Implementation of a dose calculation algorithm based on Monte Carlo simulations for treatment planning towards MRI guided ion beam therapy

Abstract

Magnetic resonance guidance in particle therapy has the potential to improve the current performance of clinical workflows. However, the presence of magnetic fields challenges the current algorithms for treatment planning. To ensure proper dose calculations, compensation methods are required to guarantee that the maximum deposited energy of deflected beams lies in the target volume. In addition, proper modifications of the intrinsic dose calculation engines, accounting for magnetic fields, are needed. In this work, an algorithm for proton treatment planning in magnetic fields was implemented in a research treatment planning system (TPS), matRad. Setup-specific look up tables were generated using a validated MC model for a clinical proton beamline (62.4 -215.7 MeV) interacting with a dipole magnet (B = 0-1 T). The algorithm was successfully benchmarked against MC simulations in water, showing gamma index (2%/2mm) global pass rates higher than 96% for different plan configurations. Additionally, absorbed depth doses were compared with experimental measurements in water. Differences within 2% and 3.5% in the Bragg peak and entrance regions, respectively, were found. Finally, treatment plans were generated and optimized for magnetic field strengths of 0 and 1 T to assess the performance of the proposed model. Equivalent treatment plans and dose volume histograms were achieved, independently of the magnetic field strength. Differences lower than 1.5% for plan quality indicators (D 2% , D 50% , D 90% , V 95% and V 105% ) in water, a TG119 phantom and an exemplary prostate patient case were obtained. More complex treatment planning studies are foreseen to establish the limits of applicability of the proposed model.

Integrated MRI‐guided proton therapy planning: Accounting for the full MRI field in a perpendicular system

“…More recently, a detailed simulation and experimental study was conducted, which used a proton beamline, coupled with a small research dipole magnet in a perpendicular configuration. 19 This work demonstrated the feasibility of modified treatment planning to account for the localized near fringe and main 1 T magnetic field of a 12.5 cm pole gap dipole magnet. In their work, the particle source was located at 522 mm from the surface of the dosimetry phantom, and the magnetic field model covered a range up to 122 mm outside the phantom.…”

“…More recently, a detailed simulation and experimental study was conducted, which used a proton beamline, coupled with a small research dipole magnet in a perpendicular configuration 19 . This work demonstrated the feasibility of modified treatment planning to account for the localized near fringe and main 1 T magnetic field of a 12.5 cm pole gap dipole magnet.…”

An initial systematic study of the linear energy transfer distributions of a proton beam under a transverse magnetic field

“…The concept of MRintegrated proton therapy (MRiPT) and its design have been explored by several groups, [9][10][11] and feasibility studies have been conducted using both simulations 10 and experiments. [12][13][14][15] When analytical dose calculation models are concerned, analytical solutions to the deflected trajectory of a slowing-down proton beam in a magnetic field 16,17 and detailed modeling of the lateral beam profiles, including not only the Gaussian shape of the central core but also the low-dose tails, 18,19 are required as in the case without magnetic fields. 20,21 Unlike X-rays, where only the trajectories of secondary electrons are affected by the magnetic field, primary protons undergo deflections or rotations under transverse or longitudinal magnetic fields.…”

“…In a study conducted by Padilla-Cabal et al, 18 the low-dose tail of the lateral profile was modeled and validated using Monte Carlo simulation (MCS) and an experiment using a research dipole magnet. 19 They showed that the asymmetry of the low-dose tail between the inward and outward beam sides is more pronounced under a strong magnetic field. They also proposed two independent and exponential tailed functions, which successfully described the distorted lateral beam profiles.…”

“…They showed that a large energy difference of up to 20 MeV exists between the inward and outward beam sides because of the spectroscopic effects of the transverse magnetic field, although the lateral dose profile was mostly symmetrical and Gaussian curve shaped. In a study conducted by Padilla‐Cabal et al., 18 the low‐dose tail of the lateral profile was modeled and validated using Monte Carlo simulation (MCS) and an experiment using a research dipole magnet 19 . They showed that the asymmetry of the low‐dose tail between the inward and outward beam sides is more pronounced under a strong magnetic field.…”