Radiation Therapy Information

How Does Radiation Therapy Work?

Radiation destroys the ability of cells to divide, which is a process that is necessary for tumors to continue to grow. Both normal cells and cancer cells are affected, but the radiation treatment is designed to destroy tumor cells while minimizing the effects on the surrounding normal tissues. First, the radiation is administered over a series of treatments rather than a single treatment to allow the normal tissues to recover between treatments. Also, radiation therapy limits the damage to normal tissue because it is targeted to the local area in which the tumor is located.

What are the Benefits of Radiation Therapy?

Radiation therapy, alone or in combination with surgical excision, is used to shrink or destroy cancers that cannot be safely or completely removed by surgery alone, or cancers that are unaffected by chemotherapy. In some instances, permanent control of the tumor is possible through use of radiation therapy. 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. When used in combination with surgical excision, radiation therapy kills microscopic tumor cells in the surrounding area that would otherwise result in regrowth of the tumor. Radiation therapy may also be used in combination with chemotherapy when the tumor is likely to spread throughout the body.

Are There Risks Involved?

There are some risks involved with any type of treatment of cancer. Some normal cells will be killed by the radiation in addition to cancer cells. Some side effects (see section "What Are The Effects of Treatment") may occur as a result of these normal cells being killed. Usually these side effects are 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 withstand this portion of the treatment very well. Also, a thorough evaluation and diagnostic testing can help identify any potential problems prior to anesthesia.

How Is Therapy Given?

In radiation therapy, a machine directs high-energy radiation to the cancer and some normal tissue around it. Each treatment takes approximately 5-20 minutes. When treatments are given daily, the pet can either be hospitalized during treatment and can be able to go home for the weekends during treatment, get dropped off daily for treatment or be treated on an outpatient basis. If a pet is being treated once or twice a week, it will be admitted the morning of treatment and discharged the same day unless the pet's medical condition indicates otherwise.

Your pet has been, or will be examined by one or more cancer specialists. These specialists will determine whether radiation therapy will be useful for treatment of your pet's cancer. If radiation therapy is given to your pet, a Radiation Oncologist will plan the treatment specifically for your pet. Treatment for each patient is different. The Radiation Oncologist will also supervise treatments throughout the course of radiation. After the first radiation therapy treatment, veterinary technicians will deliver most treatments. These individuals have had special training and experience in the administration of radiation for cancer treatment.

Is Radiation Therapy Expensive?

Treatment of cancer with radiation can be costly. It involves very complex equipment as well as the expertise of many health care professionals. The exact cost of radiation therapy varies with the type and number of treatments required. Your veterinarian will give you an estimate of the cost.

How Long Does the Treatment Take?

Radiation therapy is usually given in a series of 15-20 daily treatments which encompass approximately three to four weeks, although some treatment protocols are only one to six treatments. This schedule helps protect normal healthy tissue by spreading out the total dose of radiation. The total dose used and the number of treatments in which the total dose is given depend on many factors including the size and location of the cancer, the general health of your pet and the type of cancer present.

What are the Effects of Treatment?

In general, the side effects of radiation therapy are mild. During treatment the Radiation Oncologist 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. 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 inadvisable for you to purchase over-the-counter drugs and treat these conditions yourself unless instructed to do so by your veterinarian. This skin moistness will usually subside 7-14 days following the completion of radiation therapy.

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 four to six months, but hair regrowth occurs in most patients. The color of the regrowing hair and skin in the treated area are likely to change permanently.

It is unusual for animals to become nauseated or have vomiting and diarrhea as a result of radiation therapy. This will usually only occur if portions of the abdomen are irradiated. Weight loss does occur in pets undergoing radiation therapy. Pets receiving radiation therapy skip breakfast the morning of treatment and often are not ready to eat again until late afternoon and this typically results in a reduction in body weight. After radiation therapy is completed, the weight is typically regained.

When cancer of the oral and nasal cavity is treated with radiation therapy, a foul odor may develop as side effects occur in these areas and/or the tumor is destroyed by the radiation. This odor is usually temporary and decreases over time. If the eyes are included in the treatment field, the development of cataracts is possible and your veterinarian will discuss this with you prior to treatment.

This describes the general side effects anticipated during radiation therapy, but the severity varies from patient to patient. Your veterinarian will discuss any special issues related to your pet's prescribed radiation treatments.

What Happens After Treatment?

It is important for your veterinarian to examine your pet periodically after radiation therapy is completed. 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 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. The cancer specialist will provide specific details on the likelihood of success as part of the evaluation process.

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 to provide him/her many additional comfortable months or years of happy life through radiation therapy.

What Happens If My Pet Has an Emergency?

If you think your pet is seriously ill and needs immediate medical attention, you should come directly to The Animal Medical Center. A doctor is on duty 24 hours a day, 365 days a year. You will be seen by the emergency doctor in the second floor clinic, who will determine if hospitalization is necessary. If it is a day when the Oncology Service is in the hospital, the case will be admitted directly to Oncology. On other days another service will manage the case until the Oncology Service is on duty.

If you are not sure if you have an emergency, you may choose to call (212) 329-8740. This is the Oncology Service telephone number. A doctor will answer if one is available. A doctor on the Oncology Service is in the hospital seven days a week to care for hospitalized patients.

Radiation Therapy Staff

The radiation oncologist at the Animal Medical Center is Dr. Rachel St-Vincent. Prior to starting radiation therapy you will meet with her or with one of the Medical Oncologists to discuss the benefits and side effects of radiation therapy for your pet. Dr. St-Vincent oversees treatment of all pets going through radiation therapy.

Various technicians are specifically trained in radiation therapy treatments. They may call you with periodic updates and you may also call and speak to them about the status of your pet. Call (212) 329-8753 which is the direct number for radiation therapy.

If your pet is not a patient at the AMC, please call 212-838-8100 to set up an appointment.