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 Radiation Oncology: Radiation Therapy for Brain Tumors 

Does my pet have a brain tumor?

  • Brain tumors commonly cause behavioral changes, gait abnormalities and/or seizures. Some types can cause facial muscles to shrink (trigeminal nerve sheath tumors), while others can cause hormonal imbalance (pituitary tumors).
  • The diagnosis is often made with an MRI; other tests (CSF taps, biopsies and blood testing) may also be used.)

What is the prognosis?

  • Brain tumors are rarely curable. Without treatment, pets rarely survive more than a few months.
  • In most cases, the best prognosis is associated with surgery, radiation therapy (RT), or a combination of both.
  • Many pets will have improved quality of life, and can live a year or more after RT of their brain tumor.
  • Prognosis is influenced by several factors, including how big the tumor is, where it is within the brain, the type of brain tumor and the type of treatment.
  • Although it is very uncommon for brain tumors to spread to other parts of the body, it is possible for other types of cancer to spread to the brain. Tumors that have spread to the brain (called metastatic brain cancer) are treated differently, and have different prognosis than the more common types of brain tumors. Because of this, we usually recommend doing bloodwork, chest X-rays and an abdominal ultrasound to examine your pet for other types of cancer before pursuing any type of radiation therapy for brain tumors.

Image from a radiation plan, showing the dose of radiation as a “color wash”, overlying the CT scan. The red/orange areas show the high dose, while blue and green are low doses.

What are the treatment options?

  • Medical management: steroids and/or anti-seizure medications can be used to manage the symptoms of brain tumors. These treatments are aimed solely at improving/maintaining quality of life. Because these medications don’t have direct effects on the tumor itself, they are unlikely to improve the chance of survival.
  • Chemotherapy: as a general rule, chemotherapy is not a very effective treatment when used as the primary treatment for brain tumors in pets.
  • Surgery: some brain tumors are very effectively treated with surgery.
  • Radiation therapy: RT can be combined with surgery, or can be a very useful alternative to surgery.

Navigating the options:

  • Most brain tumors can be treated with either IMRT or SRT. There are advantages and disadvantages to both.
  • SRT is more convenient, and often a bit less expensive than IMRT. However, it is not an appropriate treatment for all brain tumors. For example, SRT can be used for pituitary tumors and trigeminal nerve sheath tumors in dogs, but IMRT is the preferred treatment for most dogs with these tumors, whereas SRT is the preferred treatment for most dogs with meningiomas.
  • Your radiation oncologist will review the options in more depth, after reviewing the MRI or CT scan, and your pet’s overall condition to determine the safest and most effective treatment.
  IMRT SRT
Description A conventional, full-course of “definitive-intent” RT, given with new beam shaping and image-guided technologies to
minimize the risk of severe side effects.
Also commonly referred to as SRS (stereotactic radiosurgery), GammaKnife® or CyberKnife® treatment. Uses accurate and precise
techniques to deliver high doses of radiation to a tumor in a very short period of time.
Schedule
20 treatments, given once daily, 5 days a week (M-F) 1 to 5 treatments, given on consecutive days. The total number of treatments depends on the type and size of the tumor as well as individual risk factors.
Approximate cost* $6,500 - 7,500 $6,000 - 7,000
Brain tumors that are commonly treated
Pituitary tumors (especially in dogs)
Trigeminal nerve sheath tumors. Some meningiomas
Meningioma
Glioma
Pituitary tumors (feline acromegaly)
Trigeminal nerve sheath tumors

*Cost estimates include a radiation oncology consultation, CT scan, RT planning, quality assurance testing, anesthesia and radiation treatments. 

Side Effects of Radiation Therapy:

  • During RT: there is always a risk that pets undergoing anesthesia for treatment of a brain tumor will have a fatal complication, and not wake up from their treatment. Fortunately, this is very rare.
  • Acute side effects: most pets will be a bit sleepier than usual for 1-2 weeks after RT, but can still undergo all of their normal activities, and maintain a good quality of life.
  • Early-delayed side effects: up to 40% of pets can have worsening of their original symptoms in the first 1-5 months after RT (due to irritation of the normal brain tissue surrounding the dying tumor). Symptoms are usually mild and resolve in a week or two. Medications might be used to support your pet through this period. Rarely (fewer than 5% of cases), these side effects can be more severe, and could even result in death.
  • Late side effects: more severe and long-lasting side effects are possible, but quite rare, and occur months to years after treatment. Your radiation oncologist will talk more about these risks during consultation.

Follow-up after radiation therapy:

  • Most pets will be prescribed a course of steroids to be used for the first 6 weeks or so after RT. It is important that these drugs not be stopped abruptly!
  • We usually recommend recheck exams, 3 and 6 weeks after RT, with your pet’s neurologist or radiation oncologist.
  • We often recommend a follow-up MRI or CT scan 3-4 months after RT. This scan shows us how well the radiation is working, and can help guide future decisions about treating your pet’s cancer.

Facts about radiation therapy:

  • Performed on an outpatient basis. Patients typically arrive at the hospital in the morning. Families are called and come pick their pet up after they have received that day’s treatment. This is often in the afternoon.
  • Painless. Pets are anesthetized for each radiation treatment. Anesthesia is not used to prevent pain. Instead, it is to make sure the patient remains perfectly still while being treated. This ensures that the highly focused radiation beams hit and destroy the tumor, rather than adjacent tissues.
  • Radiation therapy is safe for families. The types of RT used for treating brain tumors do not make your pet radioactive. There is no danger for you or your family to interact with your pet after they have received RT for brain cancer.
  • Radiation therapy does not work overnight. The goal of RT is to stop the tumor from growing. In many cases, radiation will also cause the tumor to shrink. But it can take weeks to months for that shrinkage to occur.