Radiation Therapy In Pets: Types, Administration, and Side Effects
Sun, April 18, 2021

Radiation Therapy In Pets: Types, Administration, and Side Effects


Radiation therapy involves the use of ionizing radiation to destroy the DNA of cancer cells, explained non-for-profit teaching hospital University of Minnesota: Veterinary Medical Center and VCA, an operator of over 1,000 animal hospitals in the US and Canada. Since cancer cells grow and divide faster than most normal cells, radiation therapy interferes with the cancer cell’s ability to replicate and can shrink a tumor or eliminate it. Radiation is also used for diagnosis and for therapeutic purposes. For example, low doses of radiation is used to take x-rays.

How Is Stereotactic Radiation Therapy Used in Veterinary Medicine? (2019)

The respondents were located in the US (88%), Canada (3%), Europe (8%), and Australia/Asia Pacific (2%), according to Elizabeth M. Dunfield and colleagues of biomedical and life sciences journal PMC. The participants categorized their veterinary facilities as private practices (51%), academic (university-based) (46%) or both (3%). 85% held board certification in Radiation Oncology, with the remaining respondents having DVMs without board certification (14%) and a board certification in Diagnostic Imaging (2%).

The common types of radiation therapy provided by Stereotactic Radiation Therapy and non-Stereotactic Radiation Therapy users were 3D-conformal (88%), non-computerized (manual (71%), intensity-modulated (59%), stereotactic (55%), image-guided with on-board planar imaging (KV or MV) (48%), image-guided with on-board CT or camera guidance (36%), and other (21%).

Of the 66 participants who provided information on SRT usage, 55% said they performed SRT at their facility, 33% did not provide SRT but referred cases to other facilities for SRT, and 12% neither provided nor referred SRT. 17 respondents said they performed remote treatment planning and of those, 41% created SRT plans for delivery at a distant practice. SRT usage was more prevalent in academia (including combined academic/private facilities) than in private practice-only facilities (69% versus 41%).

All SRT users and 90% of non-SRT users said that a board-certified radiation oncologist was involved in the delivery of RT. All SRT users said they had a medical physicist in some capacity unlike 62% of non-SRT users. All participants were asked to define SRT in an open-ended, free text survey question to learn how clinicians characterize SRT in veterinary medicine, with 96% of respondents providing SRT definitions.

The most common SRT definition term or concept used by the respondents were hypofractionation (64%), conformal (56%), number of fractions (55%), accuracy (39%), image-guidance (37%), high target dose (37%), target localization (25%), and steep dose gradient (23%). With regard to performing SRT treatment planning, the respondents utilized available human literature and guidelines (97%), available veterinary literature (72%), and clinical experience when determining normal tissue dose constraints.

When SRT users were requested to report their overall satisfaction with five different radiation therapy techniques, 62% were “very satisfied” with SRT, 28% were “somewhat satisfied,” and 10% were “neutral.”

Moreover, 79% were “very satisfied” with non-computerized RT (manual), 82% with D-conformational RT, 80% with IMRT and 89% with image-guided radiation (IGRT) with on-board CT or camera-guided imaging. The results highlighted the significance of collaboration to formulate the best practice guidelines and to continue studying about SRT to help practitioners understand how it can be leveraged.



What Are the Types of Radiation Therapy?

1.  Intensity Modulated Radiation Therapy (IMRT)

A traditional standard of care, IMRT delivers small doses of radiation over several fractions or treatments to shrink or destroy tumors. The treatment schedule is usually on weekdays and lasts for two to three weeks, depending on the type of tumor and your pet.

2.      SRT

It is a newer form of therapy being adapted in veterinary medicine. SRT delivers high doses of radiation in a couple of days. SRT can better exclude the surrounding tissues than conventional radiation therapy. There are side effects with this option, but the protocol is shorter.

3.      Strontium Plesiotherapy

It also involves the delivery of high doses of radiation with a small probe. The doses are delivered to a “very small and specific area” and can be used for certain types of tumors like the nasal squamous cell carcinoma in cats.



When Is Radiation Therapy Given?

It may be used as a standalone or in conjunction with other treatments like surgery or chemotherapy, depending on the type of tumor. Radiation therapy is most effective with those that have rapidly dividing cells. However, not all tumors respond to radiation. This treatment can also be used to reduce the size of huge tumors before your pet undergoes surgery to make it more manageable.

Radiation therapy is administered while your pet is under a general anesthetic, as the treatment requires the animal to remain completely still to deliver the radiation with precision. Your pet may need to go through several anesthetic procedures depending on the protocol or treatment program offered by your veterinarian. Radiation is delivered quickly so your pet will only spend a brief moment under full anesthesia for each procedure.

A CT is usually done to “mark” the tumor’s location before radiation therapy is performed, allowing the radiation to be delivered in a precise manner and reducing the damage inflicted on the surrounding normal tissues.



What Are the Side Effects of Radiation Therapy?

Side effects can be divided into early and late effects. The former is usually observed within two weeks after undergoing the therapy and can be felt until a month after the treatment has started. Early side effects are usually inflammatory, commonly affecting the skin and mucous membranes. The treated surface can be red, irritated, or develop ulcers, also known as moist desquamation.

The early side effects depend on the tumor, its location, and the surrounding tissues that may be involved. For example, if your pet’s mouth is being treated, the side effects can include bad breath, excessive salivation, plaque or ulcer formation, and secondary infections. If your pet experiences the aforementioned side effects, it will be provided with medication to treat the infections and relieve pain.  

Oftentimes, late side effects happen more than six months after the treatment, which is also dependent on the tumor and the surrounding tissues that may be involved. Your veterinary oncologist will provide information about the possible side effects you need to be aware of.


Before deciding to let your pet undergo radiation therapy, make sure that you discussed with your veterinary oncologist about the possible side effects of the procedure. Don’t worry, veterinary teams will ensure your pet’s comfort and happiness during and after the therapy.