Heavy-ion cancer therapy
GSI is the birthplace of a new form of cancer treatment. This development was the result of many years of research in conjunction with GSI’s large ion-beam accelerator system.
To date, ion-beam radiotherapy has been used to treat more than 400 patients for tumors in the head or neck region. The advantage of this new treatment modality is that the ion beam selectively damages tumor tissues while sparing the surrounding healthy tissues.
Targeting cancer cells
The object of radiotherapy in oncology is to destroy tumor cells while sparing surrounding, healthy tissues. This requires maximizing the physical dose as well as the biological effectiveness in the tumor while minimizing them in healthy tissues. Accelerated ions meet these objectives far better than the commonly used X-rays.
Physical dose distribution
As an X-ray beam penetrates the body, the dose is at a maximum just beneath the skin and then decreases progressively at greater depths until the "remnant beam” emerges on the far side. Ions, on the other hand, penetrate into the body only to a specific depth, which depends on the speed of the ions. The dose along that route is low. But the dose reaches a sharp peak in the small—pinhead-sized—tissue volume in which the ions come to a stop. By controlling the speed of the ions, the depth at which this dose maximum occurs can be located precisely within the tumor. The dose in healthy tissue remains very small.
At the cellular level, the goal of radiotherapy is to cause irreparable damage to the genetic material of the cancer cells, ultimately causing their destruction. The biological effectiveness of ion radiation in introducing genetic damage into the cancer cells is significantly greater than that of X-rays. As a result, it is possible to achieve much greater tumor damage at a given physical dose without causing additional damage to healthy tissues.
Therapy: effective, well-tolerated and safe
To fully exploit the advantages of the carbon beam, the treatment planning as well as the therapeutic procedure itself are performed with the utmost precision. The pursuit of this objective led to the development of innovative new methods at GSI.
Biologically optimized treatment planning
To enhance the precision of treatment planning, GSI developed a model for calculating the biological effectiveness of carbon ions in different tissues. This, in combination with the physical dose distribution, allows the computation of the biologically effective radiation dose for each point in the tumor.
Precisely tumor-conformant irradiation
The raster-scan method developed at GSI allows the carbon beam to precisely and selectively scan the tumor volume. To this end, the speed of the ions—and consequently their penetration depth—is controlled by varying the energy level of the accelerator. In this manner the tumor is scanned layer by layer. Within each layer the scan is performed by deflecting the beam horizontally and vertically using magnets, much like the electron beam in a cathode ray tube. Even complex tumor shapes within the body can thus be uniformly irradiated with millimeterprecision. Damage to healthy tissue is minimized.
Online therapy monitoring
As they travel through tissues, a small number of carbon ions are transformed into a different carbon isotope. Each such event liberates two quanta of gamma radiation, which can be measured by special detectors. This process can be used to monitor the ion beam location within the patient during the treatment. Such online monitoring substantially enhances patient safety.