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

Image Guided Particle Therapy - what can we learn from conventional RT?

Meeting Abstract

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  • H. Nyström - The Skandion Clinic, Uppsala, Sweden

PTCOG 48. Meeting of the Particle Therapy Co-Operative Group. Heidelberg, 28.09.-03.10.2009. Düsseldorf: German Medical Science GMS Publishing House; 2009. Doc09ptcog153

DOI: 10.3205/09ptcog153, URN: urn:nbn:de:0183-09ptcog1539

Published: September 24, 2009

© 2009 Nyström.
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Outline

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Imaging to ensure the correct position of the patient and the target has become an integrated and natural part of radiotherapy over the last few years. Imaging can, however, be used to address different kind of issues and not all modes of imaging are equally adequate to do solve the problem. With the patient regarded as a static, rigid body, substitutes for the target itself such as the body surface, bony landmarks or implanted markers will represent the position of the target. With, in a more realistic case, a breathing patient losing weight during the course of treatment, a completely different approach may be needed.

In conventional radiotherapy, the most used imaging modality is portal imaging, making imaging in beams eye view with the treatment beam, at the time of treatment possible. In PT, where the demands are much higher due to the sensitivity of the particle ranges, alternatives to this option must be found. Ideally such a system should be fast, possible to use during (or just prior to) the treatment and give detailed spatial information, including correct density information. In the context of breathing motion and respiratory gating, the imaging system must be possible to gate in the same manner as the treatment unit itself.

The use of the mid-ventilation CT frame, together with an intelligent design of margins, can successfully replace respiratory gating in many instances in conventional RT. The extent to which this approach can be applied in PT needs further investigations and is dependent on mode of beam delivery. In the case of lung tissue, however, density variations due to breathing, but also as an interfractional base line variation, calls for a more advanced imaging approach.

Looking at respiratory gating, the interfraction displacement, or motion, is most often of the same order of magnitude, or larger than the intrafractional motion. Any IGPT strategy must hence be able to address not only issues like base line shifts but also different breathing patterns on different treatment days. Adequate breathing coaching, combined with a relevant respiration monitoring is a prerequisite for successful gating. In the case of lung treatment, an imaging modality such as CT or CBCT that can reveal density information needs to be repeated during the course of treatment.