Eye-cancer patients to benefit from LBL technician's ingenuity

March 11, 1994

By Jeffery Kahn, JBKahn@lbl.gov

Thanks in large part to the initiative and creativity of mechanical technician Mario Cepeda, a project to transfer LBL's eye cancer treatment program from the Bevatron to UC Davis is proceeding on schedule.

Although the closure of LBL's Bevatron in 1993 spelled the end of its radiotherapy program, much of the technology and knowhow pioneered by Lab researchers gradually is being transferred to hospitals and laboratories around the world. In the case of the Bevatron's ocular melanoma treatment program, efforts are underway to actually replicate the program at UC Davis using the 70 MeV Crocker Nuclear Laboratory cyclotron.

The new facility, expected to treat about 40 people a year, will open soon. LBL's involvement with the program includes designing and setting up the medical beamline, training personnel, and loaning a dosimetry and computer control system.

Treating an eye tumor with the Crocker Lab's proton beam can save not only lives but unlike conventional surgery, the eye itself. Treatment requires locking in place the patient's head and fixing its position so that the beam strikes the target tumor with absolute precision. Cepeda's contribution was to build a device to precisely position the patient during treatment.

The device, a high-tech chair that adjusts in many directions, can cost upwards of $250,000. Since limited funds existed to design a device, two principals in the project, radiation oncologist Joe Castro and AFRD physicist Tim Renner, turned to Cepeda.

"At times," says Renner, "we forget that there are very creative people throughout the Lab. Mario took it upon himself to design and build this chair. From an engineering standpoint, he had no model to work from, just his nine years experience working with us in the particle radiotherapy program. He built the entire patient positioner out of scavenged parts and pieces of aluminum."

Cepeda said he hand-milled the majority of the approximately 200 parts, purchasing only one part.

"To keep our costs down," he said, "nothing was motorized, although we use pressurized air for one movement. The cylinder that is part of the air drive came from an air-operated door at the Bevatron that is no longer needed. The bearings and shaft under the chair came from the Bevatron Biomed Facility overhead rail system." Another part was scavenged from salvage.

By necessity, Cepeda's device is an object of absolute precision. Tumors in the eye are extraordinarily tiny, typically one centimeter or less in diameter, and can be located next to the optic nerve. Sight is lost if, during treatment, the beam hits the optic nerve. So, the patient positioner must be able to move and hold the patient's head with a wiggle room of less than one millimeter.

For a patient, sitting in this chair at the business end of a proton beam can be a scary experience. Cepeda did what he could to minimize the trauma.

To help immobilize the head, the patient must close his or her mouth on a bite block. By locking the jaw in place, the head too becomes locked in place. But the patient also can suffer feelings of claustrophobia or a smothering sensation. Having observed this, Cepeda designed and machined a bite block that does its job less intrusively.

Cepeda said his past experience with radiotherapy patients helped in the design of the patient positioner.

"The Bevatron clinical program treated people with a number of different diseases, some located in the head, others in the body. I custom-made the devices that immobilized the area of the patient's body that was to be treated. Doing this, I got to see that people not only come in a range of sizes but they have different size heads. Our patient positioner has to work for all patients, and that's a challenge."

The chair was designed, engineered, and assembled based upon Cepeda's hand sketches, which he repeatedly modified and refined. To improve this process, Cepeda spent $6,000 of his own money to purchase a home computer and Computer Assisted Design (CAD) software.

"I'm transferring my sketches of the patient positioner to CAD," he says. "This will make it possible for clinics elsewhere to one day duplicate our device."