Radiation Therapy

Southwest Veterinary Oncology, ArizonaRadiation therapy is effective for control of certain types of cancer. It may be used alone or in combination with other forms of treatment. Radiation therapy is indicated for the treatment of tumors that would have unacceptable functional and/or cosmetic side effects if they were surgically removed.

It can also be used to eliminate residual disease left behind when surgery could not remove the entire tumor without creating serious side effects. All of the side effects associated with radiation therapy will be limited only to the area where the radiation is applied. “Radiation sickness”, manifested by nausea, vomiting, and diarrhea, is not seen in veterinary patients.

Radiation therapy cannot be given in a single large dose sufficient to control tumors without causing severe complications. Giving small doses over a period of time gives the best chance of controlling the tumor with minimal damage to surrounding normal tissues. Radiation therapy is usually given in 12 or more small doses of radiation over a 3-4 week period.

Our radiation unit is a 6 meV linear accelerator with surface electron capability. Each treatment requires 10-30 minutes. The patient must remain perfectly still during the treatment so that the radiation only goes where it is needed. A short-acting anesthetic is given to immobilize the patients. There is a small but definite risk associated with repeated anesthesia; therefore, patients are monitored closely.

Many factors affect whether or not a tumor will respond to radiation therapy. Larger tumors require larger doses than smaller ones. The anatomical location may mandate that sensitive normal tissues, such as the eye, be included in the treatment field.

The type of tumor is also important as well as the type of radiation therapy used. The effects of the radiation therapy are not instantaneous. Most tumors will not have any visible changes for several weeks. Some will not change in size, but stop growing. The most important thing to remember is that while the side effects will be manageable and transient, tumor control should be permanent. Your veterinarian will work closely with you to keep your animal comfortable and healthy during radiation therapy.

The quality of time you spend with your pet is always the first priority.


Chemotherapy is used in many disease processes. It is indicated in diseases known to be sensitive to chemotherapy (lymphoma, multiple myeloma), to treat systemic diseases (metastatic cancers which can spread to many organ systems), to treat microscopic diseases which we cannot see or feel at the present time, and to sensitize tissues for radiation therapy to be more effective. Some diseases in which chemotherapy may be indicated include lymphoma, mast cell tumors, osteosarcoma, soft tissue sarcomas, and hemangiosarcoma

Our main goal with chemotherapy is to provide an excellent quality of life, to control cancer and its spread (metastasis), and to prolong survival of our patients.

The majority of our patients tolerate chemotherapy extremely well. This is important to understand because a notion exists that animals will have the same degree of side effects as people undergoing treatment. Again, we want to treat the cancer while maintaining the best quality of life. Side effects, which are managed by the pet’s owners the majority of the time, can include a few episodes of vomiting, diarrhea, decreased appetite, or none of these.

We see your pet for specific rechecks. A complete blood count is always performed prior to administering chemotherapy in order to evaluate whether the patient has enough white blood cells to be treated. General treatment times for the majority of our patients are usually 1.5-2 hours.


Our own immune system plays an incredibly large role in cancer development, spread, and even remission. Because of this, we strive to use our own body’s immune system to attack and kill cancer cells by this unique ‘Tumor-Host’ relationship. Immunotherapy involves the use of substances (natural or modified) or methods that change this specific tumor-host relationship in order to use the patient’s own body to have direct effects on the tumor or change the tumor microenvironment.

Immunotherapy has many approaches in its use and application. This includes nonspecific and specific immunomodulation, growth regulators, genetic modifications, and antibody therapy. Immunotherapy has long been used in people. Some examples include the use of genetic therapy or modification, monoclonal antibodies, tumor antigen vaccines, and retinoids.


Melanoma Vaccine

Canine melanoma is an aggressive form of cancer that typically appears in a dog’s mouth, but also may appear in the nail bed, foot pad, or other areas. The vaccine is indicated for the treatment of dogs with stage II or stage III oral melanoma for which local disease control has been achieved (negative local lymph nodes or positive lymph nodes that were surgically removed or irradiated).

This is the first time that the U.S. government has approved a therapeutic vaccine for the treatment of cancer – in either animals or humans. Unlike classic vaccines for infectious diseases, this vaccine is intended to treat rather than prevent disease.

After staging of the melanoma, and ideally after therapy to achieve local control, the vaccine is administered once every two weeks for four treatments, and then every six months thereafter. The vaccine will be administered via new Canine Transdermal Device, which delivers the vaccine without the use of a needle. Repeat testing (including complete blood count, chemistry panel, and thoracic radiographs) is typically recommended periodically throughout vaccine therapy.

Radioactive Iodine

camera for detecting cancer with gamma raysRadioactive iodine (RAI) has become the treatment of choice for treating feline hyperthyroidism because of the single dose regimen and lack of side effects. RAI treatment is based on the fact that the thyroid gland is the only tissue in the body that actively accumulates iodine, which it uses to produce thyroid hormones.

Radioactive iodine is rapidly absorbed by the hyperfunctioning thyroid tissue. The RAI emits a beta particle which selectively destroys the tumor while leaving normal tissue undamaged. Thyroid function typically returns to normal in 1-3 months.

Before treatment with RAI, a thyroid scan is performed using a low energy radioisotope (technetium pertechnetate). The scan will confirm the diagnosis, identify the number of abnormal thyroid lobes, and aid in determining the optimum radioactive dose required for effective treatment.

The majority of cats (90%) need to be treated only once. Most cats are hospitalized from 4-7 days, depending on the dose of RAI administered and the excretion rate of the iodine. Once admitted, your cat cannot be discharged until his/her radiation exposure rate is at the legal, safe limit. No visitation is allowed because of the radiation safety regulations. Cats are required to be up-to date-on vaccinations for upper respiratory viruses.


Cryotherapy is the use of cold temperatures to kill cells. Liquid nitrogen and nitrous oxide are the most common agents used to perform cryotherapy. The cold temperature creates an ‘ice ball’ which is then capable of destroying cancer cells in the immediate area of the cryotherapy probe. Because it uses a superficial probe, this treatment is best suited for small, superficial tumors. It is commonly used on areas such as the skin, eyelids, oral cavity, and peri-anal region.


Surgery is the mainstay of treatment for many pets with cancer. Depending on the type of cancer, surgery alone may affect long term control or “cure,” or may be recommended to “debulk” a tumor prior to other treatment such as radiation or chemotherapy. If surgery is indicated for your pet, we will refer you to our board-certified surgeons.