- Enhanced Bragg Peak
The so called bragg peak, which is the peaked dose deposition at the end of the ion range is enhanced at heavy ions. Thus the ratio between the minimum dose in the entrance channel and the maximum dose in the peak is larger for heavy ions.
- Enhanced Biological Efficiency
Equal biological effects are achieved with heavy ions at a three times smaller dose. Thus, the total applied dose (in Gray) can be reduced significantly.
- Smaller Beam Radius
Protons (P) have a smaller mass and can be easier deflected by electronic interactions on their path through the human tissue. Therefore, independent from the initial radius after a certain penetration depht proton beams have always a larger radius of at least 5 mm. Heavy ion beams (C) can be focused onto a smaller radius of about 2 mm and keep this radius constant up to the end of the range. With such beams the surrounding of sensitive organs like the brain stamm can be treated with much higher precision.
- PET - Online Beam Monitoring
When have ions penetrate through the tissue a weak radiation is beeing emited which can be monitored by a special camera system called PET (positron emission tomography). With such a PET camera the beam position and the applied dose distribution can be checked during the treatment. Such an on-line monitoring is not possible with proton beams.
- Less Activation of the Accelerator
When high energetic protons are lost in the accelerator system or decelerated in the degrader, the surrounding technical devices gets activated. In case of technical failfunctions this activation doesn't inhibits a fast maintainance.
Advanced Treatment Technologies Developed for the GSI Therapy
- Active Energy (Range) Variation
The controle system developed at GSI is able to treat virtual accelerators with 255 energy steps. Each arbitrary energy step, which means a certain penetration depth in the patient, can be changed and requested from shot to shot. No degrader is used to decelerate the beam. No matter is required in the beam path. This is a technics that can only be realized with synchrotron accelerators and not with cyclotrons.
- Active Beam Radius Controle
The beam radius is controlled by active focusing elements, not by a passive collimation. The beam radii can be varried in seven steps in the range from 2 - 5 mm. By using active focusing elements instead of collimators the spot radius can be changed from shot to shot.
-Beam Intensity Variation
Fifteen different beam intensities can be chosen for the treatment. Each intensity step can be set from shot to shot.
- Raster Scanning
The GSI raster scanner moves the beam transversly over the tumor similar to a television tube. This technical development enables a precise irradiation of irregularly shaped tumors and an optimum saving of the surrounding healthy tissue. Furthermore a fast controle loop from the beam position monitors (MWPC) enables a correction and controle of the beam position (if necessary) during the treatment.
Technical Extensions of the GSI Accelerator
Facility for Cancer Therapy