Monte Carlo Modelling: a reliable and efficient tool in radiation dosimetry G. Gualdrini, P. Ferrari ENEA Radiation Protection Institute, Bologna (Italy) Contribution to the Italy in Japan 2011 initiative Science, Technology and Innovation
Foreward ENEA Radiation Protection Institute (IRP) is responsible of radiation protection within the eleven ENEA sites in Italy, where activities with associated radiation exposure risks are carried out. For this scope the Institute has set-up a series of experimental laboratories and facilities for research, development and service purposes. At the same time the Institute is present in a variety of international groups, committees and projects. In all these fields computational dosimetry is applied and Monte Carlo modeling plays a key role.
Monte Carlo simulations for radiation dosimetry Radiation protection issues imply a careful and reliable dosimetry which quality is guaranteed, besides by updated experimental techniques, also by an advanced Monte Carlo modeling capability. The activity has to be referred to the European and extra-european scientific community, to ease the exchange of knowledge to improve methodologies. Since some years ENEA IRP has been coordinating the Computational Dosimetry Working Group 6 within the European Dosimetry Group (EURADOS: www.eurados.org)
Photon personal dosimetry To characterize a dose-meter for photons it is necessary to irradiate it under standard conditions in a photon irradiation facility, using X-rays or gamma emitters. To optimize these reference beams and evaluate the response noise due to the effect of structural materials (source-collimator, walls, ceiling and floor), simulations based on Monte Carlo techniques allow separating the effects, which is difficult to afford experimentally. Personal photon dosimeters are to be calibrated on plastic phantoms reproducing in a simplified way the part of the body on which the dosimeter is worn.
CALIBRATION PHANTOMS A- 30x30x15 cm 3 slab phantom for chest (whole body dosimeters) B- Rod pillar phantom (wrist extremity dosimeters) C- Finger phantom (hand extremity dosimeters)
Monte Carlo modeling allows evaluating the overall photon radiation spectrum present on the phantom front face, due to both direct and backscattered components.
NEUTRON METROLOGY: IRP IRRADIATION ROOM Heavy water moderator Shadow cone Neutron sources bank
Monte Carlo evaluated neutron spectra at the Reference measurement point (direct + scattered contributions) Am-Be Heavy water moderated Cf Bare Cf Standard ISO neutron sources
Thermal neutron Assembly Sorgenti 241 Am-Be Cavità 1 F=17 cm L=20 cm Cavità 2 F=8.3 cm L=11 cm Cavità 3 F=12 cm L=15 cm Measurements of low energy neutrons (thermal region)
Thermal Neutron assembly (Monte Carlo model) Adapting the fracility for measurements on phantom outside the thermal column (violet) A- MODERATOR ASSEMBLY B- Calibration Phantom C- Personal Dosimeters D- Flattening Filter E- Thermal column after extraction of polyethylene module. F- Measurement cavity
Development of human models
Voxel models (a,c) much better reproduce the real anathomy than analytical ones (b) voxel analytical voxel (a) (b) (c)
CT VOXEL model development 1. Interpretation CT-DICOM matrices 2. image Segmentation 3. Transfer to Monte Carlo z voxel pixel z slice CT pixel m voxel
Details of NORMA05 NORMAN05: head Skull, carotids and thyroid
INTERNAL DOSIMETRY The radiation dose assessment from incorporated radionuclides is characterized by high complexity related to the accuracy of the metabolic model and of the calibration phantom adopted to mimic the real subject. BOMAB phantom to assess the activity of homogeneously distributed radionuclides
Need of human models for specific body parts CT scan model of a human skull and knee for bone-seeker radionuclides activity investigation
Modelling a molar tooth for retrospective dosimetry of radionuclides deposited in the tooth dentine
Naturally occurring radionuclides: Monte Carlo optimized detection of Radon ( 222 Rn) CR-39 Cavità 222 Rn Cavity walls daughter nuclides deposition The sensor is a plastic CR-39 slab 222 Rn (a 5.49 MeV) in equilibrium condition is a gas uniformly distributed in the detector cavity 222 Rn daughters 214 Po (a 7.69 MeV) and 218 Po (a 6 MeV) are in particulate form and deposit on the cavity walls. The emitted alpha particles were fully simulated with Monte Carlo to evaluate the response of the plastic sensor
Study of hand doses for enterventional radiology and cardiology X-ray examination of a patient during a heart catheterization
References References G. Gualdrini and P. Ferrari, A review of voxel model development and radiation protection applications at ENEA. Radiation Protection Dosimetry, Volume 140, 2010, 383-390 G. Gualdrini, F. Monteventi and B. Morelli, Determining the Photon Air Kerma Backscatter Factor Profiles for the ISO and ICRU Recommended Slab Phantoms:Comparison between LiF Measurements and Monte Carlo Calculations, Radiation Protection Dosimetry, Volume. 85, 1999, 71-74. G. Gualdrini, R. Bedogni, F. Monteventi, Developing a Thermal Neutron Irradiation System for the Calibration of Personal Dosemeters in Terms of Hp(10), Radiation Protection Dosimetry, Volume 110, 2004, 43-48 P. Ferrari and G. Gualdrini, NORMAN-05 conversion coefficients for monoenergetic neutrons below 20 MeV Radiation Measurements, Volume 43, 2008, 1515-1524 G. Gualdrini and P. Ferrari, Monte Carlo evaluated parameters for internal dosimetry Radiation Protection Dosimetry, Volume 125, 2007, 157-160 G. Gualdrini, P. Battisti, R. Biagini, P. De Felice, A. Fazio, P. Ferrari, Development and characterisation of a head calibration phantom for in vivo measurements of actinides. Applied Radiation and Isotopes volume 53, 2000, 387-393