There are many misconceptions around radiation treatment. Many dog owners feel that radiation therapy involves a pill or is a treatment that will send toxins throughout the body making their dog feel ill.
The truth is that this description of radiation could not be further from reality. It's important to understand radiation therapy, not only because it's an excellent treatment option for many types of cancer in dogs, but also because it's a common medical treatment that you or a loved one might undergo in the future.
This article will discuss the basics of veterinary radiation oncology including who performs radiation, what radiation therapy is, common indications, types of radiation therapy, and possible side effects.
Who Performs Radiation Therapy?
Radiation oncologists determine the best radiation protocols for your dog and oversee all radiation treatments. Typically, a medical oncologist will refer you to a radiation oncologist if they feel that radiation would be helpful for your dog.
Radiation oncology is its own specialty in veterinary oncology. These individuals have completed four years of veterinary school, a one-year internship, then a two or three-year radiation oncology residency at one of 14 veterinary institutions throughout the US. They have also passed rigorous board exams and published original research in their field.
A radiation oncologist has advanced training in physics, radiology, and oncology.
This group of specialists is different than medical oncologists (like me); medical oncologists typically perform the initial workup on a patient that has cancer, decide which cancer treatments are appropriate, and give chemotherapy.
What is Radiation Therapy & How Does It Work?
Radiation treatments are administered under the care and guidance of a radiation oncology team and radiation oncologist.
A linear accelerator is the type of machine needed to administer radiation treatments (see image below). These machines are quite expensive, so not every veterinary specialty clinic will have one. Every veterinary teaching school should have a radiation oncology department, however.
For each treatment, the patient lays on the "couch", which is the flat horizontal section, and is placed under anesthesia for a short period of time.
Anesthesia is essential when treating a dog with radiation. It ensures that the patient lays completely still during the treatment so that the exact same location (the tumor) is treated each time.
For certain areas of the body such as the head and nose, the radiation oncologist will create a custom mold for your dog that fits over the treatment area, for even better accuracy in positioning (see below).
Once the radiation plan is created based off of the CT scan, the linear accelerator will be programmed with the patient's data. The final plan will look similar to the one below in which a nasal tumor is being treated. The red sections are the areas receiving the most radiation (the tumor), while the yellow and green areas are receiving far less (those are normal tissues). The gray areas are not receiving any radiation.
In veterinary oncology, we typically treat with photons (a unit of energy). In the most basic sense, this type of radiation primarily kills cells by damaging DNA inside the cells, which eventually leads to cell death.
It's important to understand that radiation is very targeted. We're only treating the tumor, and only the treated tissue is absorbing photons.
What is a Radiation Consultation like?
The first time you meet with a radiation oncologist, you will be scheduled for a 1 hour consultation. During that visit you will discuss which radiation protocol the radiation oncologist feels is best (as well as others that might also help), the cost of treatment, the number of treatments needed, as well as possible side effects. The radiation oncologist will also tell you how well they feel radiation will work for your dog's tumor (will it help control the tumor for 6 months, 1 year, 3 years, etc.).
Before radiation can begin, a radiation-planning CT scan is typically indicated. If all other testing has been completed for your dog (chest x-rays, ultrasound, etc.), sometimes this can be done on the same day as your consultation.
In order for a CT scan to happen on the day of your consult (logistically-speaking), you usually have to (1) fast your dog (ie. don't feed breakfast) (2) request a morning consultation (3) request a same-day CT in advance so the radiation group can plan ahead of time.
Once the CT is performed, it's typically sent to a physicist and the radiation plan is created. The plan ensures that the majority of radiation dose is concentrated on the tumor and that the surrounding tissues receive very little to no radiation. Typically the plans are so precise that tissues only millimeters away from the tumor are receiving ZERO radiation (especially with stereotactic radiation therapy).
Creating the radiation plan typically takes at least a few days. The radiation oncology team will usually schedule your dog to begin radiation the week after your CT scan.
Types of Radiation Protocols
For the purposes of this article, we'll talk about three basic types of radiation therapy: palliative, definitive, and stereotactic.
Palliative Radiation Therapy
Palliative radiation therapy involves treating a tumor with (typically) four or five radiation treatments and then stopping. The protocol is different for different tumors and might be different depending on the preference of the radiation oncologist. Sometimes treatments are given Monday - Friday, other times once per week, other times twice per week. The protocols vary.
