Real Virtuality

Stereolithography models facilitate pre-operative planning, helping surgeons cut operating time up to thirty percent. Patients benefit through fewer complications, quicker recoveries, and shorter hospital stays.

A concerned woman arrives at the hospital with an apple-sized tumor behind her ear. After a thorough diagnosis, doctors determine they must remove the tumor in order to ensure the patient's survival.

Traditionally, this complicated procedure would require the removal of a large portion of the skull, leaving a sizable area of the woman's brain exposed. How can the surgeons patch the hole in the shortest time with least risk of infection? Faced with this difficult challenge, surgeons turned to Dr. Paul D'Urso and Anatomics, aat the Queenslaand Manufacturing Institute (QMI), lead by Scott Loose, Chairman of the Queensland Manufacturing Institute. Since 1991, Dr. D'Urso has been championing the benefits of stereolithography (SL) in medical applications.

For years, the benefits of SL have been readily apparent in the manufacturing arena, with product diversity ranging from car engines to toys and cellular phones. At the QMI, however, D'Urso has put a human face on this technology. His work is not to speed products to market but to speed patients to recovery.

"Biomodeling" Process
In the case of the woman with the tumor, the conventional surgical method involves a cumbersome and inexact procedure. The surgeon must first uncover the tumor and remove it in the best manner possible. In order to plug the hole left behind, the surgeon molds methyl methacrylate, or "acrylic bog," into the shape of the hole. Unfortunately, the "bog" continually hardens, and, if the acrylic sets before the surgeon can successfully shape it, the surgeon must remove it and start again.

Through extensive research, D'Urso has developed a better procedure - a revolutionary, surgical technique he refers to as "biomodeling." D'Urso defines biomodeling as "the process of using radiant energy, CT or MRI data, to capture morphological data on a biological structure and the processing of such data by a computer to generate the code required to manufacture the structure on a rapid prototyping apparatus, more specifically a Stereolithography Apparatus (SLA)."

Using this technique, D'Urso quickly went to work. He received the CT data of the woman's skull from the hospital via ISDN (Integrated Digital Service Network) linkages, a data telephone connection to which any hospital could be similarly linked. He then processed the CT data through a specially written BioBuild software from Anatomics, separating the flesh and bone. This step was crucial to achieve optimal model accuracy. Using 3D Systems' software, D'Urso processed the data, generating the build file required to guide the SLA laser. D'Urso built a 3D model of the patient's skull and tumor on an SLA 250 at QMI using CIBATOOL SL 5177 resin. The resultant model accurately represented the CT data, which a tolerance of +/- 0.7mm.

Within twenty-four hours, the model was returned to the surgeons to be utilized several different ways, first as a diagnostic tool for pre-operative planning, to illustrate the operation to the patient, helping her better understand the surgical procedure, reducing her pre-operative anxiety. The surgeons rehearsed the actual surgical procedure on a second model. After removing the "tumor" from the model, the surgeons constructed an SL prototype of the implant which fit perfectly within the SLA biomodel of the skull. A mold was then made of the implant and cast as a finished product using a biomedical acrylic. Next, a cutting template was created to fit exactly over the tumor during surgery. Once ready, the surgeons "reflected" the patient's skin, placed the template over the tumor, and drew the exact area to be removed. Finally, the surgeons removed the actual tumor and placed the implant into the skull. An exact fit. A full recovery.

Reduced Time and Costs
D'Urso is especially pleased with this case because all four applications of SLA biomodeling were ideally used. As a tool for "rehearsal" surgery. As a tool to generate a custom-made implant before surgery. As a basis for a template to transfer the operative plan from model to patient. The surgeons estimated at least an hour timesavings over the traditional five-hour operation, a reduction in surgical time of over 20 percent. "SL models in the operating theater represent real virtuality," D'Urso maintains. "Instead of virtual reality, in which the surgeon must fool with goggles and gloves, the surgeon now has a three-dimensional model that he can feel and touch." No prior skills, computer or otherwise, are needed to use the models effectively because of their tactile, intuitive nature. "The technology itself is transparent to the surgeon, leaving him free to concentrate on the patient's needs and the success of the operation."

After over 200 operations, Australian surgeons estimate that the SLA biomodeling technique offers an average timesavings of up to 30 percent. One surgeon surmised that SL models cut four hours off a major cranio-facial operation, which usually took 12 to 16 hours. On average, surgeons feel the three-dimensional SL models are twice as helpful in the operating theater as traditional techniques such as X-rays and computer models, and most feel the utility of the SL model and implant easily justifies the production cost. With a reduction in operating time comes a reduction in blood loss, amount of anesthesia, and risk of infection. All of these factors lead to lower operating costs, which translate to real dollar savings for both patient and hospital.

Worthy of Insurance Coverage
D'Urso believes it is only a matter of time before private insurers see the wisdom in covering the cost of biomodeling for all types of surgery. Based on his scientific data, D'Urso hopes to persuade private insurers in Australia to cover the procedure. "The time savings from SL obviously pays for the surgical models, but there are more benefits to the patient, including a lesser chance of multiple surgeries due to rejection of the implant," D'Urso maintains. Scott Loose of QMI agrees. "The current medical applications of SL are only the tip of the iceberg. It is an area of manufacturing that we are only now starting to commercialize."

Once administrators learn the value of SL in medical applications, many hospitals may be operating an SLA on site. While the SLA biomodeling technique has proven beneficial in many types of surgery, the most important benefit is in human terms - in improvement of informed patient consent, in shorter operations and hospital stays, in minimized patient discomfort, and in increased surgical success.