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1 Author's Accepted Manuscript Dose Conversion Coefficients for Icrp110 Voxel Phantom in the Geant4 Monte Carlo Code M.C. Martins, T.P.V. Cordeiro, A.X. Silva, D. Souza-Santos, P.P. Queiroz-Filho, J.G. Hunt PII: DOI: Reference: To appear in: S X(13) RPC6049 Radiation Physics and Chemistry Received date: 8 October 2012 Accepted date: 23 April 2013 Cite this article as: M.C. Martins, T.P.V. Cordeiro, A.X. Silva, D. Souza-Santos, P. P. Queiroz-Filho, J.G. Hunt, Dose Conversion Coefficients for Icrp110 Voxel Phantom in the Geant4 Monte Carlo Code, Radiation Physics and Chemistry, http: //dx.doi.org/ /j.radphyschem This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

2 DOSE CONVERSION COEFFICIENTS FOR ICRP110 VOXEL PHANTOM IN THE GEANT4 MONTE CARLO CODE M. C. Martins 1 *, T. P. V. Cordeiro, A. X. Silva 1, D. Souza-Santos 2, P. P. Queiroz-Filho 2 and J. G. Hunt 2 1 Universidade Federal do Rio de Janeiro (UFRJ), Programa de Engenharia Nuclear (PEN); Av. Horácio Macedo, 2030, Bloco G - Sala Centro de Tecnologia Cidade Universitária, Ilha do Fundão, CEP Rio de Janeiro, RJ maximiano@gmail.com 2 Instituto de Radioproteção e Dosimetria (IRD);Serviço de Monitoração Externa (SEMEX) Av. Salvador Allende s/n Jacarepaguá - CEP Rio de Janeiro RJ The reference adult male voxel phantom recommended by International Commission on Radiological Protection nº 110 was implemented in the Geant4 Monte Carlo code. Geant4 was used to calculate dose conversion coefficients (DCCs) expressed as dose deposited in organs per air kerma for photons, electrons and neutrons in the Annals of the ICRP. In this work the AP and PA irradiation geometries of the ICRP male phantom were simulated for the purpose of benchmarking the Geant4 code. Monoenergetic photons were simulated between 15 kev and 10 MeV and the results were compared with ICRP 110, the VMC Monte Carlo code and the literature data available, presenting good agreement. 1. INTRODUCTION Dose deposition in human tissue due to exposure to ionizing radiation cannot be directly measured (Stadtmann, 2001). Dose Quantities in Radiation Protection and Dosemeter Calibration. Radiation Protection Dosimetry. Anthropomorphic mathematical phantoms (ICRU, 1992) are usually coupled to radiation transport codes for this evaluation. Several

3 Monte Carlo codes are available such as GEANT4 (Agostinelli, et al, 2003), MCNPX (Briesmeister, 2000), EGSnrc (Nelson, et al 1985). These codes are able to estimate the radiation protection quantities dose equivalent in tissue and effective dose by implementing the mathematical phantoms in their structure. The results of the simulation are usually expressed by Dose Conversion Coefficients (DCC) that link a measurable quantity like particle fluence to tissue dose (Schlattl, et al.,2007). Anthropomorphic mathematical phantoms appeared a few decades ago, starting with the Medical Internal Radiation Dose Committee (MIRD) phantom (Snyder, et al., 1978) which is a set of quadratic curves made to adjust the dimensions and weight of the ICRP reference man. Mathematical phantoms that follow this kind of description are usually known as MIRD type phantoms. Voxel mathematical phantoms followed aiming at the description of a more realistic geometry of the human body (Caon, 2004). Those models are obtained by the segmentation of computer tomography (CT) or magnetic resonance (MRI) images. They are composed by millions of volume elements (voxels) arranged in a tri-dimensional grid, each voxel corresponding to a tissue. Tissues are identified by a scale of shades of gray and the knowledge of human anatomy (Zubal, et al. 2001) in a process known as segmentation. After a voxel tissue is identified, it receives an integer code. Examples of voxel phantoms are MAX/FAX (Kramer, et al., 2006), NORMAN, KORMAN, VIP-Man, Visible Man (VisibleHuman, 2013) and the phantoms available online at the Yale University home page (Zubal, et al. 2001). The International Commission on Radiation Protection (ICRP) in its publication 110 (ICRP, 2009) presented its voxel phantoms of the reference adult man and woman. These models are made from medical images of real people, adapted to data presented in ICRP publication 89 (ICRP, 2002). The masses of organs in both models were adjusted to ICRP data.

