Monte Carlo computation of 3D distributions of stopping power ratios in light ion beam therapy using GATE‐RTion

Abstract

This paper presents a novel method for the calculation of three-dimensional (3D) Bragg-Gray water-to-detector stopping power ratio (s w,det ) distributions for proton and carbon ion beams. Methods: Contrary to previously published fluence-based calculations of the stopping power ratio, the s w,det calculation method used in this work is based on the specific way GATE/Geant4 scores the energy deposition. It only requires the use of the so-called DoseActor, as available in GATE, for the calculation of the s w,det at any point of a 3D dose distribution. The simulations are performed using GATE-RTion v1.0, a dedicated GATE release that was validated for the clinical use in light ion beam therapy. Results: The Bragg-Gray water-to-air stopping power ratio (s w,air ) was calculated for monoenergetic proton and carbon ion beams with the default stopping power data in GATE-RTion v1.0 and the new ICRU90 recommendation. The s w,air differences between the use of the default and the ICRU90 configuration were 0.6% and 5.4% at the physical range (R 80 -80% dose level in the distal dose falloff) for a 70 MeV proton beam and a 120 MeV/u carbon ion beam, respectively. For protons, the s w, det results for lithium fluoride, silicon, gadolinium oxysulfide, and the active layer material of EBT2 (radiochromic film) were compared with the literature and a reasonable agreement was found. For a real patient treatment plan, the 3D distributions of s w,det in proton beams were calculated. Conclusions: Our method was validated by comparison with available literature data. Its equivalence with Bragg-Gray cavity theory was demonstrated mathematically. The capability of GATE-RTion v1.0 for the s w,det calculation at any point of a 3D dose distribution for simple and complex proton and carbon ion plans was presented.

On the perturbation effect and LET dependence of beam quality correction factors in carbon ion beams

“…The quantity p dis was calculated by $${D}_{{\rm{air}}}/{D}_{{\rm{cav}}}$$, where D air is absorbed dose to a thin cylindrical air slab (1‐cm radius and 250 μm thickness), and D cav is the absorbed dose to the air cavity of the IC without any other subcomponents present. The p cav correction factor was not reported in this study as it is independent of the IC model/type and requires calculation of water‐to‐air stopping power ratios, which was outside the scope of this work and has been studied elsewhere for ICRU report 90 data 23,34 …”

“…The p cav correction factor was not reported in this study as it is independent of the IC model/type and requires calculation of water-to-air stopping power ratios, which was outside the scope of this work and has been studied elsewhere for ICRU report 90 data. 23,34…”

A high-resolution large-area detector for quality assurance in radiotherapy

“…To illustrate this phenomenon, www.nature.com/scientificreports/ we have selected two pertinent studies that effectively highlight the impact of different materials. A study 46 was conducted to investigate the water-to-detector stopping power ratio for the plateau region. Additionally, the influence of the quartz window on the Peakfinder was investigated through comprehensive studies conducted at Heidelberg 47 .…”

The OpenGATE ecosystem for Monte Carlo simulation in medical physics

“…Current hot topics in the field of proton and carbon ion therapy, such as variable proton Relative Biological Effectiveness (RBE) depending on Linear Energy Transfer (LET) [136] (see next sections), the influence of fragmentation spectra on carbon ion RBE [115], influence of new stopping power tables (e.g. ICRU90) for 3D dosimetric applications with protons and carbon ions [22] are fully supported by the Gate-RTion release.…”