Validation of Geant4 for silicon microdosimetry in heavy ion therapy

Authors

David Bolst, University of WollongongFollow
Susanna Guatelli, University of WollongongFollow
Linh T. Tran, University of WollongongFollow
Lachlan Chartier, University of WollongongFollow
Jeremy A. Davis, University of WollongongFollow
Giordano Biasi, University of WollongongFollow
Dale A. Prokopovich, University of WollongongFollow
Alex Pogossov, University of Wollongong
Mark I. Reinhard, ANSTO
Marco Petasecca, University of WollongongFollow
Michael L. F Lerch, University of WollongongFollow
N Matsufuji
M Povoli
A Summanwar
Angela Kok
Michael A. Jackson, University of WollongongFollow
Anatoly B. Rosenfeld, University of WollongongFollow

RIS ID

141646

Publication Details

Bolst, D., Guatelli, S., Tran, L. T., Chartier, L., Davis, J., Biasi, G., Prokopovich, D. A., Pogossov, A., Reinhard, M. I., Petasecca, M., Lerch, M. L. F., Matsufuji, N., Povoli, M., Summanwar, A., Kok, A., Jackson, M. & Rosenfeld, A. B. (2020). Validation of Geant4 for silicon microdosimetry in heavy ion therapy. Physics in medicine and biology, 65 (4), 045014.

Abstract

Microdosimetry is a particularly powerful method to estimate the relative biological effectiveness (RBE) of any mixed radiation field. This is particularly convenient for therapeutic heavy ion therapy (HIT) beams, referring to ions larger than protons, where the RBE of the beam can vary significantly along the Bragg curve. Additionally, due to the sharp dose gradients at the end of the Bragg peak (BP), or spread out BP, to make accurate measurements and estimations of the biological properties of a beam a high spatial resolution is required, less than a millimetre. This requirement makes silicon microdosimetry particularly attractive due to the thicknesses of the sensitive volumes commonly being  ∼10 [Formula: see text]m or less. Monte Carlo (MC) codes are widely used to study the complex mixed HIT radiation field as well as to model the response of novel microdosimeter detectors when irradiated with HIT beams. Therefore it is essential to validate MC codes against experimental measurements. This work compares measurements performed with a silicon microdosimeter in mono-energetic [Formula: see text], [Formula: see text] and [Formula: see text] ion beams of therapeutic energies, against simulation results calculated with the Geant4 toolkit. Experimental and simulation results were compared in terms of microdosimetric spectra (dose lineal energy, [Formula: see text]), the dose mean lineal energy, y  D and the RBE10, as estimated by the microdosimetric kinetic model (MKM). Overall Geant4 showed reasonable agreement with experimental measurements. Before the distal edge of the BP, simulation and experiment agreed within  ∼10% for y  D and  ∼2% for RBE10. Downstream of the BP less agreement was observed between simulation and experiment, particularly for the [Formula: see text] and [Formula: see text] beams. Simulation results downstream of the BP had lower values of y  D and RBE10 compared to the experiment due to a higher contribution from lighter fragments compared to heavier fragments.