Positron-Emission-Tomography for ion beam therapy (PT-PET)
At Helmholtz-Zentrum Dresden-Rossendorf the in-beam Positron-Emission-Tomography (PET) has been developed as a technology for the visualizatio of a radiation field in ion beam therapy. The objective of this method is the verification of the correct dose application to the target volume and the exclusion of an unwanted irradiation of healthy tissue.
The dedicated "BASTEI" PET system has been developed in the framework of the German Heavy Ion Tumor Therapy Project, which was carried out at the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt and the HZDR. Between 1997 and 2008, approximately 440 patients have been irradiated with carbon ions.
The method is based upon nuclear fragmentation, which occurs as a consequence of irradiation of tissue with beams of hydrogen, helium, lithium, carbon and oxygen. Fragmentation reactions can lead to the loss of a neutron of a nucleus. Thereby β+ radioactive nuclei, like 11C, 10C or 15O, are created. These nuclei decay by emission of a positron and and a neutrino. The positron is the antiparticle of the electron. It travels up to a few millimeters in the tissue and subsequently annihilates with an shell electron of an atom. In this process, the mass is transformed to energy and released in form of two quanta. These quanta have an energy of 511 keV and a relative angle of 180°. By means of oppositely placed detectors these photons can be detected. Since the energy is known, and the angle between the two quanta is 180°, from events that occur in a small time window, the so called coincidences, the source distribution can be reconstructed.
PET has originally be developed for functional imaging in the field of nuclear medicine. The application for irradiation verification comes with various special requirements.
Based upon the aforementioned BASTEI system, our groupworked on the topics listed below:
- 4D in-beam PET for moving tumors
- Assisted evaluation of the PET data
- Yield-based simulation
- Activity build-up for He and Li ions
Since 2014, at the OncoRay center a cyclotron is in operation which accelerates protons to an energy of 230 MeV. Compared to a carbon beam which was used during the project at GSI, the proton beam from the cyclotron shows a different time microstructure. Our goal is to develop a PET system which is able to perform in-beam PET measurements during proton beam application.