Palliative radiation is often used to decrease pain and increase quality of life. For dogs that have osteosarcoma (bone cancer), it can do a much better job of decreasing pain than oral pain meds; the effects typically last for a few months; treatment can be repeated a second time as well. For dogs that have oral melanoma (which often invades the jaw), this type of protocol can both relieve bone pain and kill tumor cells. Tumor control is often seen for a few months to 6 or 8, depending on the case.
Palliative radiation therapy can also be used in conjunction with chemotherapy to help treat tumors that are too large for surgery such as large mast cell tumors or hemangiosarcoma of the skin.
Since palliative radiation only involves a few treatments, we should see minimal to no side effects. Sometimes there can be mild redness, irritation or inflammation to the tissues that are treated (especially if the mouth is being treated), but the side effects are not expected to be significant.
Definitive Radiation Therapy
Definitive Radiation is probably what most people think of when they think of radiation. This type of protocol is most commonly used when a tumor (such as a mast cell tumor or soft tissue sarcoma) is removed, but cells are left behind after surgery. If a second surgery cannot be performed to achieve a "complete excision", radiation is an option to prevent the tumor from recurring.
Definitive radiation typically involves giving small daily doses of radiation to the treatment field. The treatment field is typically a surgical scar plus 2-3 cm of tissue surrounding the scar (anywhere we think there still might be cancer cells). The treatments are administered on a Monday to Friday basis (5 days per week) for about three and a half weeks (18 or 19 treatments).
Each treatment is administered under a brief period of anesthesia (sometimes only 20 minutes) and the patient can go home the same day. If it's too difficult for the family to drop their dog off and pick them up every day for treatment, they can either leave them for the duration of treatment or take them home for weekends. This is up to the family to decide.
Typically skin side effects begin to develop towards the end of week two of treatment and last for a couple of weeks after treatment finishes. The skin typically becomes red, inflamed and may look ulcerated. The patient will definitely need to wear an e-collar if the treatment area is located in a region where they might lick it - the tissues are sensitive and need to be protected from their tongue.
The hair is usually lost during treatment but often returns. One odd thing is that the hair that grows back is always white, regardless of the color that was there initially.
Definitive radiation works very well for incompletely removed tumors. It can also be used for nasal tumors and certain types of internal tumors as well.
Stereotactic Radiation Therapy
Stereotactic radiation is also known as SRT and SRS; Cyberknife is a form of this therapy. This is the most advanced form of radiation therapy available in veterinary oncology.
Not every linear accelerator is able to perform SRT.
The beauty of SRT is it's precision. We are able to treat tumors with significantly larger doses of radiation per treatment, because the machine is so good at accurately treating the tumor and safely sparing surrounding tissues.
This means that most stereotactic protocols involve just three treatments (sometimes just a single treatment). These treatments are given on consecutive days, so treatment is finished in just three days.
There are typically minimal side effects associated with SRT. Some patients experience mild redness, inflammation or scabbing in the treatment area.
Currently we are using SRT most commonly for brain tumors, osteosarcoma (it relieves pain AND kills tumor cells in bone), nasal tumors, many types of non-resectable tumors, and more.
Many dogs that receive SRT for nasal carcinoma have control of their tumor for 1 year or more. Dogs with osteosarcoma that receive SRT and chemotherapy can also live a year. Dogs that receive SRT for certain types of brain tumors are expected to live more than two years.
Since SRT is relatively new for veterinary oncology, we are regularly learning of more uses for this treatment modality. If your vet feels "stuck" and isn't sure about whether any treatment options exist for you dog's tumor, it's worth calling up the nearest radiation oncologist to see if they think he might be a candidate for SRT.
Does Pet Insurance Cover Radiation Therapy?
If you have a good comprehensive pet insurance plan, radiation therapy is typically covered. If you are paying out of pocket, the cost varies widely depending on your location in the US/Canada and the type of radiation treatment your dog is receiving.
Palliative/Coarse fractionated protocols are the least expensive (very rough ballpark $3500-$5000), definitive protocols are more expensive (very rough ballpark $5500-$13,000), and stereotactic protocols are typically the most expensive (rough ballpark $7500-$13,000).
Sometimes clinical trials can supplement the cost of treatment; these may be found in both private practice and academic settings.
How To Find A Radiation Oncologist
The link below will help you locate the nearest radiation oncologist. Be certain to check the box "radiation oncologist" next to "specialty" (otherwise it will also search for radiologists, which won't be helpful).
Click here to find a radiation oncologist near you
If you can't find a local radiation oncologist, reach out to your primary care provider or local specialty clinic for more information.
Dr. Lori Cesario
Board Certified Veterinary Oncologist
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