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Cyberknife Robotic Radiosurgery for Cancer Treatment

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INTEGRATIVE PRACTICES focus on individualizing treatment, building health and beginning with the gentlest approaches. The integrative practitioner looks for the least invasive, least toxic approach, with the fewest side effects, to deal with illnesses such as cancer. One of these options is CyberKnife robotic radiosurgery.

Non-invasive alternative to surgery Despite its name, veterinary CyberKnife cancer treatment is a non-invasive alternative to surgery. It utilizes highly-concentrated radiation therapy to eliminate cancerous and non-cancerous tumors without cutting the skin. Radiation therapy is widely accepted as an effective way to treat cancer, but the side effects are more than some patients can withstand. CyberKnife robotic radiosurgery is a form of stereotactic radiosurgery, a highly effective version of radiotherapy that mitigates many typical side effects of conventional radiation therapy, and involves two to three treatments given within a week.

Standard curative intent conventional radiation therapy usually requires between 16 and 22 treatments given daily over the course of a month. It often causes short term reversible side effects such as mucositis, desquamation of the skin, and infl ammation of underlying structures. Although these side effects generally resolve over one to three weeks, they are rarely seen with CyberKnife robotic radiosurgery.

Cyberknife radiosurgery relies on real-time body imaging to guide radiation delivery by an intelligent robotic arm. This technology enables high dose gradients to be delivered with sub-millimeter accuracy to the neoplastic masses and the targets of choice. Because stereotactic radiosurgery is delivered with such accuracy and precision, much higher doses of radiation can be directed at tumors without the concern of affecting surrounding normal tissues. This avoids or minimizes side effects typically associated with defi nitive conventional radiation therapy. This increased effectiveness is why patients typically require fewer than fi ve treatments that can be completed in less than a week.

Treats many tumors CyberKnife radiosurgery can be used to treat tumors in most parts of the body, including the head, spine, lung, prostate, bone, liver, kidney, pancreas and perianal region.

• Preliminary data from one study has shown that stereotactic radiosurgery used for dogs and cats with brain tumors produced median survivals of over 30 months (Veterinary Cancer Society annual meeting, 2011). Another achieved median survivals of over 19.4 months with 92% of patients having an improvement in their clinical signs (Veterinary Cancer Society annual meeting, 2012). In comparison, conventional defi nitive radiation therapy median survivals for brain tumors have been shown to range between eight and 23.3 months and usually require between 16 and 20 daily treatments.

• Dogs treated with CyberKnife for nasal tumors (carcinomas, adenocarcinomas and sarcomas) have comparable median survivals to dogs treated with conventional defi nitive radiation therapy. Preliminary data has shown median survivals of approximately one year with little or none of the morbidity typically associated with conventional radiation schemes. With the high accuracy of Cyberknife radiosurgery beams, structures including the eyes and brain can be avoided, thus eliminating both short term and any late term irreversible side effects from the radiation. The typical reversible short term side effects seen with conventional radiation in this region include mucositis to the oral and nasal mucous membranes and desquamation of the skin. The late term effects of radiation therapy to this region can include cataracts, rhinitis and tissue necrosis. These side effects can be typically avoided with CyberKnife radiosurgery.

• Other common tumors in veterinary medicine that have been treated with stereotactic radiosurgery include primary bone tumors of both the appendicular and axial skeleton. Osteosarcomas of the limb in non-amputation candidates have been treated with radiosurgery, and median survival times have ranged from 255 days to 572 days. This is much better than the one-year survival time using the current standard of care of amputation and chemotherapy. Fracture repair of a bone with an active tumor in a dog with advanced osteosarcoma is not usually pursued, so amputation or humane euthanasia is recommended. However, with a limb that has undergone radiosurgery, the primary bone tumor should theoretically be controlled, and therefore, fracture fi xation and the possibility of normal bone healing can be expected. CyberKnife robotic radiosurgery may be a good defi nitive alternative for nonamputation candidates.

• Other tumors that have been treated with radiosurgery include transitional cell carcinomas of the urethra in dogs where survivals ranged between 81 and 860 days; nonsurgical vaccine-associated sarcomas in cats where the median progression free intervals are over 432 days; and canine multilobular osteochondrosarcomas, which produced median survivals of approximately 252 days. The fi eld of radiosurgery is fairly new but is rapidly developing in veterinary medicine. With advanced technology such as stereotactic radiosurgery with CyberKnife, it is now possible to pursue a defi nitive therapy option for our patients, with little to no side effects or morbidity.

Dr. Jarred Lyons has been board-certified by the American College of Veterinary Radiology since 2007. He received his veterinary doctorate at UC Davis, completed a one-year surgical and internal medicine internship, and went on to complete a radiation oncology residency at North Carolina State University. He currently practices in the Los Angeles area and is one of the few veterinary radiation oncologists in the world to offer CyberKnife robotic radiosurgery.