Survival times are important but most owners want to know if their dog is going to
feel better with radiation therapy (RT) following a brain tumor diagnosis. Ultimately, that is what drives us to do these procedures too, isn’t it? A study was published in the Journal of Veterinary Internal Medicine (Russli et al 2026:40(2)) that strove to answer this question. Spoiler alert – the dogs DO feel better!
M & M
· 106 dogs with an imaging-diagnosed primary intracranial tumor were included in a prospective, randomized controlled trial. What is a primary tumor? Tumors such as a meningioma (45%), glioma (36%) or pituitary tumor (19%) are primary tumors.
· All dogs underwent 10 fractions of radiation therapy over a 2 week period.
· Medical therapy was individualized (i.e. seizure management, steroids) and often started before RT,
Important Results
· At initial diagnosis 75% of dogs were noted to have moderate disability and 21% had a severe disability. These classifications are not standard which makes this difficult to compare across studies. The disability scores were performed multiple times throughout the study giving a wonderful internal control set for each dog.
· Medical management resulted in significant improvement in their neurology dysfunction score (this was BEFORE radiation was started)
· Additional improvement was noted during RT and by the end of treatment only 38% had detectable neurologic deficits.
Other Interesting Results
Most tumors substantially shrank with RT. How much did they shrink by 6 months post-RT
· Presumptive meningioma had a mean volume reduction of 39%
· Presumptive glioma had a mean volume reduction of 83%
· Pituitary masses had a mean volume reduction of 47%
Importantly, mean tumor volume did not predict neurologic deficits well. This isn’t surprising because the brain is more concerned with the time-to-adaptation than the total volume of a tumor. This means if the tumor grows rapidly (sudden bleed) clinical signs are likely to be more severe than if the tumor grows slowly. Shifts in intracranial pressure, the degree of infiltration and seizure activity (to name a few) also play an important role in neurologic disability.
Lastly, seizures responded well to radiation therapy! Over ½ of dogs were seizure free and the median time to seizure recurrence was 12 months in the seizure-free population. Most importantly, the seizure recurrence correlated with tumor progression. This means if a patient undergoes RT and becomes seizure free, any break through seizure should be an indication of possible tumor progression. Of course, all dogs were continued on their antiseizure medications during this time so we cannot attribute their seizure freedom to RT alone.
Key Point
This study highlights that clinical improvement is likely with steroids, and also likely to get a boost from RT. Based on other studies we know that RT is likely to result in longer survival times than steroids alone and that is the reason that we recommend RT, not just the clinical improvement. However, additional improvement was noted in many dogs beyond what medical management provided and that is a nice tidbit to take away from this study!
Lastly, this study supports the notion of “treat the patient not the MRI”. A very large tumor may be clinically less severe than a small, rapidly growing one. Treat the patient’s clinical signs with medications and let the radiation deal with the tumor growth. Ask – “how well is the patient functioning, not how big is the tumor?”
Thanks for reading! If you work with (or know) a newly graduated veterinarian that might enjoy reading these TidBits please ask them to sign up online or email me and I’ll add them. (You can forward this email and they can reply to me.) Let’s keep the knowledge flowing! I hope you have a great week!