Calculation of the Beam-Modulation Effect of the Lung in Carbon Ion and Proton Therapy With Deterministic Pencil Beam Algorithms

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  • Toke Printz Ringbæk, Department of Radiotherapy and Radiation Oncology, University of Marburg, Department of Radiotherapy, University of Duisburg-Essen
  • ,
  • Alina Santiago, University of Marburg, University of Duisburg-Essen, Universitätsklinikum Giessen und Marburg, Standort Giessen
  • ,
  • Leszek Grzanka, The Henryk Niewodniczanski Institute of Nuclear Physics of the Polish Academy of Sciences
  • ,
  • Kilian Baumann, University of Marburg, University of Applied Science
  • ,
  • Veronika Flatten, University of Marburg, University of Applied Science
  • ,
  • Rita Engenhart-Cabillic, University of Marburg, Universitätsklinikum Giessen und Marburg, Standort Giessen
  • ,
  • Niels Bassler
  • Klemens Zink, Universitätsklinikum Giessen und Marburg, Standort Giessen, University of Applied Science
  • ,
  • Uli Weber, GSI Helmholtz Centre for Heavy Ion Research

Ion beams passing through lung tissue show more pronounced energy straggling than expected for solid materials of the same thickness. Energy straggling in active scanning particle therapy can enlarge the pencil beam Bragg peaks in-depth as well as displace them, deteriorating the dose coverage of a target within the lung. While this is not yet considered in any known treatment planning system, we implement a mathematical model to be used for treatment planning, using TRiP98, which relies on a deterministic pencil beam algorithm. Through a randomization process based on a continuous Poisson probability distribution, the HU values of lung voxels are replaced with a modified value in successive iterations. The beam-modulation effect of the lung can thus be taken into account in treatment planning by recalculating the dose n times for n randomized CTs using the raster scan file of a plan that was optimized on the nonmodulated CT. The evaluation follows by averaging the resulting n dose distributions and comparing to the corresponding nonmodulated dose distribution, attending at dosimetric indices and dose-volume histograms. In this work, the functionality of these routines was tested for proton and carbon ion plans for two selected lung cancer patient cases with deep-seated tumors, showing that, with existing standard tools, it is possible to calculate the beam-modulation effect of the lung in TRiP98 in a transparent way. Variable model parameters, such as modulation power, voxel size and density voxel selection range, were evaluated. Furthermore, a systematic study for spherical geometries in a lung tissue CT cube is presented to investigate general trends.

TidsskriftFrontiers in Physics
StatusUdgivet - 18 nov. 2020

Bibliografisk note

Funding Information:
The authors acknowledge the access to TRiP98, provided by M. Krämer and the GSI, and the cluster time at the PLGRID infrastructure in Krakow under Grant Number ccbmc7. The authors Ringbæk and Santiago acknowledge the support of M. Stuschke and S. Qamhiyeh from the Radiotherapy Department at Essen University Hospital. We thank Michelle Lis (GSI) for the linguistic improvement of the manuscript.

Funding Information:
The authors TR and AS acknowledge the financial support of the German fund for research “Deutsche Forschungsgemeinschaft” (DFG), case number SA 3085/1-1, Granted to AS. The study was also performed in the frame of FAIR Phase-0 supported by the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt (Germany).

Publisher Copyright:
© Copyright © 2020 Ringbaek, Santiago, Grzanka, Baumann, Flatten, Engenhart-Cabillic, Bassler, Zink and Weber.

Copyright 2020 Elsevier B.V., All rights reserved.

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