Online

ESTRO 2020

Session Item

Physics track: Dose measurement and dose calculation
9319
Poster
Physics
00:00 - 00:00
GATE/Geant4 as a Monte Carlo simulation toolkit for light ion beam dosimetry
Marta Bolsa Ferruz, France
PO-1370

Abstract

GATE/Geant4 as a Monte Carlo simulation toolkit for light ion beam dosimetry
Authors: Marta Bolsa-Ferruz.(EBG MedAustron GmbH, Medical Physics Department, Wiener Neustadt, Austria), Antonio Carlino.(EBG MedAustron GmbH, Medical Physics Department, Wiener Neustadt, Austria), Loic Grevillot.(EBG MedAustron GmbH, Medical Physics Department, Wiener Neustadt, Austria), Hugo Palmans.(EBG MedAustron GmbH, Medical Physics Department, Wiener Neustadt, Austria), Hugo Palmans.(National Physical Laboratory, Chemical- Medical and Environmental Science Department, Teddington, United Kingdom), Markus Stock.(EBG MedAustron GmbH, Medical Physics Department, Wiener Neustadt, Austria), Erik Traneus.(RaySearch Laboratories AB, Sales Particle Therapy, Stockholm, Sweden)
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Purpose or Objective

The growing interest in Light Ion Beam Therapy (LIBT) has fostered the efforts to improve the accuracy of ion beam dosimetry. Solid-state detectors are a good alternative to ionization chambers. To derive dose to water from the detector signal, the water-to-medium stopping power ratio (SPR) and the relative effectiveness (RE) of the dosimeter must be taken into account. Monte Carlo (MC) codes are essential tools for their determination since the complete particle spectra are required. Our aim is to compute these quantities in clinically relevant conditions using a fully commissioned clinical beam model and full clinical delivery sequences. This work intends to support end-to-end testing activities using alanine detectors, where the entire clinical workflow is executed using different phantoms.

Material and Methods

A numerical expression for calculating the water-to-medium SPR from the energy depositions scored by GateRT-ion MC platform and the water and medium mass stopping powers of the particle was developed. The water-to-medium SPR for protons and carbon ion beams was calculated as the ratio of the computed dose to water and the dose to medium (in water). A new tool for the computation of the RE was implemented in GATE. It makes use of the RE tables of the alanine detector as a function of energy for the different particle types [1]. The comparison of the dose distributions corrected by the RE and the data obtained with ionization chambers and alanine pellets during the dosimetric end-to-end tests activities of the proton beam lines at MedAustron Ion Therapy Center was performed [2]. RE results from GateRT-ion simulations were also compared with those from the RayStation v7.99.20 Treatment Planning System (TPS).

Results

The water-to-alanine SPR was computed in a water volume for different spread-out Bragg peaks (SOBP). A value of 1.02 for protons with a decrease of 2% along the depth-dose curve was obtained. The RE distribution for a homogeneous dose distribution in water and in a homogeneous phantom was computed for alanine. A difference with RayStation TPS for protons and carbon ions of less than 1% was found up to the 80% distal range (Figure 1).



Figure 1. Relative Effectiveness of alanine calculated with GATE and RaySearch TPS for a proton SOBP.

Conclusion

The capabilities of GateRT-ion for the determination of the water-to-medium SPR have been demonstrated. The method was shown to be equivalent to the Bragg cavity theory. The validation of the RE calculation in clinically realistic fields for protons and carbon ion beams was performed in this work. A good agreement was obtained in comparison with the RE implementation available in RayStation TPS.

References

[1] HERRMANN, R., Diss. PhD thesis, Aarhus University, Denmark (2012).

[2] CARLINO, A., et al., Physics in Medicine & Biology 63.5 (2018): 055001.