In my last post, I went through some “alternatives-to-amputation,” including palliative radiation and limb-spare surgery. Now we will review stereotactic radiosurgery.
Stereotactic RadioSurgery: radiation instead of surgery
RadioSurgery is used INSTEAD of surgery, when traditional surgery with a scalpel blade is impossible or would cause unacceptable side effects to the patient (for example, in brain or nasal tumors), or when surgery is refused (for example, an amputation for bone osteosarcoma).
Stereotactic RadioSurgery, or SRS, can also be used as a limb-sparing technique. Unlike palliative radiation, which is more about pain relief, this advanced hyper-accurate radiation therapy technique focuses high doses of radiation to damage and kill the bone tumor cells.
I am fortunate to work at a practice that offers CyberKnife RadioSurgery (it’s very rare in veterinary medicine). CyberKnife, a type of SRS, is very conforming to the tumor, which means it follows the contours of the tumor with accuracy. With multiple beams, the CyberKnife robotic arm allows more treatment angles and treats with millimeter to sub-millimeter accuracy. So CyberKnife (CK) radiates less normal tissue around the tumor, and achieves a higher dose to the tumor, all in fewer treatments (3 total for bone tumors). Since the Guide was published, we have since modified our radiation protocol, from 1 session to 3 sessions given on 3 consecutive days. This is a lot less anesthesia, and fewer trips to the hospital, than is typical in conventional radiation.
We were the first animal hospital to offer CK, in 2008, and bone tumors are the third most common tumor we treat. We have treated just over 50 bone cases to date, but some of these have been non-limb locations (skull, jaw bones, vertebral bones). For dogs with osteosarcoma in the limbs, we are seeing better survival times in “good candidates” – patients with enough bone structure left that they are not close to fracture.
Before we use CyberKnife, a CT scan is absolutely required. We need to evaluate the extent of bone destruction from the OSA tumor. We also use it to decide if radiosurgery can be performed at all — and if it can, to carefully plan the radiosurgery.
If the CT scan reveals that the bone is close to fracturing, especially if a lot of cortical bone is destroyed (cortical bone is the very dense, hard outer shell of most bones). we discourage treatment with CyberKnife. Whittling away at a bone that is already close to breaking is just too big a risk to take. It’s really hard for me to break the news to Guardians that are interested in CK that their pet is not a candidate.
So far the results at my hospital show that dogs receiving CK and chemotherapy (to control metastasis) have a survival time of about one year, similar to the survival time for dogs treated with amputation and chemotherapy. If you want to save your dog’s limb, if you can afford radiosurgery, if you can get to a hospital which offers it, and if your dog is a good candidate, this may be a good option to consider.
Don’t forget the chemo!
Surgery and radiation techniques offer local control of the primary OSA tumor, but local therapy is not enough to keep OSA metastasis at bay. Because most dogs (90%) have micrometastasis at the time of diagnosis, and 95% of dogs will develop detectable metastasis, I also recommend chemotherapy. Chemotherapy after amputation, CyberKnife SRS, or limb spare surgery is important to delay metastasis and for long term survival. We will talk about that next.
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Sue Ettinger, DVM. Dip. ACVIM (Oncology). Dr. Sue is a boarded veterinary medical cancer specialist. As a Diplomate of the American College of Veterinary Internal Medicine (Oncology), she is one of approximately 400 board-certified veterinary specialists in medical oncology in North America. She is a book author, radio co-host, and an advocate of early cancer detection and raising cancer awareness. Along with Dr. Demian Dressler, Dr. Sue is the co-author of The Dog Cancer Survival Guide: Full Spectrum Treatments to Optimize Your Dog’s Life Quality and Longevity.