What is Radiation?

Radiation therapy is a method of treating cancer with x-rays or electrons. The effectiveness of radiation therapy varies depending on tumor size, patient species, cancer type, and tumor location. It is most effective at treating tumors that occur in one area (localized disease) rather than tumors that have spread to other parts of the body (systemic disease). There are various different types of radiation therapy. Stereotactic radiosurgery (SRS) consists of 1-3 treatment sessions delivered on consecutive days, while conventional radiation therapy is typically given every day for a period of three to four weeks. Each treatment requires a brief general anesthesia. Both normal and cancer cells are affected, but radiation treatment is designed to maximize tumor effect and minimize the effect on normal tissues. While normal cells can regenerate following radiation exposure, cancer cells cannot.

How does radiation therapy work?

As a beam of radiation collides with a cell, the genetic material (DNA) which controls cell growth is altered, thereby inhibiting the cell’s ability to grow and divide. Radiation therapy can damage DNA directly, or create charged particles (free radicals) within the cell that in turn damage the DNA. Since cancer cells do not have the ability to repair themselves, cell death occurs after irradiation.

What types of radiation therapy are offered at SEVO-Med?

  • Thanks to a new partnership with PetCure Oncology, SEVO-Med is proud to be one of just a handful of specialty practices around the country offering stereotactic radiosurgery (SRS) for pets. SRS is an advanced form of radiation therapy that has been a standard of care in human oncology for decades, but has just recently become available for pets. It is a noninvasive therapy that utilizes unprecedented precision to deliver maximum radiation dose directly to a tumor with minimal exposure to the surrounding healthy anatomy. The result is increased effectiveness and efficiency, offering a full course of treatment in just one-to-three sessions while optimizing the ability to achieve both long-term survival and increased quality of life. Additional benefits to the patient include a maximum of just four anesthetic events, minimal side effects, and decreased risk.
  • Conventionally Fractionated Radiation Therapy (CFRT) uses targeted radiation to shrink or destroy cancers, including those that cannot be safely or completely removed by surgery alone. While SRS involves a fewer number of high-dose treatments, CFRT consists of multiple lower-dose treatments spread out over a longer period of time. It can be utilized in conjunction with chemotherapy, following surgery, or as the sole treatment in cases where SRS is not an option. CFRT is typically administered daily in 15-20 treatment sessions over three-to-four weeks!
  • Palliative radiation therapy is intended to increase a pet’s comfort and quality of life, often when local tumor control is deemed unlikely. This option is especially useful when treatment options with the intent to cure, such as SRS or surgery, are not viable. Palliative treatments are typically delivered once per week over three-to-six weeks with the goal of relieving symptoms such as pain, bleeding and decreased mobility.
  • Unsealed source radiotherapy using soluble radioisotopes which are administered by injection or ingestion.
  • Contact therapy for superficial dermal lesions using the Strontium90 probe.
    All radiation therapy is delivered by highly-trained and licensed staff, including a board-certified veterinary radiation oncologist and a licensed radiation therapist with extensive training in human radiation oncology.

How has veterinary radiation oncology advanced in recent years?

As technology and medical capabilities have advanced in human medicine, those treatments and best practices are making their way to veterinary medicine as well. For example, while SRS has been a standard of care in human oncology for decades, it has only recently become available to pets. With the addition of PetCure Oncology in 2017 and an upgraded linear accelerator to administer treatment, SEVO-Med now has the ability to deliver SRS with RapidArc® technology and on-board imaging. Not only is this technology on par with the top human radiation therapy centers in the country, it also puts SEVO-Med among only a handful of veterinary centers in the country with such best-in-class capability.

To learn more about SRS or PetCure Oncology, watch this quick video:

When is radiation therapy indicated?

Radiation therapy is primarily used to target local disease, meaning tumors that have not spread to other parts of the body. Radiation therapy may be given therapeutically, where the treatment has a survival benefit with curative intent, or for its palliative effects when a cure is not probable. The aim of treatment is local disease control or pain relief. Whether indicated as a curative method or to relieve discomfort, radiation therapy has the potential to improve the quality and duration of the life of your pet.

Radiation therapy may be indicated as a primary treatment or in combination with surgery and/or chemotherapy depending on the stage and type of disease present.

What goes into the treatment planning process?

Prior to beginning any course of treatment, it is suggested that certain diagnostic tests are performed to ensure proper and most effective treatment planning. Before starting a treatment regimen, it is imperative to know the extent of disease and whether the disease has progressed to other areas of the body. This process, known as staging, allows us to treat your pet as an individual.

Diagnostics available at SEVO-Med include:

  • In-house blood work and cytological evaluation, radiographs, ultrasound, fine needle aspiration, tissue biopsy, CT scan, bone marrow biopsy, lymph node aspiration, and tumor marker testing. More extensive testing, if needed is available on a referral basis. These tests alone or in combination can help determine the most effective therapy for your pet. All diagnostics are done in a way that minimize any stress or discomfort to your pet.
  • Computed Tomography (CT) Scan – Computed tomography is a diagnostic tool that can be utilized in planning radiation treatment design. CT scan is an x-ray technique that produces images which visualize internal structures in cross section rather than the overlapping images typically produced by traditional x-rays exams. This cross-sectional view assists the radiation oncologist in planning the most precise and effect treatment possible.

