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Radiation Therapy

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The idea of treating your beloved pet with radiation therapy can sound daunting. However, new studies and findings have discovered that using radiation therapy for treating cancer in our canine and feline companions can actually make a significant difference in overall survival and quality of life. Typically, radiation therapy is used in dogs and cats after surgery, or in conjunction with chemotherapy, immunotherapy, and targeted therapies. In certain tumors, the goal of using radiation therapy is to eliminate any cancer cells that may remain following surgery. However, depending on the type of cancer and if it is localized to a certain area, Dr. Ratterree, a veterinary radiation oncologist, may recommend the use of radiation therapy alone. Radiation therapy can even be used to ease the pain of certain cancers in pets such as bone tumors (osteosarcoma). This form of therapy is called palliative (or coarse fractionated) radiation therapy, and it can be delivered any location of cancer from 2 – 6 doses with minimal to no acute side effects to normal tissue.

In veterinary medicine, radiation therapy is most commonly delivered with a sophisticated machine called a linear accelerator (external beam radiation). This machine delivers ionizing radiation to the malignant cells to inhibit their ability to divide and grow. Both normal and cancer cells are affected, but the radiation treatment is designed to maximize tumor effect and minimize normal cell effect. Definitive radiation therapy is given in a series of treatments (called fractions) administered on consecutive weekdays. This schedule helps protect normal, healthy tissue by spreading out the total dose of radiation over some time. The total dose used and the number of fractions in which the total dose is administered depends on many factors and may be different for individual patients. These factors include the size and location of cancer, the general health of your pet, and the type of cancer present. On the first day of radiation therapy, Dr. Ratterree and the radiation therapists work together to ensure that your pet’s treatment is delivered precisely as planned. Typically, treatments are done on weekdays (unless an emergency), patients are allowed to go home the same day, and the average actual treatment time takes approximately 15 – 30 minutes.

Radiation therapy can have side effects in animals just as it does on human patients. The side effects of radiation usually appear halfway through the prescribed dose and can last from 1 – 3 weeks, depending on the site that is being treated. There are many topical and oral medications that Dr. Ratterree can prescribe to help minimize or prevent any impact that radiation therapy has on your pet’s quality of life. As expected, hair loss at the irradiated site is most common. Other side effects are very dependent on the particular site that is being treated. Your Fetch oncologist can discuss the potential side effects of radiation therapy that may be expected in your pet at the initial consultation or any time during the course of therapy. We are here to answer any questions that you may have in regards to your pet’s care – just ask!


Our Radiation Therapy Services


Fetch Specialty & Cancer Veterinary Centers not only uses external beam radiation to treat our cancer patients but we can also use a very localized form of radiation called Plesiotherapy (the prefix plesio– is Greek for close or near). A strontium 90 applicator is a sealed source emitter that entails placement of a sealed radiation source in contact with the skin surface. The highest dose of radiation is deposited at the skin surface and the dose drops off rapidly with increased tissue depth (approximately 5% of the dose reaching deeper than 4 mm into the tissue). A single large bolus dose of radiation may be administered by direct application of the strontium 90 applicators to a superficially located tumor with minimal risk to underlying healthy tissues. One application field is used for small tumors, and several overlapping fields are used for lesions that exceed the width of the radiation source. The dose of radiation delivered depends on the interval of time during which the applicator is in contact with the skin. Strontium 90 irradiation has been used successfully to treat small superficial lesions (such as squamous cell carcinoma, mast cell tumors, melanoma) in dogs and cats. By having multiple forms of radiation therapy, we can offer multimodality treatment plans for our canine and feline patients.

Stereotactic Radiotherapy
Stereotactic radiotherapy (SRT) is a type of radiation therapy that uses high-powered forms of energy on a focused area of the body. Despite its name, SRT is not actually a surgical procedure and is most often used to treat tumors that cannot be surgically removed. Originally used for nonsurgical brain tumors in humans, SRT can now be used for a wider variety of tumors such as nasal and bone tumors.

Stereotactic radiotherapy is an advanced form of radiation therapy, delivering high doses of radiation in a short period of time, destroying the tumor without harming the healthy tissue surrounding it. This aggressive approach results in more rapid tumor shrinkage, faster tumor-induced pain relief, and very often provide longer disease control to larger tumors. It even has the potential to result in a cure. The entire procedure is noninvasive, so your pet will experience little to no discomfort and the risks associated with treatment are minor.

Until recently, pet owners had very little access to stereotactic radiotherapy. Fetch is proud to offer the most advanced and up to date treatments for our companion animals. Dr. William Ratterree, Board Certified in both Medical and Radiation Oncology, has gone through extensive training to offer on-site, high-quality radiation treatments. We are the only oncology center located in Bonita Springs that offers both IMRT and SRT with an on-site radiation oncologist. Schedule your appointment today to see what treatment options are best for your pet.

Targeted Therapy
The aim of targeted therapy is to attack a certain target on cancer cells while doing less damage to the normal cells in the body. Targeted drugs can be used as the primary treatment for some cancers, but are more often used in combination with surgery, radiation therapy and standard chemotherapy. Unfortunately, not every type of cancer can be helped by targeted therapy.

There are many different types of targeted therapies available to treat people with a variety of cancers and are considered the gold standard of treatment for certain cancers (such as the use of Gleevec® for Chronic Myelogenous Leukemia or CML). There are a few options available for our companion animals. The two main groups of these therapies include monoclonal antibodies (see Immunotherapy section) and small molecule inhibitors, such as Palladia.

Palladia® (toceranib phosphate) is FDA-approved for dogs with grade II or III recurrent cutaneous mast cell cancer with or without regional lymph node involvement. Palladia is a multiple tyrosine kinase inhibitors, having both direct antitumor and anti-angiogenic activity. Palladia is also used off-label to treat a variety of other tumors in both dogs and cats, although the efficacy of this drug against other cancers has not been clearly defined. Palladia is generally well tolerated but can cause side effects such as loss of appetite, nausea/vomiting, diarrhea, low white blood cell counts and protein loss through the kidneys. Palladia can be used as a single agent in a treatment protocol, but it can also be combined with radiation therapy and standard chemotherapy. To see if Palladia is a treatment option for your pet, ask your oncologist.