Probing the sub-disciplines: what do we know? what do we need to know? The physics The chemistry - Modelling

Transcription

1 Session 3: Probing the sub-disciplines: what do we know? what do we need to know? The physics The chemistry - Modelling Michael Dingfelder Department of Physics, East Carolina University Mailstop #563 Greenville, NC dingfelderm@ecu.edu.

2 Purpose of workshop First, the overall purpose of the workshop is to assemble an expert group to consider the question of whether current EU funded research is adequately addressing the effects of radiation quality on biological response to radiation of relevance to radiation protection. The core of the workshop will be discussion leading to recommendations for a strategic research agenda (and if possible a publication). The role of your presentation is to inform and stimulate the discussion. Session 3: This is a "horizon search". What are we missing? What new science has come up leading to new possible lines of research? But it must ALL relate to the fundamental question of whether radiation effects (of whatever type) may be qualitatively different as well as quantitatively different for different radiation qualities.

3 So what is missing?

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5 Introduction The Physics The Chemistry Modelling

6 Energy Deposition Trabecular bone Track Structure DNA Cells E dep E dep DNA (double helix) Base Pairs patterns clusters correlations Ion track segment

7 PARTRAC Biophysical Radiation Track Structure Simulation Code photons electrons protons alphas radiation transport track structure module radiation action effect module damage step by step location, deposited energy, kind of interaction water chemistry module production and transport of radiacals geometry module molecules chromatin... cells

8 Introduction Track structure and transport codes: an overview

9 Radiation Transport Transport codes: condensed history electromagnetic interaction nuclear interaction energy loss / nuclear fragmentation materials: atomic cross section data bases Track structure: event-by-event (detailed) description only electromagnetic interaction secondary electrons followed materials: liquid water DNA, proteins,

10 Charged particles: electrons protons, alphas, light ions: carbon, nitrogen, oxygen heavy ions: HZE particles Low-energy electrons: track ends damage / indirect effects Stages: physical chemical biological

11 Remarks: a) Energy loss Energy loss primary de/dx = E in - E out E in E out no secondary electrons considered Deposited energy (within volume) secondary electron transport considered b) Track structure simulations non-relativistic relativistic electrons heavy ions

12 Energy Deposition Trabecular bone Track Structure DNA Cells E dep E dep DNA (double helix) Base Pairs patterns clusters correlations Ion track segment

13 Time evolution physical chemical biological log (t) seconds Excitation Ionization Free Radical Reactions Enzymatic Reactions Repair Processes Early Effects Late Effects Carcinogenic

14 Time evolution physical stage From: H.G. Paretzke, in Kinetcs of nonhomogeneous processes, Wiley 1987 Reaction AB + X AB + + e - + X AB + X AB * + X AB + X A + B + X AB * AB + + e - Direct Ionization Excitation Dissociation Autoionization

15 Physico-chemical and chemical stage physical stage e sub,h 2 O + A 1 B 1, B 1 A 1 Ryd, db, de s s relax auto-ionize dissociate physiochemical e aq, OH, H, H 2 H 3 O +, OH -, H 2 O 2 diffuse react diffusion coefficients D chemical stage reaction rate constants k H 2 O + + H 2 O H 3 O + + OH A 1 B 1 H 2 O + DE 35% H + OH 65% B 1 A 1 H 2 O + DE 30% H 3 O + + OH + e aq 55% H 2 + OH + OH 15% Ryd,db H 2 O + DE 50% H 3 O + + OH + e aq 50% e aq + e aq + 2H 2 O H 2 + 2OH - e aq + OH OH - e aq + H + H 2 O H 2 + OH - e aq + H 3 O + H + H 2 O e aq + H 2 O 2 OH - + OH OH + OH H 2 O 2 OH + H H 2 O H + H H 2 H 3 O + + OH - 2H 2 O

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17 Radiation induced DNA strand breaks Simple damage electron OH 'Indirect' strand break Base damage SSB 'Direct' strand break H + aq OH H + aq Complex damage Complex SSB DSB Complex DSB Very complex

18 PARTRAC Biophysical Radiation Track Structure Simulation Code photons electrons protons alphas radiation transport track structure module radiation action effect module damage step by step location, deposited energy, kind of interaction water chemistry module production and transport of radiacals geometry module molecules chromatin... cells

19 Track Structure E E spatial information E (x,y,z) Edep type E Follow primary particle produced secondary particles from start/ejection energy down to total stopping step by step total cross sections (IMFP) energy/angle differential cross sections secondary electron spectra E E E E ionization / excitation elastic other

20 Cross Sections and Transport Models: Cross sections: mean free path (elastic + inelastic) single differential double differential triple differential Transport models: angular dependencies secondary electron emission auto ionization / Auger charge changing, multi-ionization, etc

21 Theory: Interaction Cross Sections charged particles atoms DWBA condensed matter energy deposition track structure event-by-event radiation transport DNA damage PWBA molecules cross sections Application: Monte Carlo Simulations

22 Examples Tracks

23 Tracks of low energy electrons

24 Some tracks Electrons, 10 kev

25 Some tracks Alpha particles: MeV

26 Some tracks Carbon ions: MeV/amu

27 Heavy ions (relativistic) 100 MeV/u

28 The Physics What we know What we need to know

29 PARTRAC Transport medium: liquid water electrons: protons: alpha particles: ions: 10 ev 10 MeV 1 kev 1 GeV 1 kev 1 GeV 1 MeV/u 1 GeV/u Considered: Excitations (5 discrete levels) Ionizations (5 ionization shells; single ionizations only) Elastic scattering (electrons only) Charge changing (protons, alphas only; 1,2 electron capture/loss)

30 Geant 4 Geant 4 Geant 4 low electromagnetic Geant 4 - DNA

31 Gas Phase vs. Liquid Phase vs. Condensed Phase low density Gas single atom high density Solid atoms periodic Liquid many atoms disordered Biology: Single cell vs. tissue

32 Light and Heavy Ions at Moderate Speeds Space Radiation / Ion Therapy light ions (C, N, O) in the Bragg peak neutron interactions (secondary cancer; secondary light ions) chemistry: LET/particle type, energy dependence physics: multi-ionization; simultaneous events

33 HZE Interaction Cross Sections Plane wave Born approximation Bethe approximation Scaling laws (velocity and charge) Calculated from proton cross sections bare Consider ions relativistic heavy ion as nonrelativistic point particle

34 Partially dressed ions screening of nuclear charge by other electrons effective charge scaling bare ions: Z eff = Z 0 semiempirical model electron electron interaction nuclear charge Z 0, electrons N far away: Z eff = Z 0 N very close: Z eff = Z 0 Barkas formula: Z eff = Z ( 1 exp( -125 Z -2/3 v/c ))

35 Ions are atomic systems Ionization: target, projectile simple, multiple Excitation: target, projectile simple, multiple Charge changing: electron loss electron capture single, multiple single, multiple

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37 Applications Simulations high LET density of ionizations?? multi-events?? Systems Biology other cell constituents, cell communications, other than radiation

38 Other Materials Than Liquid Water for Track Structure Other Cell Components (for Biology) Other Materials: Gold Nanoparticles Other Materials/Sources: Microsphere Brachytherapy

39 Biological Treatment Planning Introduce micro/nano dosimetric concepts into dose calculations Introduce biology into dose calculations (LEM models)

40 Mixed Radiation Fields Combine nuclear transport with track structure Simulate realistic radiation fields

41 THANK YOU!