4 ICRP 110 Phantom (Male) This work uses the ICRP male voxel phantom (ICRP, 2009). It was made from CT images of a 38 year old male individual, 176 cm tall and with a mass of 70 kg, to be compared with 176 cm height and 70 kg mass of the reference man. The original data set are 220 CT slices, each one with 256 x 256 pixels. Each pixel measured mm 3. A total of 122 tissues were segmented, 67 of which are bones or groups of bones. Not all of the organs and tissues that were later identified in the ICRP revision of anatomical data (ICRP, 2002) are present in the male phantom. Table 1 show some features of this phantom. Table 1. ICRP 110 male phantom features Property ICRP110 Male Phantom Mass (kg) 73 Heigh t(m) 1.76 Number of voxels 1,946,375 Slice Thickness (voxel height, mm) 8 Voxel in-plane (x,y) resolution (mm) Voxel Volume (mm 3 ) Number of columns 254 Number of rows 127 Number of slices 220 GEANT4 and VMC In this work we use the Monte Carlo codes Geant4 and VMC. Geant4 (GEometry And Tracking) (Agostinelli, et al., 2003.) is a simulation toolkit freely distributed by the European Centre for Nuclear Research (CERN) to describe the passage of radiation through matter. The Visual Monte Carlo code, VMC, was developed at the Brazilian Institute for Radiation

5 Protection and Dosimetry (IRD) (Hunt et al. 2004a) with the specific goal of simulating the passage of radiation through voxel phantoms. Initially it was based in the Yale phantom VoxTiss8 but it was updated to the ICRP phantoms. VMC allows the transport of photons emitted by a point source, a radioactive cloud or contaminated soil. The available energies are from 20 kev to 1.5 MeV. It only considers the Compton and Photoelectric effects in the calculations. The code has been benchmarked against EGSnrc and validated against TLD measurements (Hunt, et al. 2004a, 2004b). 2. METHODOLOGY The simulation code was written within the framework of Geant4, version 9.4.p02. The interaction processes chosen for photons and electrons are the Compton scattering, photoelectric effect, pair production, multiple scattering, ionization and bremsstrahlung, using the following Geant4 classes: G4ComptonScattering; G4GammaConversion; G4PhotoElectricEffect; G4eMultipleScattering; G4eIonisation; G4eBremsstrahlung; G4eplusAnnihilation; Voxel phantoms are implemented in Geant4 by use of its nested parameterization structure, defined in class G4PVParameterised. The electron cut off chosen was 20 kev. Air kerma to dose conversion coefficients (DCC) were obtained by simulating a plane parallel beam of monoenergetic photons, in the energy range of 15 kev to 10 MeV. The incident kerma was calculated by means of the ICRP 74 conversion coefficients of air kerma per unit fluence for monoenergetic photons. The deposited energy for each voxel was obtained and summed for all voxels belonging to each tissue or organ. Results were compared with the references (ICRP,

6 2009; Schlattl and Zankl 2007). The Visual Monte Carlo (VMC) code was also used to compare results for DCC's. The same irradiation configuration was simulated in the energy range of 20 kev to 1.5 MeV, the maximum energy allowed by the code. Electrons are not transported by VMC. 3. RESULTS The implementation of the ICRP110 male phantom in Geant4 is shown in Figure 1 on the center slice. Figure 2 shows the same phantom in the PA irradiation condition, the lines are photons paths in simulation. Figure 1. Slice cuts through the ICRP110 male phantom

