Stereotactic radiation therapy is a powerful tool in the NC State Veterinary Hospital’s arsenal, attacking cancerous tumors of the brain, spine and those that can reach the heart, all while still protecting normal tissue. Conventional radiation therapy is typically used over many weeks. SRT can often be conducted during just a handful of hospital visits.
New NC State College of Veterinary Medicine research suggests SRT may now be an effective option in treating canine multilobular osteochondrosarcoma, or MLO, a rare cancer that starts in the bone, commonly grows on the head and is most often seen in middle-aged and older dogs.
The study, published in Veterinary and Comparative Oncology, is believed to be the first to outline using SRT to treat canine MLO. Its authors are Hiroto Yoshikawa, Tracy Gieger, Michael Nolan and radiation oncology resident Katherine Sweet. We spoke with Sweet about the research team’s promising findings.
What does your study suggest about the potential of SRT to treat canine MLO?
Surgery to remove the tumor remains the treatment of choice for MLO. However, since the tumor type most commonly arises from the skull, the risks of surgery can be unacceptable to some.
Although the dogs included in this case series had a shorter average survival than dogs treated with multimodal therapy, SRT can be an attractive option for owners who wish to pursue non-surgical treatment options that are more intensive than medical management or more conventional palliative-intent radiation therapy.
When compared to full-course radiation therapy, SRT has improved owner convenience and has fewer anesthetic episodes. The higher doses per treatment used in SRT may also have an advantage biologically with this tumor type.
How does SRT compare with traditional approaches to treating the condition?
SRT has promising tumor shrinkage, improvement in tumor-associated symptoms and improved survival when compared to previously reported medical management. But it is multimodal therapy — surgery followed by radiation therapy and/or chemotherapy — that has been reported as having the longest survival times for dogs.
Compared to surgery, the benefits of SRT include reduced risk of immediately fatal complications and that treatment can be performed on an outpatient basis. This is an acceptable trade-off for some parents who face a lower-average overall survival time for their pets.
With often fewer treatments compared to a more traditional radiation therapy protocol, the higher intensity of treatment with higher doses of radiation delivered per treatment would theoretically provide a greater benefit.
Did anything surprise you about the results of the study? Was there something that was particularly encouraging?
The expectation of using SRT for this disease was to stop tumor growth to delay progression of symptoms. This could help dogs survive longer by delaying worsening of symptoms.
The thing that we found surprising was that several of the dogs had shrinkage of the tumor rather than simply a stabilization in size. Since symptoms are often associated with compression of the brain or other sensitive nearby structures by the tumor, tumor shrinkage can result in improvement in symptoms.
You note in the study that canine MLO is rare, but what kind of impact does it have on the health of dogs?
The symptoms associated with MLO vary widely depending on where the tumor originated from and what tissues it compresses as it grows. It originates most commonly from the bones surrounding the brain, so in addition to causing brain compression tumor growth there can be profound neurological impairment that could be fatal if left untreated. Other symptoms could include ocular discomfort and damage, respiratory impairment, difficulty eating and more.
The CVM has led other studies using SRT to treat different types of tumors. How would you describe the potential of the therapy approach in veterinary medicine?
SRT requires advanced technology that is recently becoming more available in veterinary hospitals to allow delivery of high doses of radiation accurately and precisely to the tumor while limiting the dose to surrounding normal tissues. This means fewer treatments and generally minimal side effects associated with treatment.
Although not suitable for use for all tumor types or even in all pets with the same tumor type, it can be an attractive treatment option in many cases by limiting the number of hospital visits and allowing the pet to be at home with their family.
Learn more about stereotactic radiation therapy at the NC State Veterinary Hospital here.
Learn more about the hospital’s small animal radiation oncology service here.
~Jordan Bartel/NC State Veterinary Medicine