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

Does delivery in the presence of organ motion

Meeting Abstract

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  • Chr. Bert - GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt

PTCOG 48. Meeting of the Particle Therapy Co-Operative Group. Heidelberg, 28.09.-03.10.2009. Düsseldorf: German Medical Science GMS Publishing House; 2009. Doc09ptcog019

DOI: 10.3205/09ptcog019, URN: urn:nbn:de:0183-09ptcog0190

Published: September 24, 2009

© 2009 Bert.
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Outline

Text

Treatment of targets that move during particle beam therapy requires dedicated mitigation techniques especially for tumors that move intra-fractionally (during irradiation) such as lung tumors. For scattered particle beams intra-fractionally moving tumors have been successfully treated for several years using dedicated planning target volumes (PTV) and/or gating. Gating is an irradiation technique that irradiates the target only in parts of the breathing cycle with little motion, typically at end-exhale. Motion is detected e.g. by the motion of the chest wall.

For scanned particle beams the interference of target motion and scanned beam causes under-dosage if only margins are used. Therefore no patients with intra-fractionally moving tumors have been treated with the conformal beam scanning technique. To allow irradiations of intra-fractionally moving tumors with scanned beams the motion mitigation techniques gating, beam tracking, and rescanning have been proposed and tested. Rescanning irradiates an appropriate PTV multiple times per fraction and relies on averaging of the interference effects. With a sufficient number of irradiations homogeneous coverage of the clinical target volume can be expected. Beam tracking adapts the position of the pencil beam based on the detected motion state of the target. Laterally the scanning system is used for beam adjustment; in depth a dedicated energy modulation system is required. Beam tracking is in principle capable to fully compensate target motion with PTVs that have to cover the residual uncertainties but not the full extent of the motion amplitude as for rescanning. Also gating has to be adapted in scanned beam therapy because residual interference effects can lead to under-dosage. An increased overlap of neighboring pencil beams or the combination with (phase-controlled) rescanning have been proposed for mitigation of this interference.

In the scope of the presentation the principles of the techniques mentioned above will be covered.