a-Si EPID Modeling in GATE for Monte Carlo Investigation on the Optical Properties of Gd₂O₂S:Tb and Lu₂SiO₅:Ce Scintillators

Abstract:

A detailed a-Si Electronic Portal Imaging Device (EPID) was implemented in GATE (Geant4 application for tomographic emission) toolkit for Monte Carlo simulations, employing the standard electromagnetic processes and optical photon processes. The composition of the scintillating material is varied using the conventional terbium-doped gadolinium oxysulfide phosphor (Gd₂O₂S:Tb) and cerium-doped lutetium oxyorthosilicate (Lu₂SiO₅:Ce) which is widely used in Positron Emission Tomography (PET) detectors due to its supremacy in aiding the detection of low-energy photons. It was found that the number of optical photons produced is higher when using the Lu₂SiO₅:Ce scintillator resulting in a slightly better signal-to-noise ratio (SNR). The scattering within the EPID components was also investigated where the majority of the detected secondary particles were created in the scintillator. The results also show that the copper plate layer of the EPID contributes to additional Compton electrons and bremsstrahlung and annihilation photons to the measurements in the scintillator and photodiode layer. The glass substrate, graphite plates, electronic components, and aluminum bottom cover are also found to contribute a huge fraction of backscattered particles to the measurements at the photodiode layer.

• Periodical: Materials Science Forum (Volume 1102)
• Pages: 133-139
• DOI: https://doi.org/10.4028/p-0LSvwa
• Online since: October 2023
• Authors: Dainna Recel S. Pamisa*, Catherine Therese J. Quiñones
• Keywords: EPID, GATE, Monte Carlo, Optical Photons, Scintillator

References

[1] W. Renner, K. Norton, and T. Holmes, A method of deconvolution of integrated electronic portal images to obtain incident fluence for dose reconstruction, J Appl Clin Med Phys 6 (2005) 22-39.

DOI: 10.1120/jacmp.2026.25359

[2] K. Chytyl-Prax K. Chytyk-Praznik, E. VanUytven, T. vanBeek, P. Greer, and B. McCurdy, Model-based prediction of portal dose images during patient treatment, Med Phys 40 (2013) 1-11.

DOI: 10.1118/1.4792203

[3] W. van Elmpt, S. Nijsten, B. Mijnheer, A. Dekker, and P. Lambin, The next step in patient-specific QA: 3D dose verification of conformal and intensity modulated RT based on EPID dosimetry and Monte Carlo dose calculations, Radiother Oncol 86 (2008) 86-92.

DOI: 10.1016/j.radonc.2007.11.007

[4] M. Wendling, L. McDermott, A. Mans, J. Sonke, M. van Herk, and B. Mijnheer, A simple backprojection algorithm for 3D in vivo EPID dosimetry of IMRT treatments, Med Phys 36 (2009) 3310-21.

DOI: 10.1118/1.3148482

[5] I. Olaciregui-Ruiz, S. Beddar, P. Greer, N. Jornet, B. McCurdy, G. Paiva-Fonseca, B. Mijnheer, and F. Verhaegen, In vivo dosimetry in external beam photon radiotherapy: Requirements and future directions for research, development, and clinical practice, Physics and Imaging in Radiation Oncology 15 (2020) 108-16.

DOI: 10.1016/j.phro.2020.08.003

[6] C. Yeboah and S. Pistorius, Monte Carlo studies of the exit photon spectra and dose to a metal/phosphor portal imaging screen, Med Phys 27 (2000) 330-39.

DOI: 10.1118/1.598835

[7] J. Siebers, J. Kim, L. Ko, P. Keall, and R. Mohan, Monte Carlo computation of dosimetric amorphous silicon electronic portal images, Med Phys 31 (2004) 2135-46.

DOI: 10.1118/1.1764392

[8] L. Parent, J. Seco, P. Evans, A. Fielding, and D. Dance, Monte Carlo modelling of a-Si EPID response: The effect of spectral variations with field size and position, Med Phys 33 (2006) 4527-40.

DOI: 10.1118/1.2369465

[9] D. Sarrut, M. Bardiès, N. Boussion, et al., A review of the use and potential of the GATE Monte Carlo simulation code for radiation therapy and dosimetry applications. Med Phys. 41 (2014).

DOI: 10.1118/1.4871617

[10] D. Sarrut et al, Advanced Monte Carlo simulations of emission tomography imaging systems with GATE, Phys Med Biol 66 (2021).

[11] S. Agostinelli, J. Allison,K. Amako, J. Apostolakis,H. Araujo,P. Arce, and et. al., GEANT4 - a simulation toolkit, Nuclear Instruments and Methods in Physics Research 506 (2003) 250-303.

[12] S. Blake, P. Vial, L. Holloway, P. Greer, A. McNamara, and Z. Kuncic, Characterization of optical transport effects on EPID dosimetry using Geant4, Med Phys 40 (2013) 1-14.

DOI: 10.1118/1.4794479

[13] Information on https://opengate.readthedocs.io