Radiation Oncology

There are many tumor types, both malignant and benign, that can be treated using radiation therapy. Treatment recommendations and outcome will depend on tumor behavior, prognosis, and the patients’ medical history, among other factors.

Tumors frequently treated with Radiation Therapy include but are not limited to:

• Lymphoma
• Tumors of the skin / soft tissue often on the limbs and body:
• Soft tissue sarcoma, mast cell tumor, carcinoma, melanoma, fibrosarcoma, hemangiopericytoma, etc
• Bone tumors of the limbs, skull, spine, pelvis:
• Osteosarcoma, chondrosarcoma
• Oral and Nasal tumors:
• Melanoma, odontogenic tumors, squamous cell carcinoma, etc.
• Tumors of larynx, pharynx, trachea
• Thyroid tumors
• Lymphoma
• Tumors of the Brain or Spinal Cord
• Periocular, Facial, and Ear Tumors
• Anal/Rectal tumors (Anal Sac Adenocarcinoma)
• Bladder, Prostate, Ureteral/Urethral tumors (Transitional Cell Carcinoma, etc)
• Heart Based and Mediastinal tumors
• Thymoma
• Chemodectoma

Treatment planning can be performed on the same day in cases of a simple set up, but more than likely will require a CT scan—which we will schedule the same day or within the next few days. Your pet will be required to be fasted for this procedure as they will need to be under anesthesia.

During the CT scan your pet will be positioned the same way they would for treatment, this may include a custom mold, positioning bag, etc.

Once the imaging is complete, the images are sent to a planning computer where the Radiation Oncologist will create a plan. Planning with the use of a CT helps to determine the exact extent of the tumor growth, and the involvement of surrounding structures.

Complex plans can now be implemented to allow the Radiation Oncologist to identify the optimal treatment, targeting the cancer with as little effect as possible on surrounding normal tissues. This process can take some time, and we usually schedule the treatment start date about one week post CT scan.

Radiation therapy for involves a series of treatments over several weeks to protect normal tissue by spreading out the total dose. The treatment area is carefully planned to include all of the cancer and as little normal tissue as possible. The total dose and number of treatments depend on factors like the size and location of the cancer, the pet’s general health, and the type of cancer.

There are two main types of radiation therapy:

1. Definitive or Curative Intent Radiation Therapy: Given in small daily doses over several weeks. This aims for long-term control and includes rest periods on weekends.
2. Palliative Radiation Therapy: Less intensive, given in larger doses 1-2 times a week for 3-6 weeks. This aims to alleviate pain and improve quality of life, not to cure.

Pets are anesthetized for each treatment to ensure they remain still. They should not eat after 10:00 PM the night before treatments, but can have water. Pets may be sleepy for several hours post-treatment. The anesthesia protocol is tailored to each pet, and owner feedback is important for adjustments.

Ryan Hospital uses Subcutaneous Venous Access Ports (SVAPs) They are long-term, surgically placed intravenous catheters that reduce the time, trauma, and discomfort associated with the placement of multiple short term catheters.

Vein access is necessary to ensure the patient’s safety during the multiple anesthesias required for animals undergoing radiation therapy. In many animals, it is difficult to maintain this access throughout the course of therapy with multiple short term catheters because blood vessels can become scarred, collapsed, and inflamed when they are repeatedly used. SVAPs not only ensure a simple, non-stressful method to gain venous access, but they also minimize the need to use multiple veins, thereby preserving these vessels)

During treatment the oncologist will monitor the effect of the radiation on the cancer as well as on normal tissue.

Most side effects that occur during radiation therapy, although unpleasant, are usually not serious, and are almost always limited to the area being treated. Side effects will depend on the type and dose of radiation as well as location being treated.

Many animals develop skin changes in the area being treated, such as a redness of the skin near the end of, or after, radiation therapy. This may progress to a dry or moist skin reaction, which resembles a severe sunburn or blistering rash. This “radiation dermatitis” may cause your pet to rub or scratch, but it is important you try to keep your pet from doing this. Your veterinarian may prescribe medication and/or physical means to prevent rubbing and scratching.

Hair loss in the treated area is common and may persist for some time, but regrowth occurs in many patients. The color of the regrowing hair and skin in the treated area are likely to change.

It is unusual for animals to become nauseated and have vomiting/diarrhea as a result of radiation therapy. This will usually only occur if large portions of the abdomen are irradiated. 

Side effects involving other tissues that may be within the radiation treatment area (such as the eye, mucous membranes, and bone) will be discussed with you on an individual basis.

The time from first appearance of acute side effects (i.e. those that happen in the immediate treatment period) until their resolution is usually 3-4 weeks. Chronic side effects, when they occur, develop gradually over months to years. 

This includes fibrosis (scar tissue formation) and decreased ability to heal a wound or bone fracture. There is also a very small risk of a secondary cancer within the radiation site many years after treatment is administered.

At the end of your pet’s course of radiation, we like to have a little party. Our patients get lots of attention and treats, as well as a photo.

After your pet’s graduation, it is important for your veterinarian to examine your pet periodically. This allows side effects to the normal tissue as well of the effect of the radiation to the tumor to be evaluated.

Your pet will also require follow up appointments to check on any side effects until they are fully healed. We like to see them back in about two weeks following completion of radiation, after which we will gradually start spreading out re-check appointments to monitor tumor response as well as any regression or progression of the cancer itself.

Any other follow up care will be discussed on a case to case basis. 

Your pet is now a part of our family. You can always call or email with any questions or concerns you may have and we are always happy to help.