When a dog is diagnosed with cancer, very rarely is the aim of treatment an outright cure. Instead, veterinarians usually try to maximize the amount of time a dog can survive while enjoying a good quality of life.
One way we can do this is through palliative radiation therapy (PRT). The goal of this type of radiation treatment is not to completely eliminate a tumor (although that sometimes does happen), but to reduce the adverse effect it is having on a dog’s body. As tumors grow they often cause pain, may physically block a part of the body from functioning adequately (e.g., the passage of feces through the colon), and can bleed, all of which drastically reduce a dog’s quality of life. Palliative radiation therapy can eliminate, or at least reduce, all of these symptoms for a period of time.
One limitation to the recommendation of radiation treatment in dogs has been a lack of data regarding just how well it works. It’s hard for owners to commit to the time and expense of PRT when hard data on their dog’s prognosis is lacking. A study published in the January 1, 2016 issue of the Journal of the American Medical Association evaluates aims to correct that.
The researchers looked at the medical records of dogs who received PRT at University of Pennsylvania Matthew J. Ryan Veterinary Hospital between July 2007 and January 2011; 103 dogs were included in the study. Because of the variety of tumor types and body locations, different radiation protocols were used.
In this study, the average overall response rate to palliative radiation therapy was 75 percent, but it “varied among tumor types and ranged from 50% to 100%.”
Here’s a simplification of one of the tables presented in the paper that provides details from this study, along with those of others that looked at the effectiveness of PRT.
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It is important to understand that the overall response rate was calculated by adding the number of dogs that had a complete response (disappearance of all measurable tumors and clinical signs associated with them), partial response (decrease in tumor size of more than 50% and an improvement of clinical signs), and stable disease (less than 50% decrease in tumor size or less than 25% increase in tumor volume with no apparent change in clinical signs) following PRT together and dividing that number by the total number of dogs in the category. Therefore, it is a very general number. It becomes more useful when you combine it with the median survival time and the lowest and highest survival times reported in the parenthesis that follow.
Here’s an example of how to work the numbers from this study. If you have a dog with a nasal tumor, there’s a 67 percent chance that palliative radiation therapy will at least stop the progression of the tumor and perhaps even shrink or visibly eliminate it.
The “typical” dog will survive for almost nine months after PRT, but you should be prepared for anything between three weeks, if your dog does not respond, to over 1 ½ years, if he responds exceptionally well.
Palliative radiation therapy for solid tumors in dogs: 103 cases (2007-2011). Tollett MA, Duda L, Brown DC, Krick EL. J Am Vet Med Assoc. 2016 Jan 1;248(1):72-82.