Interface PHYSIQUE - BIOLOGIE Geant4 Monte Carlo simulation @ CENBG ► Microdosimetry ► Geant4-DNA Sébastien Incerti on behalf of the Interface Physique Biology group CELLION Mid-Term meeting CENBG, February 3-5, 2006

Monte Carlo modeling at the heart of cellular irradiation ► At the cell scale → Comparison of cellular irradiation techniques (study of dose-effect response) → Microdosimetry using realistic geometries (from confocal microscopy and sub-micron ion beam analysis) ► At the DNA scale Modeling of fundamental processes (Physics, Chemistry, Biological damage…) after irradiation by light ions : the Geant4 DNA project and its extensions ► For innovative techniques at the sub-micron scale Ray-tracing at the nanometric scale : the AIFIRA nanobeam line

Published in IEEE Trans.Nucl.Sci.51, 1395-1401 (2004) Cellular irradiation setups with alpha particles Focused microbeam - CENBG 3.5 0.1 0.3 Object collimator Ø=5 µm (platinum) Diaphragm Ø=10 µm (platinum) Magnetic volume : 4 quadrupoles with fringing field Collimator Ø=10 µm (platinum) Gas detector (isobutane) Exit window (Si3N4) Ambient air Culture foil (polypropylene) Cells in KGM (water) Microscope slide (glass) 5374.93 569.965 830 176.326 1.5e-4 4e-3 3 0.07 Beam pipe (aluminium) Alpha beam Cell layer Macrobeam - Bruyères - CEA/SP2A 6 Extraction window ( Havar ) Ambient air Culture layer Mylar Cells in growing medium water 3.5e - 3 5e Alpha beam Gold foil 6865 Beam pipe (vacuum) 100 000 cells / 1.54 cm 2 from 0.9e-3 to 6e-3 Ambient air Culture layer (Mylar) Cells in growing medium (water) 40 500e-3 Alpha source 16 Alphas a emitter sources 238/239 Pu - CEA/SP2A Published in IEEE Trans.Nucl.Sci.51, 1395-1401 (2004)

Submitted to Radiation Protection and Dosimetry (2005) Hit and dose distribution within the cell population Microbeam CENBG Macrobeam CEA a emitters CEA 0.5 a/nucleus, 5 min 12 s 1 a/nucleus, 10 min 24 s 1.5 a/nucleus, 15 min 36 s Absorbed dose distribution within an elliptic nucleus for 3 MeV incident alphas. The dose reaches 0.4 ± 0.1 Gy / alpha. About 0.5 % of incident alphas crossing the culture foil hit neighbour cells. Percentage of hit nuclei within the ellipsoid cell population irradiated with the Pu alpha emitter through a mylar thickness of 0.9 µm for an irradiation time of 5 min 12 s (plain circles), 10 min 24 s (plain triangles) and 15 min 36 s (plain squares). The corresponding Poisson fits are shown. The mean for an irradiation time of 5 min 12 s (dashed line) reaches 0.5 alpha per nucleus and is proportional to the irradiation duration (dot line for 10 min 24 s and mean of 1.0 alpha per nucleus ; dot-dashed line for 15 min 36 s and mean of 1.5 alpha per nucleus). Percentage of hit nuclei within the parallelepiped cell population irradiated with the CEA/DPTA 9.3 MeV alpha macrobeam. The plain circles represent Geant4 predictions and the dashed curve shows the corresponding Poisson fit, with a mean equal to one. The plain triangles and the dotted curve correspond to a Poisson distribution of mean 2. For illustration, the other plain curves show Poisson fits for means ranging respectively from 3 to 10 Submitted to Radiation Protection and Dosimetry (2005)

3D cellular voxellized phantom for microdosimetry with Geant4 Cellular geometry history Box classical literature 3D cellular voxellized phantom for microdosimetry with Geant4 → realistic voxellized geometry : - position - density - chemical composition (ex. through STIM / PIXE / RBS) → cell components staining : nucleoli, mitochondria, … → Geant4 advanced example Ellipsoid CEA / DSV confocal microscopy Phantom 1 CENBG confocal microscopy Nucleus DNA staining (H2B-GFP) detail Phantom II CENBG confocal microscopy nucleus DNA (H2B-GFP) + cytoplasmic membrane (Phalloidin)

