An essential part in cancer radiotherapy, is to direct a sufficiently high dose towards the tumour, without damaging the surrounding tissue. Different techniques such as intensity modulated radiation therapy and proton therapy have been developed, in order to reduce the dose to the normal tissue. The stopping power of high-energetic antiprotons in tissue, is similar to that of protons. Most energy is lost per unit distance as the particle comes to rest, but when the antiprotons stops, each one will annihilate on a nuclei, releasing 1.9 GeV of energy. Most of this energy is carried away by pions, gamma rays and neutrons, but a part of the annihilation energy is still deposited locally as recoiling nuclear fragments with limited range. These fragments will also increase the relative biological effect at the annihilation vertex. We have masured the biological effect of an antiproton beam for the first time. The results indicate a 4 times lower biological effect in the plateau region of the depth-dose curve, compared to that of protons, for isoeffect in the spread-out peak region. Additional experiments were done in order to provide a sufficient data base for an existing treatment planning system to handle antiprotons. This will enable us to do treatment planning with antiprotons, and thereby bring us closer to answer the question of the potential clinical benefit of antiprotons.
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Dansk Selskab for Medicinsk Fysik (DSMF) - Symposium 2007