Veterinary radiation therapy without the mystery

When clients hear the word radiation come up in their pet’s cancer diagnosis, it's natural for them to feel uncertain. Some clients, and possibly even some veterinary professionals, associate radiation therapy with harsh adverse effects, last-resort desperation, or science fiction–level complexity. During her lecture at the 2026 Fetch Nashville Veterinary Conference, Siobhan Haney, VMD, MS, DACVR (RO), MBA, broke down veterinary radiation oncology to help general practitioners understand how it works, who is a good candidate, and how veterinary teams can address common misconceptions and myths when talking about radiation oncology.

How it really works

Radiation therapy works by damaging the DNA inside tumor cells, preventing them from dividing and causing them to gradually die off. Critically, this is a local treatment because it acts only within the treatment field, not throughout the entire body. This makes it fundamentally different from chemotherapy, which circulates systemically. Adverse effects from radiation are largely predictable and confined to the area being treated, which makes the risk profile highly manageable when the treatment is properly planned.

One of the most important things to understand is that radiation therapy isn't a single protocol. Every treatment plan involves 3 independent decisions: how the treatment is planned, how it is delivered, and what the intent of the treatment is.

Planning can range from manual approaches to advanced CT-based 3D planning for more complex cases. Not every patient needs the most sophisticated planning available, and simpler plans can still deliver excellent outcomes.

On the delivery side, 2 modalities often come up: intensity-modulated radiation therapy (IMRT) and stereotactic radiation therapy (SRT). These serve different clinical purposes. “I really love to use IMRT for urogenital tumors, where it's really important to be very sparing of the normal tissue in that area,” Haney told attendees.

SRT delivers high, precise doses in just 1 to 5 treatments and is ideally suited for small, well-defined tumors. IMRT uses many lower-dose fractions spread over several weeks and is better suited for larger tumors, infiltrative disease, or microscopic residual cancer following surgery. Matching the right tool to the right tumor matters enormously.

“Finally, we have stereotactic radiation therapy. That's just…a different way of delivering radiation. We'll use stereotactic radiation therapy for very small and very well-defined lesions, like brain tumors, or we'll use it for nasal tumors when the edges are very well defined and when we want to deliver a very high dose of radiation to our treatment area, but a very rapid fall off of dose of radiation, so that normal tissues surrounding the tumor receive a far less dose of radiation,” Haney said.

Finally, treatment intent shapes the entire approach. Definitive radiation aims for long-term tumor control. Palliative radiation, on the other hand, focuses on relieving pain and improving comfort, particularly valuable for patients with bone tumors, advanced disease, or cases where aggressive treatment isn't feasible or desired.

Dispelling the myths

Perhaps one of the biggest barriers to appropriate radiation referrals is misinformation.

“Radiation therapy does not make a patient radioactive; they're not going to glow in the dark. It doesn't cause systemic effects, so no vomiting, diarrhea, fatigue, or things like that. We do need to utilize anesthesia, so sometimes there will be lingering effects from anesthesia, but otherwise, the radiation itself doesn't cause any of these signs,” she said.

“We also know what the radiation is going to do, so we're using it in a very controlled fashion, and we're pointing that beam of radiation exactly where we know it's going to go so we can predict what kind of [adverse] effects we're going to see. So we're not destroying normal tissue to the point of incapacitation, we're not causing effects outside of the radiation fields, and we're certainly not subjecting patients to any unnecessary pain or discomfort,” Haney continued.

Haney also reminded the room that radiation is not a treatment of last resort. Increasingly, it's used as a first-line option or in combination with surgery, particularly when a tumor is near critical structures, surgical margins are incomplete, or surgery isn't an option at all. Most animals also tolerate treatment well, with temporary, localized adverse effects that are actively managed throughout the process.

Reference

1. Haney S. Radiation 101: demystifying cancer treatment for your patients. Presented at: Fetch Nashville Veterinary Conference; May 28-30, 2026; Nashville, TN.