Geometry dependence Geometry depends on → delay after seeding → cellular cycle phase → cell line 3 MeV incident a - ~ 140 keV/µm when entering cytoplasm 4 h after seeding delta alpha 512x512x50 Polypropylene Dx = Dy = 0.65 µm Dz = 0.24 µm 64x64x100 Growing medium Ambient air 104 incident alphas 24 h after seeding Dx = Dy = 0.17 µm Dz = 0.33 µm 256x256x50

Monte Carlo modeling at the heart of cellular irradiation ► At the cell scale → Comparison of cellular irradiation techniques (dose-effect response) → Microdosimetry using realistic voxellized geometries (confocal microscopy and sub-micron ion beam analysis) ► At the DNA scale Modeling of fundamental processes (Physics, Chemistry, Biological damage…) after irradiation by light ions : the Geant4 DNA project and its extensions ► For innovative techniques at the sub-micron scale Ray-tracing at the nanometric scale : the AIFIRA nanobeam line

http://www.ge.infn.it/geant4/dna Geant4 DNA Simulation of Interactions of Radiation with Biological Systems at the Cellular and DNA Level Based on Partly funded by European collaboration between S. Chauvie, R. Cherubini, Z. Francis, S. Gerardi, S. Guatelli, G. Guerrieri, S. Incerti, B. Mascialino, G. Montarou, Ph. Moretto, P. Nieminen, M.G. Pia, M. Piergentili + biologists (E. Abbondandolo, G. Frosina, E. Giulotto et al.)

Geant4-DNA : scope Provide simulation capabilities to study the biological effects of radiation at multiple levels ► Macroscopic → already feasible with Geant4 → calculation of organ dose → in progress : develop. useful associated tools (ex. human analytical & voxel. phantoms) ► Cellular level → in progress : processes for cell survival → expected : cell geometries modelling ► DNA level → in progress : physics processes at the eV scale (direct effects) → expected : DNA modelling → expected : chemical processes for radical species production (indirect) → expected : DNA strand breaking, fragmentation (up to 10-6 s after irradiation) Complexity of software, physics and biology addressed with an iterative and incremental software process Experimental validation Parallel development at all three levels (domain decomposition) Experimental validation Applications involve radiobiology, radiotherapy, space radioprotection, grid …

Multi-target single-hit TARGET THEORY models for cell survival Cellular level MODEL REFERENCE SURVIVAL FUNCTION VARIABLES Single-hit Lea (1955) S = exp(-D / D0 ) - Dose Multi-target single-hit S = 1- (1 - exp(-qD) )n - Dose - Probability to hit a target - Total number of targets - Number of targets hit Revised model S = exp(-q1D)  [ 1- (1- exp(-qn D))n ] Single-target multi-hit Single-target two-hits S= exp(-ßD2) Joiner & Johns S= exp(-αR [1 + ( αS / αR -1) e-D/Dc] D–ß D  ) ► Cell survival equations based on model dependent assumptions ► No assumption on Time Enzymatic repair of DNA E. L. Alpen « Radiation Biophysics », Academic Press, 2nd edition, San Diego, California USA, 1998

Lethal-potentially lethal MOLECULAR THEORY models for cell survival ► More sophisticated models Radiation action Linear-quadratic model Chadwick and Leenhouts (1981) S = exp(-p ( α D + ß D ) ) - Dose - Number of times a target is hit - Conditional probability function Dual radiation action Kellerer and Rossi (1971) S = S0 exp(- k (ξ D + D ) )  - Dose - Biological effectiveness factor - Fraction of dose related to SSBs and to DSBs - Unrestored fraction of bonds - Effectiveness factor Repair-misrepair Linear repair – quadratic misrepair Tobias et al. (1980)   S = exp-αD[1+(αDT/ε)]ε - Dose - Max time for repair - Linear repair constant - Quadratic repair constant - Probability for linear repair - Probability for quadratic repair Linear repair - misrepair S = exp-αD[1+(αD/ε)]εΦ Lethal-potentially lethal Curtis (1986)    S=exp[-NTOT[1+ NPL /[ε (1-e-εBAtr)] ]ε ] - Dose - Max time for repair - Number of lethal lesions - Number of potentially lethal lesions - Constants related to lesion processes - Constants related to repair processes Low dose approximation   S = exp(-ηACD) High dose approximation  - ln[ S(t)] = (ηAC + ηAB) D-ε ln[1 +(ηABD/ε)(1-exp(-εBA tr))] Linear-quadratic approximation - ln[ S(t)] = (ηAC + ηABexp(-εBAtr) ) D + (η2AB/2ε)(1-exp(-εBA tr)2 D2] E. L. Alpen « Radiation Biophysics », Academic Press, 2nd edition, San Diego, California USA, 1998