7 Figure 2. ICRP Male Phantom AP irradiation geometry. Organ doses conversion coefficients are shown in figures 3-6. Results are compared with ICRP 110 (ICRP, 2009; Schlattl, Zankl 2007), and VMC. Figure 3. Dose Conversion Coefficients for Stomach AP irradiation geometry

8 Figure 4. Dose Conversion Coefficients for Lungs AP irradiation geometry Figure 5. Dose Conversion Coefficients for Colon AP irradiation geometry

9 Figure 6. Dose Conversion Coefficients for Stomach PA irradiation geometry Figure 7. Dose Conversion Coefficients for Oesophagus PA irradiation geometry

10 4. CONCLUSION Air kerma to organ dose conversion coefficients were obtained with Geant4 and VMC in the range of 15 kev to 10 MeV. Results obtained with both codes agree well with the ICRP reference from 30 kev to 2 MeV. Results obtained with Geant4 also agree with the reference in the extended range of 10 MeV which is not reached by VMC. Both codes are considered adequate for radiation protection purposes and dose calculation in voxel phantoms. REFERENCES 1. Agostinelli S., J. Allison, K. Amako, et al, Geant4 - a simulation toolkit. Nuclear Instruments and Methods in Physics Research. 506, Briesmeister J. F., MCNPTM - a general Monte Carlo N-particle transport code, version 4c. Los Alamos National Laboratory, Los Alamos 3. Caon M., Voxel-based computational models of real human anatomy: a review. Radiat Environ Biophys. l42, Hunt J. G., et al. 2004a. The Validation of Organ Dose Calculations Using Voxels Phantoms and Monte Carlo Methods Applied to Point and Water Immersion Sources. Radiation Protection Dosimetry Vol. 108 No 1 pp ; 5. Hunt, J. G., et al. 2004b. Voxel phantoms and Monte Carlo methods applied to internal and external dose calculations. (Proc. 11th International Congress of the International Radiation Protection Association, Madrid), IRPA - 11 Proceedings and Abstracts, ICRP, Basic Anatomical and Physiological Data for Use in Radiological Protection Against External Radiation: Reference Values ICRP Publication 89 (Oxford: Pergamon). Ann ICRP 32(3-4) 7. ICRP, Recommendations of the International Commission on Radiological Protection ICRP Publication 103 (Oxford: Pergamon). Ann ICRP 37(2-4) 8. ICRP, Adult Reference Computational Phantoms. ICRP Publication 110. Ann. ICRP 39 (2). 9. ICRU, Phantoms and Computational Models in Therapy, Diagnosis and Protection. Report 48, Bethesda, MD.

11 10. Kramer R, et al., 2006, MAX06 and FAX06: update of two adult human phantoms for radiation protection dosimetry, Phys. Med. Biol. 51 (2006) Nelson W. R., Hirayama H. and Rogers D. W. O., The EGS4 code system. Report 265, Stanford, CA.(Stanford, CA: Stanford Linear Accelerator Center) 12. Schlattl H., Zankl M., Mand Petoussi-Henss, Organ dose conversion coefficients for voxel models of the reference male and female from idealized photon exposures Phys. Med. Biol. 52, Snyder W. S., Ford M. R. and Warner G. G., Estimates of absorbed fractions for monoenergetic photon sources uniformly distributed in various organs of a heterogeneous phantom MIRD. Pamphlet 5 revised. Society of Nuclear Medicine, New York. 14. Stadtmann, H., Dose Quantities in Radiation Protection and Dosemeter Calibration. Radiation Protection Dosimetry. 96, Visible Human, 2013 (Acessed on 2013, Jan 20), Homepage : Zubal I G, et al High resolution, MRI-based, segmented, computerized head phantom The Zubal Phantom Data, Voxel-Based Anthropomorphic Phantoms Highlights Monte Carlo codes Geant4 and VMC were used to simulate the ICRP110 male voxel phantom Geant4 was used to calculate organ dose conversion coefficients for photons AP and PA irradiation geometries were simulated for benchmarking with the ICRP male phantom Geant4 results between 15 kev - 10 MeV present good agreement with published results

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