseated and have vomiting or diarrhea as a result of radiation therapy. This will usually only occur if portions of the abdomen are irradiated.
When cancer of the oral or nasal cavity is treated with radiation therapy, a foul odor may develop as the tumor is destroyed by the radiation. This odor is usually temporary and decreases as the tumor dies.
If it is necessary to include an eye in the radiation field, a lack of tears may develop in that eye (dry eye) requiring artificial tear supplementation. Gradual loss of sight may occur in that eye.
What happens after the treatment is over?
It is important for your veterinarian to examine your pet periodically after radiation therapy is over. This will allow normal tissue side effects to be detected before they become advanced, and the effect of the radiation on the tumor to be evaluated. It is the goal of radiation therapy (with the exception of palliative treatment) to completely eradicate the cancer. In some pets this happens and no evidence of the tumor persists. In other pets the cancer or lump may never completely disappear, but growth is arrested and the tumor is essentially controlled. The specific results to be expected depend on many factors. Specific details on likelihood of success for a specific tumor will be provided to you by the cancer specialist.
Finally, it is important to realize that even though your pet may never be totally the same as before the cancer was diagnosed, it is possible in many pets to provide additional comfortable months or years of happy life through radiation therapy.
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