Medical Physics / A pencil beam algorithm for magnetic resonance image-guided proton therapy

Purpose The feasibility of magnetic resonance image (MRI)based proton therapy is based, among several other factors, on the implementation of appropriate extensions on current dose calculation methods. This work aims to develop a pencil beam algorithm (PBA) for dose calculation of proton beams within magnetic field regions of up to 3 T. Methods Monte Carlo (MC) simulations using the GATE 7.1/GEANT4.9.4p02 toolkit were performed to generate calibration and benchmarking data for the PBA. Dose distributions from proton beams in the clinical required energy range 60250 MeV impinging on a 400 400 400 mm3 water phantom and transverse magnetic fields ranging from(VLID)341767

Commissioning a beam line for MR-guided particle therapy assisted by in silico methods

Background: Radiation therapy is continuously moving towards more precise dose delivery. The combination of online MR imaging and particle therapy, for example, radiation therapy using protons or carbon ions, could enable the next level of precision in radiotherapy. In particle therapy, research towards a combination of MR and particle therapy is well underway, but still far from clinical systems. The combination of high magnetic fields with particle therapy delivery poses several challenges for treatment planning, treatment workflow, dose delivery, and dosimetry. Purpose: To present a workflow for commissioning of a light ion beam line with an integrated dipole magnet to perform MR-guided particle therapy (MRgPT) research, producing not only basic beam data but also magnetic field maps for accurate dose calculation. Accurate dose calculation in magnetic field environments requires high-quality magnetic field maps to compensate for magnetic-field-dependent trajectory changes and dose perturbations. Methods: The research beam line at MedAustron was coupled with a resistive dipole magnet positioned at the isocenter. Beam data were measured for proton and carbon ions with and without an applied magnetic field of 1 T. Laterally integrated depth-dose curves (IDC) as well as beam profiles were measured in water while beam trajectories were measured in air. Based on manufacturer data, an in silico model of the magnet was created, allowing to extract high-quality 3D magnetic field data. An existing GATE/Geant4 Monte Carlo (MC) model of the beam line was extended with the generated magnetic field data and benchmarked against experimental data. Results: A 3D magnetic field volume covering fringe fields until 50 mT was found to be sufficient for an accurate beam trajectory modeling. The effect on particle range retraction was found to be 2.3 and 0.3 mm for protons and carbon ions, respectively. Measured lateral beam offsets in water agreed within 0.4 and −0.5 mm with MC simulations for protons and carbon ions, respectively. Experimentally determined in-air beam trajectories agreed within 0.4 mm in the homogeneous magnetic field area. Conclusion: The presented approach based on in silico modeling and measurements allows to commission a beam line for MRgPT while providing benchmarking data for the magnetic field modeling, required for state-of-the art dose calculation methods