gms | German Medical Science

48th Meeting of the Particle Therapy Co-Operative Group

Particle Therapy Co-Operative Group (PTCOG)

28.09. - 03.10.2009, Heidelberg

RippleCompensator for Scanning Particle Therapy

Meeting Abstract

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  • M. Arnold - Universitätsklinikum Gießen und Marburg GmbH, Marburg
  • J. Farr - Westdeutsches Protonentherapiezentrum Essen gGmbH (WPE), Essen

PTCOG 48. Meeting of the Particle Therapy Co-Operative Group. Heidelberg, 28.09.-03.10.2009. Düsseldorf: German Medical Science GMS Publishing House; 2009. Doc09ptcog012

DOI: 10.3205/09ptcog012, URN: urn:nbn:de:0183-09ptcog0123

Published: September 24, 2009

© 2009 Arnold et al.
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Outline

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Background: In 2003 T. Sakae et al. (Sakae T, et al. Rev Sci Instr. 2003;74(3)) proposed a new method for conformal irradiation using multilayer energy filters for scanned particle beams. This multilayer energy filter is a combination of a ripple filter to create a SOBP and a compensator to shift SOBPs in depth. Using such filters allows irradiation of a complete field with a single scan at one fixed energy instead scanning of several energy layers. This suggests that irradiation time may be able to be reduced significantly in comparison to dose layer stacking delivery types. Hence a mitigation to the problem of applying scanned particle beams to moving targets can be provided. In this presentation the amount of time reduction is estimated for synchrotron and cyclotron based facilities. Additionally, ripple compensator construction and their effects on beam properties are discussed.

Material and methods: Scanned carbon beam treatment plans are calculated by means of Syngo PT planning/Siemens, scanned proton beam plans are generated using XiO/CMS. From these plans a matrix of position dependent SOBPs is extracted to calculate the patient and field specific ripple compensator. Prototype compensators are manufactured using a Invision XT 3-D Modeler (3D Systems Corp.) and other methods of rapid prototyping. The shape of the compensator is transformed to voxel geometry and copied into CT datasets. Finally back calculations based on the modified CT dataset are done for a single mono energetic layer. Influences of ripple compensator to beam quality are studied using FLUKA MC simulations.

Results: During irradiation of scanned particle fields switching from one layer to the next is one of the most time consuming actions. This time is currently far above 1 second either for cyclotron and synchrotron based facilities. One field of a lung case calculated with XiO for protons contains e.g. 20 layers. Hence irradiation time is reduced by 20 seconds at least, further number of spot positions is reduced from 799 to 93, total scan path length is shrinked to less than 7% of original length. As highest energy level only is needed for irradiation through ripple compensator, higher fluences can be achieved which reduces irradiation time again.

Considering the Syngo PT plan for a lung case using carbon, number of energy layers is 20 again, spot positions can be reduced from 3444 to 792 while path length is resized to 13% of original length. Hence significant reductions of irradiation times can be expected for synchrotron of Univ. of Marburg currently under construction.

Conclusion: Ripple compensators can lead to significant reduction of irradiation time. Reduction of time improves robustness of plans to organ motion. Main applications are e.g. lung, liver and pancreas cases. Construction requires no more efforts than manufacturing of compensators and templates in passive scattering irradiation techniques.

Acknowledgement: Len Coutinho, Westdeutschesprotonentherapiezentrum Essen, for treatment planning a lung case.