Particle Therapy

There’s new hope for patients with inoperable tumors. A new treatment developed by Siemens in conjunction with the GSI Society for Heavy Ion Research shows promise. Based on irradiation with fast particles, the therapy destroys tumors permanently with minimum trauma.

It really doesn’t seem like a treatment at all—I get up and drive home as if nothing has happened. The only thing that reminds me of the reason for my daily visits to the research center is the mask that holds my head precisely in place for the ten-minute treatment." That’s how one patient describes his treatment at the Gesellschaft für Schwerionenforschung (Society for Heavy Ion Research, GSI) accelerator in Darmstadt, Germany. Suffering from a brain tumor that is too close to his optical nerves and brain stem for doctors to even contemplate surgical intervention, this patient, and thousands with similarly inoperable conditions, would normally be consigned to a bleak future.

But at GSI there’s a new, exceptionally precise treatment method that may offer an answer. "Particle therapy," which uses the properties of fast proton and ion beams, has already achieved initial clinical successes. Furthermore, a partnership between GSI and Siemens Medical Solutions is expected to set the stage for specialized clinical centers that guarantee patients a level of care that corresponds to their requirements. "The heightened release of energy by ions at the end of their trajectory through body tissue in conjunction with their high biological effectiveness makes them an outstanding tool for irradiating deep tumors," explains Dr. Thomas Haberer, technical project manager for therapy at GSI.

Accepted Therapy. GSI’s story began with basic research. But by 1997 its grid scanning process (box) was ready for testing. The following year, a long-term clinical study began with more than 250 patients at the National Cancer Research Center in Heidelberg, Germany. "Today," says Prof. Walter Henning, scientific director of GSI, "our therapy is accepted for some conditions, such as skull base tumors. But to fully develop the potential of this innovative technology, it would be advisable to conduct clinical tests on other tumorous areas as well."

With some tumors, conventional treatment methods—from surgical removal and chemotherapy to radiological treatment and combination therapies—come up against biological limits. These can be malignant growths that are difficult to reach, for example, or that lie near critical organs, as with brain tumors and tumors at the base of the skull. Another field of application comprises soft-tissue sarcomas and prostate carcinomas, which are surrounded by sensitive tissues. For these conditions, particle therapy is a new and effective course of treatment.

"The results of particle therapy have exceeded our expectations," says Dr. Jürgen Debus, medical director of Clinical Radiology in Heidelberg. "The tumors were destroyed quickly and permanently without damaging healthy tissues. We would now like to use this sort of radiation to treat other tumors and to help far more patients."

Particle therapy takes less time than conventional radiation therapies. 20 minutes of preparation and five to ten minutes of irradiation for an average of 20 days are enough to achieve marked remission of tumors and prevent the growth of new tumorous tissue. In addition, the treatment puts patients under a minimum amount of strain. Those who held jobs were able to continue working during therapy. Apart from minor swelling of mucous membranes and reddening of the skin, there were hardly any side-effects. These benefits are a result of the special biological effectiveness of ion beams (see box).

Pilot System. Using the insights acquired at the radiation treatment station in Darmstadt, GSI experts are designing a pilot system for the university clinic in Heidelberg. But unlike the GSI system, the new accelerator will be operated by a specially trained team of clinicians rather than by scientists. By 2006, the Heidelberg center is expected to have three radiation treatment stations accommodating roughly 1,000 patients per year. Two of the treatment stations will be similar to the radiation treatment station at GSI, and the third will be equipped with a rotatable beam-transport system. "This will allow ion beams to be focused on diseased tissue from any direction—a feature that makes it relatively easy to circumvent neighboring critical organs," explains Haberer.

All of the system’s components have already been individually tested in experiments at GSI. But the system’s structural limitations and economic requirements represent a new challenge. An area measuring 60 by 70 m will have to accommodate two ion sources, a linear accelerator only 5 m in length, a synchrotron with six magnets and a diameter of 20 m, and three treatment rooms.

In order to make this new tumor irradiation method accessible to a greater number of patients, Siemens Medical Solutions and GSI signed a partnership agreement in October 2003. Using GSI’s patent data, Siemens is developing a standardized and certified particle-therapy system for routine clinical use. In addition, Siemens will also be responsible for production and marketing. The company foresees that standardized components and modular-design systems will greatly simplify and accelerate the planning, startup and licensing of future radiation treatment facilities.

"With this commitment to particle therapy, we’re emphasizing our clear-cut intention to use innovative solutions to build on Siemens Medical Solutions’ leading market position in oncology," says Dr. Walter Folberth, project manager for particle therapy at Siemens. "Our customers are also increasingly demanding a provider of comprehensive solutions with medical expertise in oncology, diagnostic imaging and information technology integration for all work processes," he says.

Anja Stemmer

High Speed Tumor Treatment

GSI’s accelerator system (see illustration) and the planned system in Heidelberg are designed to make the most of the grid scanning process. Ions are created in a gas discharge and injected into a system consisting of a linear accelerator and a synchrotron ring. In the synchrotron, the particles move in a circular path at up to 50 % of the speed of light. The synchrotron provides therapy stations with a pulsed particle beam of a precisely defined energy, focus and intensity, delivering portions that are metered-out, so to speak. The energy level determines penetration depth; the intensity determines the irradiance; and the focus determines the decrease in dosage in the surrounding healthy tissue. These parameters can be changed in an instant.

Before treatment, a computer tomogram measures the tumor to an accuracy of about 1 mm. Treatment planners then divide up the tumor volume perpendicular to the beam axis, defining virtual sections 2 to 3 mm in thickness, which are then successively scanned with the ion beam. In the case of typical volumes of 0.5 l, the radiation parameters must be calculated for approximately 20,000 points. During treatment planning, a team of specialists selects the optimal settings from a pre-established library of focal characteristics and intensity levels, allowing precision treatment of even the most difficult tumors, such as those that have wrapped themselves around a healthy organ. (The  illustration at top left uses plexiglass disks to show how a torus is irradiated without affecting the center.)