Radiosurgery: Marriage of Human Expertise and Technology

By Leslie Bernstein

The surgical tray next to the operating table was draped with the usual sterile blue cloth, but its contents--three Allen screwdrivers and four medium-sized titanium bolts--until very recently would have baffled most neurosurgeons. But then, most neurosurgical teams don’t include a radiation oncologist and a medical physicist, and most don’t plot a course of surgery by programming a high-powered computer. In this case, the tools and team were in place to radiate a patient’s brain using a gamma knife. In operation since March, the gamma knife is the newest of several advanced radiosurgical instruments now available for treating patients at Columbia-Presbyterian Medical Center. With the gamma knife, the medical center has one of the nation’s most comprehensive radiosurgical programs, at one of the few medical centers anywhere that can provide both the professional expertise and the technologically advanced infrastructure required for radiosurgery. The gamma knife is “a delivery system that holds 201 cobalt sources in a spherical geometry that allows each one to be focused to a common point, so that they cross fire to an isocenter in the patient,” says Dr. Peter Schiff, chairman of radiation oncology. The instrument’s sci-fi aura comes from four 450-pound stainless steel helmets, or collimators, that look something like enormous colanders. The collimators allow radiation to be delivered with minimal exposure to surrounding tissue. Each has different-sized holes that range in size from 4mm to 18mm. The patient’s headframe is held onto the skull by small pins, and the entire headframe docks into the gamma knife by anchoring screws. Once the headframe is fixed to the collimator, the patient, who lies on a mechanical couch, is slowly moved into the gamma knife’s treatment area. Sometimes patients are treated with a single helmet, Dr. Schiff says, but more frequently a lesion may have more than one isocenter, and each requires treatment with a different helmet. “Placing a 20-ton gamma knife at an institution like this one, with formidable neurological surgery, neurology, imaging, and radiation oncology services, allows us to get the best opinions about treating various diseases, and then to offer the right therapy, whether it’s surgery by microvascular technique, ‘wand’ therapy, radiation using a linear accelerator, or the gamma knife,” says Dr. Steven Isaacson, associate professor of radiation oncology and otolaryngology/head and neck surgery. Dr. Isaacson codirects the gamma knife program with Dr. Michael Sisti, assistant professor of neurological surgery. When scans for a patient are completed, Dr. Isaacson rushes up to radiology with hard copies for a brief consultation with Dr. Alexander Khandji, associate professor of radiology, and Dr. John Pile-Spellman, professor of radiology. Meanwhile, the patient is transported to the all-new dedicated gamma knife suite, located in the basement of Babies & Children’s Hospital, where patients rest in individual bays that are comfortable and private. The suite is overseen by veteran nurse practitioner Jerry Lesser, who, together with Dr. Isaacson and Dr. Sisti, has had specialty training for the gamma knife. Once the radiologists confirm Dr. Isaacson’s impressions of the size, shape, and position of the lesion, Dr. Isaacson returns to the gamma knife suite’s computer room, where Dr. Sisti joins him. Thanks to the sophisticated fiberoptic network in place at CPMC, the MRI images are transferred to the gamma knife’s computer. Now the real work begins: Dr. Isaacson and Dr. Sisti plot the brain site to be treated. About half an hour later, they are almost ready to go and call on Dr. Robertus Mooij, a medical physicist, to “triple-check the physics and treatment protocol,” Dr. Isaacson says, before treating the patient. Actual treatment lasts anywhere from five to 45 minutes, then patients stay overnight in the Irving Center for Clinical Research. Almost all are discharged the morning after their treatment. From March 9, when the first gamma knife patient was treated, through mid-August, more than 80 patients had been treated with the new instrument, well on the way to surpassing the 100 patients projected for the first year. “One of the early criticisms of radiosurgery was that it was a technology in search of a disease,” Dr. Isaacson says. “Clearly, this is not the case.” The gamma knife has been used to treat patients with neuromas, skullbased cancers, primary brain tumors, cancers that metastasize from other sites to the brain, arteriovenous malformations, trigeminal neuralgias, and meningiomas. The gamma knife may be used to treat a variety of benign lesions. It also may have potential in treating parkinsonism, epilepsy, and such psychiatric disorders as obsessive/compulsive behavior. Complementing the gamma knife is intensity modulated radiation therapy, or IMRT. “This is a combination of hardware and software that works in tandem with our existing linear accelerators,” Dr. Schiff says. “It allows us to increase the dose of radiation without also increasing the risk of side effects associated with radiation treatment, so we’re able to reduce the risk of complications using this new technology.” The technology is difficult to explain, Dr. Schiff says. “The analogy I like to use is a checkerboard. Each square on the checkerboard is a window that can be opened or closed by computer control. The radiation oncologist defines a target tissue and surrounding normal tissue that may be at risk, and the computer programs a sequence of windows to be opened and closed.” Generating a treatment plan can take hours of computer time, with the computer sometimes running overnight. “IMRT gives an optimal dose distribution while respecting tolerances of normal tissues,” Dr. Schiff says. Like the gamma knife, IMRT requires close collaboration among radiation oncologists, radiologists, and medical physicists. Doctors hope IMRT will prove effective in treating prostate cancer and central nervous system tumors not suited for gamma knife treatment, and Dr. Schiff also sees it as having potential to treat esophageal and breast cancer. It is also being used to treat irregularly shaped tumors and was used recently to reduce the size of a heart tumor. “Two years ago, we probably wouldn’t even have attempted to treat a heart tumor, because too much radiation can damage the heart,” Dr. Schiff says. In this case, the medical team included a radiation oncologist, medical oncologist, and a thoracic heart surgeon. Another new operating system now available to neurosurgeons at P&S is the SurgiScope, made by the same company that manufactures the gamma knife. With its position sensor system and robotic microscope holder, the SurgiScope helps neurosurgeons with preoperative plans. It also is used during surgery to provide 3-D images of the surgical site that can be viewed from various angles and that are constantly updated throughout the procedure. “With the SurgiScope, we can directly integrate information from various imaging studies into a surgical procedure,” says Dr. Robert Solomon, chairman of neurological surgery. The system can accommodate any type of scan, including MRIs, CTs, and digital and MR angiography. It consists of image-handling software and a robotic microscope holder, which also can accommodate lasers, endoscopes, and other tools. Before surgery, the neurosurgeon can use it to locate the target point, optimal trajectory, and placement of the craniotomy. The surgeon also can test alternative approaches and examine surrounding tissue by using it in virtual surgery. When “real” surgery begins, the SurgiScope provides images of any structures along the surgical path, helping surgeons choose the safest, least invasive, and most direct approach to the site of the lesion. The surgeon also can instruct the instrument to zero in on a portion of an image that may warrant a closer look. The SurgiScope is useful for tumors, arteriovenous and other types of vascular malformations, and aneurysms. “Clearly, it facilitates our ability to operate on deep, hard-to-locate lesions,” Dr. Solomon says. In some cases, simpler versions of the SurgiScope can be used, for example, without the robotically controlled microscope. In other cases, the surgeon may use only a Freehand Viewing Wand, a pen-like pointing instrument that provides 3-D computerized images of any portion of the brain, using scanned MRI or other images. Like the SurgiScope, the wand assists with preoperative planning and guidance during surgery.

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