Pet Radiation Treatments
The Varian Trilogy Linear Accelerator with RapidArc technology allows image guided treatment for many types of cancer. There is no need for scalpel surgery first. The treatments can be completed in just one to three days with millimeter precision.
The process starts by building an immobilization device while your pet is lightly anesthetized. This personalized cast of your pet helps to hold them in the correct position for the CT scan which is required for treatment planning. The same cast will be secured to the Trilogy table so that the position can be reproduced for each SRS treatment.
Once the CT scan is produced, the information is used to build a three-dimensional model of your pet within the. Organs At Risk (OAR) such as the eyes, the lenses, the brain and the spinal cord are identified, as is the tumor. The computer aids in designing a plan that will deliver as much radiation to the tumor as possible while keeping the dose to the normal structures at a safe and acceptable level. This process can take as many as a few hours to complete for each patient. Once Dr. Boshoven feels the plan is optimized for your friend, it is sent to another radiation oncologist for review. With the very large doses of radiation being delivered and the often critical structures near the cancer, we feel this is a vital step in the safe delivery of radiation to your pet. We also deliver each plan to a phantom. A Phantom is a device that measures the amount radiation as well as the shape of the radiation to ensure that we can accurately deliver the plan the computer recommends. Once all of these steps are completed, we can then bring your friend back into the hospital for the treatment. The planning phase takes between two and five days to complete.
When your pet comes in for Stereotactic Radiosurgery, he or she will be lightly anesthetized for about 15 minutes total. They are placed into the immobilization cast again. The Trilogy then performs another CT scan using its on-board imaging. This CT is compared to the planning CT so that the position can be confirmed with millimeter accuracy. Once the two CT scans line up, the treatment can be initiated. The average treatment takes about four minutes while the linear accelerator rotates around your pet, typically two times.
Side effects are limited to the area treated and are quite minimal compared to conventionally fractionated radiation therapy. Typically, about 10-14 days after treatment, we see some hair loss in the area that was treated. This hair usually grows back but this often takes a few months. When it grows back, it usually grows back white. Occasionally, blisters in the radiation field can be seen during that same time frame and typically progress over about a week’s time and then heal quickly after that. If the tumor is in the nose and penetrates the mouth, an oral nasal fistula can develop when the tumor recedes. Side effects like dry-eye and cataracts can occur if the eyes are within the radiation field.
Tumors that can be treated with stereotactic radiosurgery include sarcomas and carcinomas in most locations within the body. Tumors that cannot be surgically removed are great candidates for this treatment as there must be a target for us to aim at. Tumors within the brain, the nasal cavity, the lungs and the abdominal cavity are all potential SRS patients.
Conventionally Fractionated Radiation Therapy utilizes photons or electrons delivered by a Varian Linear Accelerator to treat certain cancers. This type of radiation has been used in human medicine since the end of the 19th century. Pioneers like Marie Curie and Wilhelm Roentgen realized very early on that radiation could be delivered to patients to treat tumors. Emil Grubbe treated a woman with breast cancer with radiation who survived years after her treatment and as such, Dr. Grubbe was the world’s first radiation oncologist. Claude Regaud was the first to realize that the body would tolerate larger doses of radiation if the delivery was broken into smaller fractions delivered over many days rather than all at once. Fractions are individual treatments delivered daily or sometimes weekly that when added together make up the total treatment dose. This concept of “fractionated” treatments is still the most common type of treatment used today.
When a human is treated with radiation, they simply sit or lie down on a table, hold still for a couple of minutes, receive treatment and get up and go home. For our animal patients, we must utilize anesthesia so that they remain perfectly still while they are in a dark room, on a table, by themselves. The anesthesia that we use is very light and very short. We don’t need to use sedatives or tranquilizers for these patients. Sedatives and tranquilizers are often what lead to the “anesthesia hangover,” so our patients do not have these lasting effects. Following each radiation treatment at Arizona Veterinary Oncology, our patients are wide awake and ready to go home and experience a normal day.
