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With particle therapy, more and more patients around the world are benefiting from precise dose deposition in the tumor. Due to the characteristic depth dose distribution, however, hadron therapy is particularly susceptible to range inaccuracies. Particle range verification is the subject of current research, but not yet a clinical standard. To circumvent this problem, safety margins are currently being defined around the tumor volume, which nullify the potential precision of particle compared to conventional photon therapy. The use of the prompt gamma radiation resulting from the deceleration of hadrons in tissue for range verification is a promising approach here. At present, various methods exist (for example, prompt gamma-ray imaging, prompt gamma-ray spectroscopy, prompt gamma-ray timing, prompt gamma-ray peak integration), which attempt to obtain information regarding the range from the temporal and / or spatial distribution of these high-energy photons. However, all methods are based directly or indirectly on the results of particle transport calculations. But their results show significant discrepancies compared to the experimental data [1] - [7]. Photon production cross sections are particularly important for range verification with prompt gamma radiation, although there is hardly any experimental data for the clinically relevant isotopes to check and optimize the underlying models. The importance of prompt photon yields in clinical research was therefore also the subject of the 2nd ESTRO Physics Workshop Science and Development "Improving Range Accuracy in Particle Therapy" and will soon be emphasized again in a position paper of the society. At the University Proton Therapy Dresden, the prompt emission spectrum of homogeneous graphite targets of different thickness was determined by irradiation with 90, 150 and 226 MeV protons. The detector response of the CeBr3 scintillation detectors (placed below 55 °, 90 ° and 125 ° with respect to the beam axis) was determined by Geant 4 simulations and verified by measurements with radioactive emitters. The emission spectrum was then obtained by unfolding the detector response using two different deconvolution algorithms (gold deconvolution and spectrum stripping). Scattered protons, which were detected in a YAP / BGO-Phoswich detector below 35°, were used to determine the incident proton fluence. The yields thus obtained are in good agreement with the available experimental data. Bibliography [1] J. Berthold, Single Plane Compton Imaging for Range Verification in Proton Therapy - A Proof-of-Principle Study, Dresden: Technische Universität Dresden, 2018. [2] L. Kelleter, A. Wronska, J. Besuglow, A. Konefał, K. Laihem, J. Leidner und A. Magiera, „Spectroscopic study of prompt-gamma emission for range verification in proton therapy,“ Physica Med., Bd. 34, pp. 7-17, 2017. [3] M. Pinto, D. Dauvergne, N. Freud, J. Krimmer, J. Létang und E. Testa, „Assessment of Geant4 Prompt-Gamma Emission Yields in the Context of Proton Therapy Monitoring,“ Frontiers in Oncology, Bd. 6, 2016. [4] J. Jeyasugiththan und S. Peterson, „Evaluation of proton inelastic reaction models in Geant4 for prompt gamma production during proton radiotherapy,“ Phys. Med. Biol., Bd. 60, p. 7617–7635, 2015. [5] A. Schumann, J. Petzoldt, P. Dendooven, W. Enghardt, C. Golnik, F. Hueso-González, T. Kormoll, G. Pausch, K. Roemer und F. Fiedler, „Simulation and experimental verification of prompt gamma-ray emissions during proton irradiation,“ Phys. Med. Biol., Bd. 60, pp. 4197-4207, 2015. [6] J. Verburg, Reducing Range Uncertainty In Proton Thearpy, Eindhoven: Technische Universiteit Eindhoven, 2015. [7] J. Dudouet, D. Cussol, D. Durand und M. Labalme, „Benchmarking Geant4 nuclear models for hadron therapy with 95 MeV/nucleon carbon ions,“ Phys. Rev. C, Bd. 89, p. 054616, 2014. |
