Feasibility study of 4D-online monitoring of density gradients induced by lung cancer treatment using carbon ions

Claire-Anne Reidel ¹ Enrico Pierobon ² Felix Horst ^1,3 Levana Gesson ^1,4 Athena Paz ¹ Christian Graeff ^1,5 Timo Steinberger ¹ Klemens Zink ^6,7 Matthias Witt ^6,7 Yannick Senger ⁷ Christian Finck ⁴ Marie Vanstalle ⁴ Chiara La Tessa ² Marco Durante ^1,8,9 Uli Weber ¹ Christoph Schuy ^1*

• ¹ GSI Helmholtzzentrum für Schwerionenforschung GmbH, Biophysics Department, Darmstadt, Hesse, Germany
• ² Trento Institute for Fundamental Physics and Applications, University of Trento, Trento, Trentino-Alto Adige/Südtirol, Italy
• ³ Institute of Radiooncology – OncoRay, Helmholtz Center Dresden-Rossendorf, Helmholtz Association of German Research Centres (HZ), Dresden, Lower Saxony, Germany
• ⁴ UMR7178 Institut pluridisciplinaire Hubert Curien (IPHC), Strasbourg, Alsace, France
• ⁵ Department of Electrical Engineering and Information Technology, Darmstadt University of Technology, Darmstadt, Hesse, Germany
• ⁶ Institute of Medical Physics and Radiation Protection, THM University of Applied Sciences, Giessen, Germany
• ⁷ Marburg Ion Beam Therapy Center, University Hospital Giessen, Marburg, Germany
• ⁸ Institut für Physik Kondensierter Materie, Technische Universität Darmstadt, Darmstadt, Hesse, Germany
• ⁹ Department of Physics Ettore Pancini, Polytechnic and Basic Sciences School, University of Naples Federico II, Napoli, Campania, Italy

Tumor motion is a major challenge for scanned ion-beam therapy. In the case of lung tumors, strong under-and overdosage can be induced due to the high density gradients between the tumor-and bone tissues compared to lung tissues. This work proposes a non-invasive concept for 4D monitoring of high density gradients in carbon ion beam therapy, by detecting charged fragments. The method implements CMOS particle trackers that are used to reconstruct the fragment vertices, which define the emission points of nuclear interactions between the primary carbon ions and the patient tissues. A 3D treatment plan was optimized to deliver 2 Gy to a static spherical target volume. The goodness of the method was assessed by comparing reconstructed vertices measured in two static cases to the ones in a non-compensated moving case with an amplitude of 20 mm. The measurements, performed at the Marburg Ion-Beam Therapy Center (MIT), showed promising results to assess the conformity of the delivered dose. In particular to measure overshoots induced by high density gradients due to motion with 83.0±1.5% and 14D-monitoring of density gradients in ion-beam therapy 92.0±1.5% reliability based on the ground truth provided by the time-resolved motor position and depending on the considered volume and the iso-energy layers.