For the first few weeks of fractionated radiation treatments, you won’t see anything different in your friend other than a bad haircut. We may need to shave some areas around the radiation site and use colored markers to assist with the daily setup. By the end of the third week of treatment, you may see side effects within the area that is treated (called the radiation field). Our pets do not experience side effects like radiation sickness (some humans experience vomiting and diarrhea associated with radiation treatments). At first, you may see some hair loss. This area often will progress to what is called moist desquamation. This is like a blister that has had the skin come off. This area will be tender and will bleed easily. The week after the last radiation treatment is when the side effects will be the worst. A week or so later they will be healed. It is not uncommon to have the blister-like lesions for about 2-4 weeks total. During that time, your dog or cat may be placed on antibiotics and/or pain medications. The hair typically regrows but it may take a few months for this to happen. When it does, it usually grows back white.
This type of radiation is most often used when a tumor has been removed by a surgeon and cancer cells were left behind. Soft tissue sarcomas and mast cell tumors in the skin are two common examples of when Arizona Veterinary Oncology would use conventionally fractionated radiation therapy.
Palliative radiation treatment in pets is radiation designed to make your pet feel better. While this type of radiation is not designed to make your pet live longer, it very often can make your friend feel better and have a better quality of life. The most common use of palliative radiation occurs in tumors that cannot be surgically excised. The type and location of the tumor determines the number of radiation treatments and the effectiveness of those treatments. Often radiation is given once per week for four to six weeks. Side effects with this type of radiation are minimal but can include hair loss in the treatment field. Blister like lesions are rare but do occur, particularly when the treatment involves the oral cavity. You pet will need to be anesthetized for these treatments. The anesthesia is very light and short, so though not risk free, it is considered low risk.
One of the best uses for palliative radiation occurs in dogs with osteosarcoma of the long bones. For this type of radiation, your dog would come in two days in a row and receive treatment each day. Each one of these treatments requires a light and brief anesthesia. There are no sedatives or tranquilizers required in most cases and therefore your pet will not go home with an anesthesia hangover. The anesthesia time for these treatments is generally 15 to 20 minutes. Following the radiation treatments, research suggests that 74 to 92% of dogs with osteosarcoma receive significant pain relief. This pain relief often lasts between one to three months. It usually occurs within one week of the treatment. There are generally no side effects with this type of radiation, although sometimes pets will lose hair in the radiation field. It is possible to repeat the treatment in the future and very often we get pain relief a second time and sometimes even the third time with these dogs. As noted above, this treatment is not designed to make your friends live longer. The average survival time with this type of treatment for dogs with osteosarcoma is about 2 to 4 months. Our biggest fear as long as the diseased leg remains is a pathologic fracture. This occurs when the weakened bone breaks and your dog gets suddenly much more uncomfortable. This can happen at any time with them doing virtually anything. Unfortunately, there is no good solution once this occurs. Our only options should this happen would be amputation of the leg or euthanasia. Minimizing potential stressors on the leg (such as jumping out of the car or off the bed) will reduce the chance of this happening but will not eliminate it.
Another common use of palliative radiation is for cats with oral tumors. This type of radiation is often performed once per week for 4 to 6 weeks. As noted above, the anesthesia time is very short. Also, as with our dogs with osteosarcoma, side effects are uncommon. Hair loss in the radiation field is not unusual. In some cases, there can be some mild blister like lesions that occur inside the mouth. For most of our cats with oral tumors that are treated this way, survival times are typically only a few weeks to months. With this treatment, we hope they will eat a little better and that pain from the tumor, often invading into the bone, will be reduced.
While palliative radiation treatments in pets are not designed to make our dogs and cats live longer, it can often significantly improve the quality of life. This treatment is often combined with medications to also help with pain control. NSAIDs, Tramadol and Gabapentin are common examples of medications used to help control pain. In cats, Buprenorphine is also commonly used. At Arizona Veterinary Oncology, we think that the importance of quality of life far exceeds the importance of quantity of life. Talk you your veterinarian and see if palliative radiation is an option for your beloved pet today.