For SRS patients, the CT scan is then loaded into advanced treatment-planning software that is used to create a 3D reconstruction of the pet’s internal anatomy. This helps the radiation oncologist visualize the tumor and nearby critical organs with exceptional precision and clarity, enabling a treatment plan that maximizes the radiation dose to the tumor while minimizing the dose to surrounding anatomy.

What happens during a radiation therapy treatment?

Radiation is an outpatient, noninvasive procedure usually having duration of between 10-45 minutes. When you arrive for treatment, a member of the SEVO team will come get your pet. Because of the radiation involved during treatment, you will not be allowed to accompany him/her. Your pet will be taken into the treatment room and placed under general anesthesia. This is necessary to prevent movement and accurately target the treatment area. Since the eyes do not blink during sedation, a lubricant may be applied to each eye to prevent dryness. For this reason, your pet may seem “teary eyed” when you see him/her after treatment. Small reference marks which denote the tumor volume will be drawn out on the skin to help guide daily treatment. Your pet will be positioned on the treatment couch of the linear accelerator using alignment lasers to the above mentioned reference marks. The treatment team will then deliver the radiation from outside the treatment vault using beams from one or more directions targeted at the tumor site. During the time treatment is being administered, your pet will be monitored with closed circuit TV and vital sign monitors. Once treatment is complete, your pet will be awakened from anesthesia. Approximately 15 minutes after your pet is fully awake, he/she will rejoin you in the waiting room and be allowed to return home. Your pet will not be radioactive at any time during or after the treatment. Don’t hesitate to ask to tour the facility at any time.

What are the risks and side effects associated with radiation therapy?

The nature, severity and longevity of side effects associated with treatment depend on a number of variables including the treatment course, the location of the tumor, and the organs involved in the treatment field. Fortunately, less than half of veterinary patients undergoing radiation will experience adverse side effects. Some of the most common side effects seen are skin reactions, gastrointestinal upset and hair loss.

There are two types of side effects: acute and chronic. Acute or short-term side effects occur during treatment and are usually completely gone within a few weeks after completion of therapy. Chronic or long-term side effects may take months or years to develop after treatment is completed and are usually permanent. Occasionally, they are life threatening. Your radiation oncologist will detail particular side effects that might be detrimental to your pet.


Side effects can be managed with medication and supportive care, and are generally kept to a minimum. Remember that our major objective is to provide control of the malignancy while preserving a good quality of life for your pet. The benefits of therapy should outweigh the potential risks.

There is always an inherent risk associated with anesthesia. To minimize this risk, please do not feed your pet after midnight the night before each treatment. Free choice water is okay.

Will my pet’s diet differ while undergoing radiation therapy?

Overall, diet shall remain the same while your pet is undergoing radiation therapy. Due to the necessity for anesthesia it is VERY IMPORTANT THAT YOUR PET NOT HAVE ANYTHING TO EAT AFTER MIDNIGHT PRIOR TO THE DAY OF TREATMENT. Free choice water is okay. This is one of the most important things that you, as a pet owner, must adhere to. Otherwise your pet may aspirate (choke) on undigested food while under anesthesia. This can result in your pet developing pneumonia, which can be a life-threatening illness. If you make a mistake and your pet has had something to eat, please be honest and let the radiation therapist know. We share your concern for your pet and want to do what is best.

Am I allowed to regularly groom my pet?

It is important to speak with either the oncologist or radiation therapist before taking your pet to be groomed while under treatment. There may be some treatment areas that should not be exposed to soaps, perfumes, and other grooming chemicals. You may also notice that there are reference marks denoting the treatment area drawn out on your pet’s skin. These marks are very important and could easily be removed by bathing or shaving the treatment area. Please be extremely careful in helping to preserve these markings.

What happens if I miss an appointment?

It is very important to come to radiation therapy appointments as prescribed. However, missing a treatment will not affect your pet’s ability to benefit from radiation therapy. If a treatment is missed, it will be made up at the end of the treatment schedule so that your pet will receive the total number of fractions prescribed.

What if I have questions regarding my pet’s treatment?

While your pet is undergoing treatment, you will meet with the radiation therapist daily and the radiation oncologist at least once weekly, depending on how often you are scheduled for treatment. You may ask any questions or concerns that you have at these appointment times. We are also available anytime by phone and after hours for emergencies. Do not ever hesitate to call if you have questions or concerns, especially regarding changes in behavior, appetite, side effects, etc.

What does follow up care consist of?

Once your pet has completed the treatment regimen, the oncologist will want to see you return for a follow up appointment and routine check-ups. Follow up appointments will be arranged on your last day of treatment. Most patients are asked to come back for a recheck two weeks after radiation completion. SEVO-Med will continue to monitor the progress of your pet long term on an as needed basis. Again, if you have any questions or concerns after completing treatment you are always more than welcome to call and speak with the doctor or make an appointment to be seen.