1 Department of Experimental Clinical Oncology, Faculty of Health Sciences, Aarhus University, Aarhus University2 Department of Physics and Astronomy, Science and Technology, Aarhus University3 Department of Physics and Astronomy, Science and Technology, Aarhus University
Antiprotons are interesting as a modality in radiation therapy for the following reasons: When fast antiprotons penetrate matter, they behave as protons. Well before the Bragg-peak, protons and antiprotons have near identical stopping powers exhibit equal radiobiology. But when the antiprotons come to rest at the Bragg-peak, they are captured by a nucleus and will quickly spiral into the core. When matter and antimatter meet, the restmass is converted into energy, thus releasing almost 2 GeV per antproton-proton annihilation. Most of this energy is carried away by pions. Some of these pions will disrupt the nucleus, producing fragments which deposit energy near the annihilation vertex. The Bragg-peak of the antiprotons is thus locally augmented with roughly 20-30 MeV per antproton. Apart of the gain in physical dose, also an increased relative biological effect has been observed, as some of the secondary particles from the antiproton annihilation exihibt high-LET properties. Additionally, the high energy pions are leaving the target with minimal interactions and can be detected external to the body providing a real time feedback on the exact location of the energy deposition. In recent years, we have carried out several experiments at CERN, where we investigated the dosimetry and radiobiology of an antiproton beam. Our findings indicate that the biological effect for antiprotons in the plateau region may be reduced by a factor of 4 for the same biological target dose in a spread out Bragg-peak, when comparing with protons. Currently we work on implemeting antiprotons in the treatment planning software TRiP, which is developed by GSI in Darmstadt for carbon ion treatment planning. We will here present the basic idea of antiproton radiotherapy and shows some key points of our research done so far.