Introducing a novel method for fast and accurate estimation and compensation of beam deflection in MR-integrated proton therapy


Introducing a novel method for fast and accurate estimation and compensation of beam deflection in MR-integrated proton therapy

Schellhammer, S. M.; Hoffmann, A. L.

Proton therapy is highly sensitive to anatomical variations due to steep dose gradients in proximity of the Bragg peak (BP). Magnetic resonance imaging (MRI) is a promising candidate to enable real-time tracking of such variations during treatment delivery with high spatial, temporal and contrast resolution and without ionizing radiation exposure. However, an MRI magnetic field applied during irradiation deflects the proton beam from its intended trajectory.
We present a numerical method for fast and accurate quantification and compensation of this effect. As compared to existing approaches, it features fewer approximations than analytical models and a strongly reduced computation time compared to Monte Carlo simulations. We use it to reconstruct the trajectory of a monoenergetic proton beam of energy E0 traversing a water phantom behind a 25 cm air gap inside a virtual MRI bore with a uniform transverse magnetic flux density B. We study the dislocation of the BP as function of E0 and B and introduce an optimization method to compensate for it.
The magnitude of BP dislocation ranges from 2 cm for E0=60 MeV and B=0.5 T up to 26 cm for E0=250 MeV and B=3.0 T. A unique solution exists for repositioning the BP by beam incidence angle and energy adjustment.
The predicted magnetic-field induced BP dislocation complies with results obtained by Monte Carlo methods and the model is more versatile than analytical methods. The proposed optimization of beam incidence angle and energy effectively repositions the BP to its intended location.

Keywords: proton therapy; image-guided radiotherapy; IGPT; magnetic resonance imaging; MR guidance; beam trajectory prediction

  • Poster
    55th Annual Conference of the Particle Therapy Co-operative Group (PTCOG 55), 22.-28.05.2016, Praha, Ceska republika
  • Poster
    10th HZDR PhD seminar, 02.-04.11.2015, Altenberg, Deutschland
  • Poster
    National Center for Radiation Oncology, 2nd Scientific Retreat, 14.-16.04.2016, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-23950
Publ.-Id: 23950