July 2007

CyberKnife Radiosurgery at St. John’s
By Alan Scarrow, MD, JD, Chairman, St. John's Neurosurgery

With the August 2005 opening of the St. John’s Radiosurgery Center (SJRC), St. John’s joined a growing number of hospitals and health systems throughout the world by offering a relatively new and innovative form of treatment called radiosurgery. 

Since its opening, the SRC team has treated over 200 area patients with pathologies including metastatic brain and spine tumors, lung cancer, liver tumors, kidney cancer, ovarian cancer, acoustic neuromas, meningiomas and trigeminal neuralgia. In this article we will describe what radiosurgery is and how use of the CyberKnife at the SJRC places St. John’s at the forefront of contemporary management of patients with a variety of neoplastic, functional, and vascular disorders.

Traditionally, the term ‘surgery’ has been defined by most people with a rather strict and mechanical definition. For most of us that word invokes images of a bright, sterile room with physicians, nurses and technicians in hats, masks and gowns using knives and other sharp instruments to cut, remove, implant, and suture patients back to health. Yet the application of some ‘modern tools’ of surgery makes that traditional visual image seem somewhat archaic. 

For example today many surgeons use lasers, radiofrequency, heat, chemicals (e.g. alcohol, botulinin toxin, or chymopapain) or radiation to achieve similar results as conventional knives, retractors, suction and silk might be expected to attain. This change in technology has required many surgical specialties to redefine what ‘surgery’ really means. Now we might think of surgery more as the manipulation of an organ or tissue to achieve a specific purpose. This manipulation requires energy that may be supplied by mechanical (by simply moving an instrument), light (lasers), thermal (radiofrequency or heat), chemical, or radiation means.  This expanded definition of surgery more accurately reflects the contemporary therapies available to many surgeons.

Amongst these contemporary therapies is stereotactic radiosurgery (SRS). ‘Stereotactic’ is a Greek word meaning ‘movement in space’ and is used in this case to signify the use of three-dimensional coordinates to locate small targets within the body. ‘Radiosurgery’ is a manufactured word that is intended to describe the use of precisely placed radiation energy to destroy a target within the body in a manner similar to what a surgeon would traditionally use mechanical energy to perform. SRS is a distinct discipline that utilizes externally generated ionizing radiation in certain cases to inactivate or eradicate defined targets without the need to make an incision. The target is defined by high resolution stereotactic imaging (usually an MRI or CT scan). To assure quality of patient care the procedure involves a multidisciplinary team consisting of a surgeon, radiation oncologist, and medical physicist. 

SRS typically is performed in a single session but can be performed in a limited number of sessions, up to a maximum of five. Technologies that are used to perform SRS include linear accelerators, particle beam accelerators and multisource Cobalt 60 units. In order to enhance precision, various devices such as the CyberKnife may incorporate robotics and real time imaging that adds further accuracy to the delivery of the radiation. Accuracy of CyberKnife treatment from beginning to end, i.e. from imaging of the lesion to the actual delivery of radiation anywhere in the body, is documented at 0.9 mm or less.

Tissues treated with SRS respond differently that conventional radiation therapy. In addition to the cellular destruction induced by radiation on the nuclear level, SRS induces vascular changes in the form of thrombosis, fibrinoid necrosis of the vessel walls, hyaline degeneration and hemorrhage.  These vascular changes occur over a prolonged latency period of 12-14 moths after treatment and may largely explain the improved response that highly vascular lesions such as renal cell metastasis, melanoma and vascular malformations have in response to SRS versus conventional radiation therapy. Some speculate that based on animal studies, vascular cell apoptosis occurs as an early event and helps in destruction of tumor blood supply.

Because SRS was invented and adopted early by neurosurgeons, most early applications of SRS were central nervous system (CNS) pathologies. There are 3 primary targets for SRS in the CNS. First, ‘normal’ brain may be targeted to destroy areas thought to be associated with abnormal neurological function such as the root entry zone of the trigeminal nerve in patients with trigeminal neuralgia or portions of the thalamus in patients with Parkinson’s disease, essential tremor and multiple sclerosis tremor. Similarly SRS for epilepsy has also shown to be effective by destroying the portion of the ‘normal’ brain shown to be epileptogenic on functional imaging studies. Second, ‘malformed’ brain may be targeted such as with arteriovenous malformations (AVMs) or cavernous malformations. Third, ‘neoplastic’ areas of the CNS and surrounding tissue may be targeted such as metastatic tumors, meningiomas, schwannomas, neuromas, and occasionally primary brain tumors.

Despite this early pattern of SRS application in the CNS, by far the greatest growth in SRS is its use in patients with lung, liver, pancreas, renal, bone, and prostate tumors. For precisely the same reasons that SRS has become so popular with neurosurgeons and their patients (i.e. high efficacy, low morbidity, ease of use), SRS outside the CNS is becoming more common amongst thoracic surgeons, general surgeons, and urologists. The underlying questions preventing widespread application of SRS outside the CNS are beginning to be answered.  Specifically data continues to emerge that tumors outside the CNS treated with SRS tend to respond in a similar manner (and in the case of lung cancer often better) to tumors inside the CNS and equally important that SRS outside the CNS can be delivered safely and accurately. 

As an example, Dr. Frank Schmidt, cardiothoracic surgeon at St. John’s, has treated dozens of lung tumor patients at SJRC who previously would have had very few treatment options (with significant morbidity) because of the location of the tumor in the lung. 

The future of SRS looks very promising. Currently, researchers at a number of institutions are developing radiation sensitizers that will make tumor tissue more susceptible to SRS. Likewise, a number of tissue protectants are being investigated so that healthy tissue exposed to radiation can be protected from the potentially deleterious aspects of radiation. In addition, new applications for SRS continue to be reported with small ‘lesions’ being created at carefully placed portions of the brain to help control such mental health diseases such as obsessive-compulsive disorder, depression and chronic pain.

We encourage you to visit us at the SJRC and learn more about the capability of the CyberKnife and SRS for your patients. Please don’t hesitate to contact us at 417-820-9365 to discuss whether the CyberKnife may be a treatment option for one of your patients.

Read more about the CyberKnife