14th Geant4 Users and Collaboration Workshop

Geant4-based studies to characterise the tissue-equivalence of SOI and diamond microdosimeter detectors, under development at CMRP.

15 Oct 2009, 17:10

20m

Room "Azzurra" (Laboratori Nazionali del Sud - INFN)

Oral presentation Users Workshop Users' Workshop Parallel Session III - Medical

Speaker

Dr S. Guatelli (CMRP, University of Wollongong, Australia)

Description

Silicon On Insulator (SOI) microdosimeters have been under investigation for the past ten years as a possible alternative to tissue equivalent gas counters for microdosimetric measurements in medical physics and radiation protection in earth labs, aviation and space, at Centre of Medical Radiation Physics, University of Wollongong. In the last 5-6 years, extensive Geant4-based simulation studies have been performed to characterise the novel SOI detector. This talk is meant (1) to be a review of the past Geant4-related activities in silicon microdosimetry and (2) to show current Geant4-studies in microdosimetry at CMRP.

Keymords

Silicon and diamond microdosimetry, tissue-equivalence, Geant4.

Summary

Silicon On Insulator (SOI) microdosimeters [1] have been under investigation for the past ten years as a possible alternative to tissue equivalent gas counters for microdosimetric measurements in medical physics and radiation protection in earth labs, aviation and space.
Extensive Geant4-based simulation studies have been performed at the CMRP to characterise the novel silicon detector in radiation fields of interest, for proton therapy and radiation protection [2-6]. The Geant4 capability for microdosimetry has been studied through an extensive validation activity [2-5], based on the comparison of experimental data and Geant4 simulation results. A review of the Geant4-based study on SOI microdosimeter concept will be presented at the workshop.
Currently at CMRP we are studying a novel microdosimeter concept, where diamond is used, as the sensitive detector material rather than silicon because of its improved tissue-equivalence [7].
Geant4 simulations are currently being performed to characterise the tissue equivalence of this new detector, for proton therapy. First results will be shown at the workshop.
In the Geant4 simulation experimental set-up, the incident proton beam is generated isotropically on a sphere with radius 10 mm. The energy of the incident proton beam corresponds to the energy of the beam at the beginning, raising curve and Bragg peak position, of a 150 MeV proton therapy beam. The diamond sensitive detector is a sphere with diameter 10m, set in the outer sphere with radius 10 mm. The physics processes were chosen based on the study by Zacharatou Jarlskog and Paganetti [8]. The result of the simulation is the energy deposition per event in the sensitive detector, deriving from the interaction of both primary and secondary particles. Simulations are performed with water and diamond as material of the sensitive detector, to (1) quantify differences in the energy deposition spectra and to (2) eventually identify a methodology to convert microdosimetric spectra obtained in diamond to water.
The same Geant4 simulation set-up is adopted in a second current project in microdosimetry, aimed to study the tissue-equivalence of phantoms, commonly used in protontherapy facilities. In this case the energy deposition spectra obtained in silicon sensitive volume are compared when they are placed in different tissues and phantom materials. Differences in the chemical composition lead to variation in the contribution of delta electrons and nuclear recoils to the normalised energy deposition spectra. First results of this project will be shown as well.

[1] A. L. Ziebell, et al., “A novel cylindrical Silicon-on-Insulator microdosimeter for the characterisation of deep space radiation environments”, IEEE Trans. Nucl. Sci., vol. 56(3), pp. 1637-1641, 2009.
[2] A. J. Wroe, et al., “Microdosimetry simulations of solar protons within a spacecraft”, IEEE Trans. Nucl. Sci., vol. 52, no. 6, pp. 2591-2596, 2005.
[3] A. B. Rosenfeld, et al.“Analysis of inelastic interactions for therapeutic proton beams using Monte Carlo simulation”, IEEE Trans. Nucl. Sci, vol. 51, no. 6, pp. 3019-3025, 2004.
[4] A. Rosenfeld, et al., “Method of Monte Carlo simulation verification in hadrontherapy with non-tissue equivalent detectors”, Rad. Prot. Dosim., vol. 119, pp. 487-490, 2006.
[5] D. A. Prokopovich, et al. , “SOI microdosimetry for mixed field radiation protection”, Rad. Meas., vol. 43, pp. 1054-1058, 2008.
[6] S. Guatelli, et al., " Tissue Equivalence Correction in Silicon Microdosimetry for Protons Characteristic of the LEO Space Environment", IEEE Trans. Nucl. Sci. , vol. 55 (6), pp. 3407-3413, 2008
[7] B. Planskoy, “Evaluation of diamond radiation dosemeters,” Phys. Med. Biol, vol. 25, no. 3, pp. 519–532, 1980.
[8] C. Zacharatou Jarlskog, and H. Paganetti, “Physics Settings for Using the Geant4 Toolkit in Proton Therapy,” IEEE Trans. Nucl. Sci., vol. 55, no. 3, pp. 1018-1025, 2008.

Presentation materials

Slides

Guatelli_silicon_microdosimetry_G4Workshop.pdf

Guatelli_silicon_microdosimetry_G4Workshop.ppt