Submitted to Radiation Protection and Dosimetry (2005) Geant4-DNA : status of Physics processes DNA level Development of track structure modelling based low energy processes in liquid water Our goal is the development of step-by-step electromagnetic interactions for Electrons between 7 eV and 10 keV Protons, alphas and charge states between 1 keV and 10 MeV The processes considered are Elastic scattering (relevant only for electrons) Excitation of liquid water molecules Ionisation of liquid water molecules Charge exchange processes involving water molecules The software framework is based on a major design using policy based class design. Implementation and unit testing at advanced stage. Beta release for summer 2006. Long term plan is to have a reliable and maintainable framework not only for water processes, but also for other materials-dependent processes Submitted to Radiation Protection and Dosimetry (2005)

Aurora European Programme for the Exploration of the Solar System   Aurora European Programme for the Exploration of the Solar System The objective of the Aurora Programme is first to formulate and then to implement a European long-term plan for the robotic and human exploration of solar system bodies holding promise for traces of life. Shielding Human phantom

Monte Carlo modeling at the heart of cellular irradiation ► At the cell scale → Comparison of cellular irradiation techniques (dose-effect response) → Microdosimetry using realistic voxellized geometries (confocal microscopy and sub-micron ion beam analysis) ► At the DNA scale Modeling of fundamental processes (Physics, Chemistry, Biological damage…) after irradiation by light ions : the Geant4 DNA project and extensions ► For innovative techniques at the sub-micron scale Ray-tracing at the nanometric scale : the AIFIRA nanobeam line

Ray-tracing for the AIFIRA nanobeam line DOUBLET TRIPLET Electrostatic deflection 4565 5000 OM50 OM50 Diaphragm Object collimator Diaphragm 3150 400 40 400 40 250 Image plan Switching magnet X 90° analysis magnet 90° 300 100 11° 100 two stages : doublet + triplet high demagnifications : 65 in X, 100 in Y intermediate focus intermediate working distance of 30 cm long working image distance of 25 cm 60 nm x 80 nm Singletron incident beam Intermediate image Image < 50 nm FWHM STIM Object 5 µm in diameter Ray-tracing with Geant4 → Validation of Geant4 for ray-tracing at the sub-micrometric scale for the microbeam community ( G4 vs TRAX, Zgoubi, TRANSPORT) → Precise description of magnetic fringing fields in quadrupoles → Computation of system intrinsic and parasitic aberrations → Investigation of multiple scattering at very low pressure → Precise alignement (grid shadow) External envelope Experimental validation Published in Nucl.Instrum.Meth.B231, 76-85 (2005) Nucl.Instrum.Meth.B210, 92-97 (2003)

Conclusions and perspectives Three interconnected domains of expertise Ion beam techniques Geant4 Monte Carlo Cellular biology Single-ion microbeam line + STIM, PIXE, RBS with a sub-micron resolution (AIFIRA nanobeam line) Microdosimetry on realistic voxellised cellular geometries - High resolution 3D confocal imaging - cell components staining Single-ion microbeam line Simulation of fundamental interactions at the DNA level ► Geant4-DNA - Cell survival rates - Cell damage marking and quantification (SSBs, DSBs, fragments…) Nanobeam line dev. Ray-tracing in a high demagnification quadrupole system -

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Macroscopic level Anthropomorphic phantoms Development of anthropomorphic phantom models for Geant4 evaluate dose deposited in critical organs radiation protection studies in the space environment Original approach facilitated by the OO technology analytical and voxel phantoms in the same simulation environment Relevant to other fields, not only space radiation protection total body irradiation (radiotherapy)