Radiation Oncology

Our team works closely with both the medical and surgical oncologists to evaluate every patient. We also collaborate with the many other clinical specialists at Penn Vet including internists, cardiologists, neurologists, and others as needed to keep your pet as healthy and happy as possible during, and after, their cancer care. This team approach ensures we consider all available treatment options, and allow you to make an informed decision.

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:

• 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
  • Lymphoma

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 is given in a series of treatments that encompass several weeks. This schedule helps protect normal tissue by spreading out the total dose of radiation. 

The treatment area is designed to include all of the cancer and as little normal tissue as possible.

The total dose used and the number of treatments depends on many factors, including:

• The size and location of the cancer (i.e. which normal tissues will be within the treatment area)
• The general health of your pet
• The type of cancer present

The most important consideration is the total amount of radiation that can be administered without compromising the ability of the patient’s healthy tissue to heal. The treatment area may be marked with ink to enable the treatment to be directed to the same area every time. Please maintain the marks as directed.

Definitive or Curative Intent radiation therapy is given in a series of small daily dose treatments that encompass several weeks. This type of radiation is chosen when there is potential for long term control. This schedule helps protect normal tissue by spreading out the total dose of radiation. Most patients receive treatments on a Monday-Friday schedule for a total of 16-21 treatments over a course of approximately one month (with some exceptions). Weekends are reserved as a rest period during which normal tissues have an opportunity to recover from the treatment. At times, your pet may need more extensive rest periods. 

Palliative radiation therapy is less intensive and is given in larger fractions of radiation 1-2 times a week for a total of 3-6 weeks. The intent of palliative radiation is to alleviate any pain or clinical signs, such as pressure, bleeding, or pain. Palliative radiation therapy is not considered a cure but is used to improve the patient’s quality of life. 

Veterinary patients are anesthetized for each dose of radiation to ensure they remain absolutely still during the treatment. Because of the anesthesia required, they should not be fed after 10:00pm the night before treatments, but water may be provided throughout the night. Pets may be sleepy for several hours following each treatment. 

The patient is monitored throughout the whole procedure. A wide selection of modern anesthesia drugs accommodates each patient’s individual requirements and provides a quick recovery. This allows radiation to be safely administered five days a week.

We rely heavily on owner feedback as to how your pet is doing. If for any reason you do not feel they are recovering well, please let us know and we will be happy to adjust the anesthetic protocol as best we can. Something unique to PennVet is our use of SVAP’s (subcutaneous venous access ports) to administer anesthesia.

Patients may stay in the hospital from Monday through Friday, or come in for each treatment. We do not offer boarding on weekends as we would like them to be home and with their families. 

Outpatient treatments take approximately two hours. The first day of treatment is typically the longest as we work to match the CT scan and make any necessary adjustments. The anesthesia protocol will also be determined at this point.

In the case of daily treatments we also place the SVAP as a minor surgical procedure. Please plan on the first treatment day being the longest.

Here at Penn Vet we like to spoil our patients with love, attention, and of course the occasional treats. If there are any dietary discretions please let us know and bring appropriate treats or food for them.

Subcutaneous Venous Access Port (SVAP)

Something unique to PennVet is our use of SVAPs (Subcutaneous vascular access ports). 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)

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The SVAP consists of a long, thin, soft, flexible tube that is placed into a large vein (usually in the neck), and an attached reservoir that sits in a pocket under the skin (typically around the shoulder blade area) where drugs can be given or blood samples withdrawn. Placement and removal of the SVAPs require a brief surgical procedure lasting about 45 minutes each. Typically, the SVAP will be placed during the first radiation treatment and removed at the last treatment. 

The SVAP requires minimal maintenance. The SVAP will take up roughly half the neck from the base of the ear to the tip of the shoulder, with accompanying clipped fur. There will be two small incisions, one over the jugular vein and one just adjacent to the port itself. These areas should be checked for redness, swelling and discharge, and you should discourage your pet from licking, chewing or rubbing at the sites. If stitches are present, remove in 7-10 days. If the SVAP will not be used for a period of time, you will need to have a brief visit at PennVet to have the catheter “flushed” and “locked” every 2-3 weeks in order to prevent a clot from blocking the tubing and making it unusable. During the course of treatment, this maintenance will be performed at each visit.

Most complications associated with SVAPs are mild and easily managed, and consist mainly of soreness and swelling around the incisions for a few days. There is a small chance of localized infection, which is treated with antibiotics, but may occasionally require removal of the SVAP. Serious complications are rare, and may include generalized infection and blood clots.

Vascular access ports have been used for over 20 years in the treatment of human cancer patients, and their use is increasing in veterinary medicine. Overall, the benefits of SVAPs outweigh the potential complications for most animals undergoing radiation therapy, and have become a standard procedure at Ryan Hospital.

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.

Equipment includes a Varian Silhouette 21iX with RapidArc.

IMRT is a state-of-the-art treatment technique using a computer-controlled linear accelerator (LinAc) to sculpt the radiation beam to the specific tumor shape while avoiding adjacent normal tissues.

• The LinAc gantry rotates 360 degrees around the patient, delivering radiation beams from many angles while always focusing on the tumor and minimizing dosign to surrounding normal tissue.
• A multileaf collimator (MLC) continuously changes the shape of the radiation beam to match the contours of the tumor at every angle. Allows for more precise customization.
• This technique allows us to deliver radiation more precisely than with conventional treatment, resulting in fewer side effects.
• We can now treat patients that previously could not be safely treated.
• On –Board imaging system for quicker more accurate verification of treatment fields.
• Administer both photon (x-ray) beam and electron beam radiation. This depends on tumor size, depth, and location. 
• Quicker scan times to minimize anesthesia time for your pet.