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

Range adaptation controlled by ion-optics for the beam tracking of moving targets

Meeting Abstract

  • N. Chaudhri - GSI Helmholtz Centre for Heavy Ion Research, Darmstadt
  • N. Saito - GSI Helmholtz Centre for Heavy Ion Research, Darmstadt
  • Chr. Bert - GSI Helmholtz Centre for Heavy Ion Research, Darmstadt
  • P. Steidl - GSI Helmholtz Centre for Heavy Ion Research, Darmstadt
  • B. Franzcak - GSI Helmholtz Centre for Heavy Ion Research, Darmstadt
  • M. Durante - GSI Helmholtz Centre for Heavy Ion Research, Darmstadt
  • E. Rietzel - Siemens Healthcare Sector, Particle Therapy, Erlangen
  • D. Schardt - GSI Helmholtz Centre for Heavy Ion Research, 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. Doc09ptcog039

DOI: 10.3205/09ptcog039, URN: urn:nbn:de:0183-09ptcog0396

Published: September 24, 2009

© 2009 Chaudhri et al.
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Outline

Text

Background: Beam tracking of a moving target with scanned charged particle beams requires fast adaptation of the particles' range in addition to lateral position adaptation [1]. We investigated an electromagnetically controlled range adaptation device that is installed inside the beam delivery system.

Method and material: The fast range adaptation method uses a small wedge-shaped degrader that is installed in-between two deflecting magnets inside the beam delivery system. The path of the beam through the wedge-shaped degrader can be controlled by ion-optical settings: The first magnet deflects the ion beam to a position on the degrader which corresponds to the required range adaptation. The second magnet shifts the modified beam back to the central axis of the beam line. Via the standard beam scanning system, the energy- modulated beam is then guided to the moving target and deposits dose at the correct range adapted position, i.e. the Bragg peak being located at the desired depth in tissue.

In contrast to range adaptation with the double-wedge systems at GSI [1] this principle does not involve any mechanical movements and therefore is expected to enable a very fast range adaptation (~1-10ms).

We tested this method experimentally as well as with Monte Carlo simulations using MOCADI (Schwab. PhD Thesis. Gießen: University (GSI Report 91-10).) each for the carbon ion therapy beam line at GSI. The setup included ramp-shaped and step-shaped degraders. Multi-wire position detectors were used to measure beam profiles before and behind the degrader and at the isocenter. The adapted particles range was measured using a range telescope (Schardt, et al. GSI Report 2008-19.).

Results: Horizontal beam deflections up to ±28 mm on the degrader and range shifts up to ~30 mm water equivalence (WE) were performed. Figure 1 [Fig. 1] shows the experimentally measured profiles for different beam positions on the ramp-shaped degrader (A) and the corresponding depth dose profiles (Bragg peaks) at isocenter (B). The difference between measured and expected range shifts was below 0.3 mm WE. The beam's lateral width measured at isocenter was between 5 and 12 mm full width at half maximum.

The measured results for range shifts and beam profiles agreed with the results obtained in the simulations.

Conclusion: The results demonstrate the feasibility of the proposed range adaptation method with respect to beam quality (lateral beam profile and shape of the Bragg peak).

Further investigations focus on optimization of the method (beam line) as well as the design of a control system for the proposed delivery method.


References

1.
Bert C, et al. Target motion tracking with a scanned particle beam. MedPhys. 2007;34(12):4768.