In a previous blog I mentioned how we use technology to minimize side effects to our pets when treating them with radiation. However, there are many situations where we cannot or do not want to completely avoid normal tissues. Almost all tumors have microscopic cells that extend into the surrounding normal tissues. We often use the analogy of an octopus to describe a cancerous tumor. The body of the octopus is the part of the tumor that we can see either with our eyes, or by some imaging (such as ultrasound, CT scan, MRI etc.). If we just needed to treat this cancer would be easy to cure with surgery. The cancer cells that extend into the normal tissue, like the arms of an octopus, often cannot be removed with surgery and these are often what we are treating with radiation or chemotherapy. When we treat these cells we usually have to treat the normal tissues that they are invading into and this results in side effects in the normal tissues.
Radiation side effects in animals can be severe in some cases, but we are able to manage them, to get pets through treatment. They usually start around the middle of a course of radiation, but they can get worse for up to a week after treatment is finished. When the skin, the lining of the mouth, the eye or the colon is treated these side effects usually include redness and irritation of the area. This looks a lot like a sunburn. It starts as mild redness and itch, but usually gets worse until the area is very red and/or ulcerated. When this happens pets usually need pain medications, anti-inflammatories and antibiotics to help keep the animal comfortable. Fortunately we have many more pain options available for dogs and cats to help get them through this time. The area is usually itchy so it is also very important that animals not be allowed to lick or chew at the area, so sometimes they need to wear a cone type collar to prevent this.
Fortunately for cats the short-term side effects are usually much less severe than in people or dogs. Most cats who are treated with radiation usually just get dry, flaky skin or mild redness in the radiation area and they usually are not very painful.
Long-term side effects from radiation usually do not cause problems, things such as changes in hair coat color or thin skin. Fortunately dangerous long-term side effects, such as bone destruction or radiation induced tumors, are typically very rare and can take many years to develop.
Although side effects from radiation can cause significant pain and discomfort, the radiation protocols that we use to treat animals are designed to try to minimize these effects so that we can get pets through treatment with as little discomfort as possible.