Materials Research and Ion Therapy

There is a wide spectrum of unique studies concerned with the interaction of fast ions with materials:
This includes heavy-ion tracks in foils which - through subsequent chemical etching and galvanic replication - can produce micro pores or micro tubes with a wide range of applications; it also comprises calibration tests for cosmic ray measurements with the Alpha Magnetic Spectrometer (AMS) that were performed at SIS. The mission of AMS on the International Space Station (ISS) is to search for antimatter, in particular antinuclei in the universe.

Almost 30 years of fundamental research on the interaction of heavy ions with biological cells has lead to an important contribution of GSI to society in general: this is cancer therapy with heavy ion beams. The idea is to use the beam energy to destroy the DNA of the tumor cells and thereby to kill the tumor.

The main question is: how does one get the energy of the beam to the tumor without affecting the healthy tissue? Let us assume a tumor located at a depth of 12 cm e.g., in the brain. The state of the art in hospitals is to use photon beams which have the energy deposition profile shown by the blue line. Most of the energy is deposited in healthy tissue right after penetrating into the body. Some energy is deposited in the tumor but energy is also deposited behind the tumor again in healthy tissue.

Heavy-ions have a completely different energy deposition profile. Only little energy is deposited when the heavy ions enter the body; the beam energy can be tuned such that most of the energy is deposited at the position of the tumor; there is very little energy deposition behind the tumor. With heavy ions one thereby obtains a highly localized energy deposition with millimeter accuracy not only in depth but also in the lateral dimension.

For this, the so-called raster scan technique has been developed at GSI. With the help of two magnets the ion beam is steered over the tumor volume. By using the highest beam energy the remote part of the tumor is irradiated first and by lowering the energy one irradiates the less distant part of the tumor. In each plane the beam is moved over the area to be irradiated. In this way the irradiation pattern can be adjusted to any geometrical shape of the tumor, allowing rradiations in the vicinity of sensitive organs like the brain stem.

Heavy ions have a further advantage in therapy. They allow a quasi on-line supervision of the irradiation and one can precisely check where the heavy-ion beam is deposited. With the small amount of radioactivity induced by the irradiation one can perform a verification of the irradiation plan by the well-known positron emission tomography (PET), a standard technique used in many hospitals.

Patient treatments were started at GSI's medical unit in December 1997. More than 440 patients have been treated for tumors in the head or neck region. Subsequent monitoring of these patients over a five-year period revealed that the growth of the irradiated tumors was stopped in 75 to 90 percent of the patients, depending on the type of tumor. Side effects requiring treatment occurred only in very few cases.

Since 2009, this type of cancer therapy is in routine clinical use at the Heidelberg Ion-Beam Therapy Center (HIT). There, up to 1,300 patients can be treated annually. The accelerator facility and the technique for irradiation at HIT was developed and built from scientists and technicians of GSI. As part of a licensing agreement between GSI and Siemens AG more treatment centers after the model in Heidelberg are already under construction in Marburg and Kiel (both Germany).