What is Stereotactic Radiation Therapy (SRT)?
Stereotactic Radiation Therapy (SRT), also known as “Stereotactic Radiosurgery, Cyberkinfe, or Gammaknife,” is an advanced type of radiation therapy delivery that uses a variety of specialized technology to precisely deliver a very high dose of radiation to a tumor, while simultaneously protecting and sparing the normal surrounding tissues.
Will my pet have surgery with SRT?
No; SRT is a non-surgical, non-invasive procedure. The term “surgery” is sometimes used to describe the treatment because the delivery of the therapy is as precise as a surgeon’s scalpel blade.
What patients are good candidates for SRT?
While many different tumor types in various locations throughout the body can be treated with SRT, not every patient is a candidate for this procedure. This therapy requires a “gross” or “bulky” tumor that will serve as a “sink” for the high doses of radiation therapy to be delivered. Therefore, patients who have had surgery to remove their tumors are not candidates for SRT (though they would quality for other types of radiation treatments). In addition, some normal organs are more sensitive to radiation therapy than others, so the site and overall extent of the tumor within the body is also an important consideration for SRT candidacy.
Some common tumor types that are treated with SRT include:
- Brain tumors
- Intranasal or sinus tumors
- Oral tumors (including melanoma, squamous cell carcinoma, fibrosarcoma, osteosarcoma)
- Bone tumors (throughout the skeleton including the limbs, spine, pelvis, and skull)
- Tumors of the prostate
- Lung tumors
What are the logistics of a course of SRT?
First, a consultation with a Radiation Oncology will determine if you pet is a good candidate for SRT, and also allow you to discuss the specific ins and outs for your pet’s treatment.
Next, a CT scan is performed to: 1) determine the precise internal extent of the tumor; and 2) allow for special software to define the tumor and normal tissues to further enhance the delivery of the treatment. This CT scan is typically performed at the hospital that will be doing the SRT, so we can use patient-specific equipment made specifically for your pet that will further enhance the precision and safety of the treatments.
Finally, the treatment protocols vary from patient to patient, but typically consist of 1-4 treatment sessions delivered either daily (such as Monday, Tuesday, Wednesday, etc.) or every other day (such as Monday, Wednesday, Friday). The protocol is chosen by the Radiation Oncologist to be as effective against the tumor as possible, while still protecting normal tissues.
Is anesthesia required for each treatment session?
Yes; your pet will need to be under full, general anesthesia for each therapy session. Because we cannot be in the treatment room with them during the treatment, it keeps them as safe as possible during the procedure. SRT is a non-painful process, and as such we use much lighter anesthetic drugs than would be used for a surgical procedure. Patients tend to recover much faster than from surgery anesthesia, but may still go home slightly “groggy.” Your Oncology team will discuss your pet’s specific anesthesia and expectations with you during the initial consultation, as well as any other steps or tests that are recommended in order to keep your pet as safe as possible.
Are there side effects from the SRT treatments?
While we are able to sculpt the dose very precisely away from normal tissues, we can still see some side effects from the treatments. These side effects are generally very mild (especially compared to “conventional” radiation protocols) and will go away on their own several weeks after they begin. We typically manage these side effects with anti-inflammatory and pain medications as needed—some patients do not require treatment for them at all. The specific side effects will depend on the type of tumor, its location within the body, and the treatment protocol. The Radiation Oncology team will discuss possible side effects and treatments for your pet with you during the initial consultation.
What is the efficacy/outcome from SRT?
While there are fewer studies with stereotactic radiation therapy in veterinary patients, the data that exists seems to show overall efficacy and outcome from these protocols are similar to previously studied, conventional full-course radiation therapy protocols. Therefore, we often consider SRT as a “definitive-intent” treatment, where we are attempting to control the tumor for as long as possible. There are situations, however, where we attempt to use SRT to alleviate symptoms associated with a tumor, or for palliation. There is thought that SRT may yield longer-term or more “durable” palliation compared to conventional protocols, but there are no studies that prove this quite yet.
What is “Intensity-Modulated Radiation Therapy (IMRT)”?
Intensity-Modulate Radiation Therapy (IMRT) is also known as “dose painting,” and utilizes specialized technology to “push” the radiation therapy dose towards a tumor and away from surrounding normal tissues. These techniques and technologies can be utilized throughout a variety of different radiation protocols, from full-course to stereotactic to palliative, pending the type and location of the tumor and overall treatment goals. Your Radiation Oncologist will discuss the potential benefits and drawbacks of IMRT involved with your pet’s radiation treatment where applicable.