As a radiation oncologist one of the tumors that I have disliked treating the most are nasal tumors in dogs. Nasal tumors usually fill up one or both sides of the entire nasal cavity and sinuses. In a dog’s head this means that the tumor is basically wrapping around the eyes and the brain and the tumor sits right above the mouth. So when we treat these patients we usually have to include a great deal of the mouth the eyes and the brain. In some dogs, treating these areas causes severe short-term side effects, and animals are usually very painful during and for a few weeks after radiation. We have much better pain medications so it is possible to get these patients through their treatment, but for many pet owners and their animals treating a nasal tumor is a difficult decision and I feel that a lot of dogs were not treated because of these side effects.
With the advent of newer radiation technologies this has changed. Intensity Modulated Radiation Therapy (IMRT) is a newer radiation technique that is becoming available to treat difficult tumors like nasal tumors. With IMRT the patient is positioned in a positioning device so that their head is very still, and a CT scan is done not only to identify exactly where the tumor is, but also this CT scan is used by a three-dimensional treatment planning computer. Radiation beams are aimed at the tumor from a number of different directions so that the radiation can approach from all sides. Then the radiation oncologist tells the computer what dose they want to give to the tumor as well as the maximum dose they want to give to the important normal tissues. Then the computer figures out how to accomplish this. For each field, small leaves up in the head of the radiation machine are used to deliver different doses of radiation to different parts of the field. For example, if one of the fields is pointed at the tumor and the brain, the field might give little or no radiation to the brain while at the same time giving a high dose to the tumor.
For dogs with nasal tumors this means that the radiation can be directed to the tumor and the dose to the normal tissues is minimal. Dogs that are being treated with IMRT usually have small areas of redness and irritation in their mouths, but most of their mouths, eyes etc. have little to no significant side effects. This means dogs are much more comfortable going through treatment, but also it most likely will decrease the number of permanent side effects, making radiation much safer.
Dr. John Farrelly