Stereotactic radiation (SRT) & Intensity Modulated Radiation Therapy (IMRT)

Stereotactic radiation (SRT) and Intensity Modulated Radiation Therapy (IMRT) are becoming more readily available for animals. In the past, traditional radiation therapy to treat cancer in pets would usually result in significant side effects and many owners would decide not to pursue treatment because of this. IMRT and SRT are changing the way that we are able to treat cancer in pets, and they have great potential to improve both your pet’s quality and quantity of life. The Veterinary Cancer Center is pleased to be able to offer these treatments for pets with cancer.

What is Stereotactic Radiation or Stereotactic Radiosurgery?

Stereotactic radiation, also known as stereotactic radiosurgery, involves delivering a small number of large radiation doses to the tumor, in the hope of causing maximal tumor damage while limiting the dose to the normal tissues. Usually this is done in 1 to 3 treatments over a short period of time. With stereotactic radiation, a large number of beams are directed at your pet from all different angles and the shape of the radiation beam is changed, during treatment, to deliver radiation where it is needed most. 

What tumors can be treated with SRT?

SRT can be used to treat a variety of tumors, including brain tumors, pituitary tumors, nasal tumors and other tumors involving the head and neck. It also can be used to treat tumors of the spine and some parts of the abdomen or chest. It can be used for pets when daily visits and anesthesia may be too dangerous. 

What is Intensity Modulated Radiation Therapy or IMRT?

IMRT uses the same technology as SRT with a large number of beams to attack the tumor from all angles while each beam is shaped to precisely deliver the radiation where it needs to be directed. With IMRT similar doses are used that have been used for conventional radiation in the past. However, IMRT allows the dose of radiation to be targeted at the tumor, with great precision, to avoid treatment of the normal tissues. This allows the same or higher doses of radiation to be delivered directly to the tumor, with fewer side effects for your pet. 

What tumors can be treated with IMRT?

IMRT can be used to effectively treat nasal tumors, brain tumors, pituitary tumors anal sac carcinomas and a number of other tumors. In any location where radiation side effects might be a problem, IMRT can be used to help minimize them. 

Why does my pet need another CT scan for treatment?

If your pet with cancer has already had a CT scan or an MRI to diagnose their tumor, they may need a second CT scan for radiation planning. The first CT or MRI is useful to help determine where your pet’s tumor is, but the radiation planning CT is necessary for your pet for treatment. With newer radiation technology, as we tighten, or conform, the does tightly around the tumor, it is critical that your radiation oncologist know exactly where they are treating. Therefore a second CT scan is often necessary for this. Usually, your pet will be placed in a positioning device such as a bite block and/or vacuum bag, to make sure that they are positioned the exact same way for the CT scan and for each treatment. The CT scan requires a short anesthesia, but it is well worth it to make sure that your pet is receiving the most accurate delivery of their radiation dose. 

What are the potential side effects for my pet?

One of the main benefits of IMRT and Stereotactic radiation is that they can minimize the side effects from radiation, making treatment much more tolerable for you and your pet. With traditional radiation treatments there are often significant side effects in the local area from damage caused by the radiation. With IMRT and SRT the dose of radiation can be targeted very tight around the tumor, using a radiation plan that is customized for your pet, minimizing the dose of radiation that is given to your pet’s normal tissues. In some areas, such as the head or pelvis, this is critical for avoiding severe side effects. For example, traditional conformal radiation for nasal tumors in dogs usually results in severe inflammation and burning in the mouth, around the eyes and the skin of the face.

There is also a risk of a severe, long-term complication in the eyes, the brain or the local bones. With IMRT and SRT, the dose of radiation to these structures can be minimized, limiting side effects to small areas. This means a better quality of life for your pet. With any type of radiation treatment a brief anesthesia is usually required. This anesthesia is needed to make sure that your pet stays perfectly still for each treatment. It is usually a short anesthesia, and your pet is monitored very closely while under anesthesia.

Even when radiation patients have anesthesia every day, the risk of significant complications is very low. Your radiation oncologist will evaluate your pet to make sure that they are likely to handle the anesthesia well and may recommend additional staging tests, such as radiographs, ultrasound, an echocardiogram, bloodwork and or urinalysis to help make sure that your pet is a healthy candidate for anesthesia. Another potential benefit of SRT is that it may be able to limit the number of treatments that your pet will need, minimizing the risk of anesthesia complications. 

How can I find out more about IMRT or SRT for my pet?

If your pet has been diagnosed with cancer, and you want to learn whether IMRT or stereotactic radiation would help your pet, you should make an appointment to meet with our radiation oncologist, Dr Farrelly. We will evaluate your pet and their medical records and talk to you about what type of treatment options are best for your pet.