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

An algorithm for optimizing beam angle configuration in particle therapy

Meeting Abstract

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  • G. Cabal - Department of Radiation Oncology, University Hospital of Heidelberg, Heidelberg, Germany
  • S. Luan - Department of Computer Science, University of New Mexico, Albuquerque, USA
  • O. Jäkel - Heidelberg Ion Beam Therapy Center, University Hospital of Heidelberg, Heidelberg, Germany

PTCOG 48. Meeting of the Particle Therapy Co-Operative Group. Heidelberg, 28.09.-03.10.2009. Düsseldorf: German Medical Science GMS Publishing House; 2009. Doc09ptcog033

DOI: 10.3205/09ptcog033, URN: urn:nbn:de:0183-09ptcog0337

Veröffentlicht: 24. September 2009

© 2009 Cabal et al.
Dieser Artikel ist ein Open Access-Artikel und steht unter den Creative Commons Lizenzbedingungen (http://creativecommons.org/licenses/by-nc-nd/3.0/deed.de). Er darf vervielfältigt, verbreitet und öffentlich zugänglich gemacht werden, vorausgesetzt dass Autor und Quelle genannt werden.


Gliederung

Text

Background: Beam angle selection is an important and still unsolved problem for particle therapy. In this work we develop a beam angle selection algorithm that takes into account PTV coverage, healthy tissue sparing (OAR) and plan robustness.

Materials: The goal of our optimization is to maximize the number of tumor voxels that can be treated with minimum violation of: (1) Avoid placing beam spots next to the critical regions along the beam path. (2) Beam path should avoid going along the boundary of density inhomogeneities. (3) Beam path should avoid high Z, high density regions, which tend to have higher CT uncertainties. (4) Beam path should avoid going through critical targets whenever possible. The objective function was optimized using a stochastic optimization algorithm. Once an optimal beam angle configuration was found, the final plan was optimized using an in-house treatment planning system for 2D studies whose dose calculation algorithm and optimization algorithm was taken from published work [1], [2].

Results: A skull base tumor was used to evaluate the beam angle selection algorithm. The patient model consisted of one CT slice with a tumor and three critical structures: brain stem, optic nerves and eyes.

We compared three different beam configurations: (1) Two opposing beams at 90 and 270 degrees clockwise. This configuration is common in facilities that have a fixed beam line. (2) Two oblique beams at 70 and 290 degrees. This configuration was suggested by a professional treatment planner. (3) Two oblique beams calculated using the proposed algorithm, which are roughly at 60 and 300 degrees.

For each beam configuration, a plan is calculated using our TPS with the same constraints. The optimized plans are then subject to set-up errors and CT-to-Ranges calibration uncertainties taken from published data [3], [4], [5].

The proposed algorithm remarkably improves the beam angle configuration of the plan in terms of quality and robustness.

Conclusions: A beam angle selection algorithm that optimizes plan quality and robustness was developed and tested in a 2D plan. Results encourage further work on a 3D implementation of our algorithm.


References

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Jäkel O, et al. Relation between carbon ion ranges and x-ray CT numbers. Med Phys. 2001;28(4):701-3.
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Lomax A. Intensity modulated proton therapy and its sensitivity to treatment uncertainties 1: the potential effects of calculational uncertainties. Phys Med Biol. 2008;53:1027-42.