Distribuzione di radicali liberi in dosimetri EPR irradiati con radiazioni di diverso LET

Transcript

1 Distribuzione di radicali liberi in dosimetri EPR irradiati con radiazioni di diverso LET M. Marralea,b, A. Longoa,b, M. Braia,b, A. Barbonc, M. Brustolonc, G.A.P. Cirroned, F. Romanod,e, F. Di Rosaf, G.Cuttoned Dipartimento di Fisica, Università di Palermo b Sezione INFN di Catania Catania c Dipartimento di Scienze Chimiche, Università di Padova e INFN Sezione di Padova d Laboratori Nazionali del Sud-INFN Catania e Museo Storico della Fisica e Centro Studi e Ricerche "E. Fermi" Roma f Azienda Sanitaria Provinciale N 2, Pres. Osped. "M. Raimondi" S. Cataldo (CL) a maurizio.marrale@unipa.it

2 Hadrontherapy vs photon radiotherapy

3 Hadrontherapy vs photon radiotherapy

4 Hadrontherapy vs photon radiotherapy

5 Differences in Relative Biological Effectiveness Cell response depends on Linear Energy Transfer (LET) The surviving cell fraction decreases with LET Hall E. J. (2000). Radiation Biology for the Radiologist. Lippincott Williams & Wilkins: Philadelphia.

6 Differences in Relative Biological Effectiveness Cell response depends on Linear Energy Transfer (LET) The surviving cell fraction decreases with LET Hall E. J. (2000). Radiation Biology for the Radiologist. Lippincott Williams & Wilkins: Philadelphia. Cucinotta, F. A. & Durante, M. Lancet Oncol. (2006)

7 Radiation interaction in nanometer dimensions In order to optimize the therapy it is necessary to grasp the mechanisms on the basis of the biological damages induced by ionizing radiations.

8 Radiation interaction in nanometer dimensions In order to optimize the therapy it is necessary to grasp the mechanisms on the basis of the biological damages induced by ionizing radiations. Analysis of the Track Structure Figures from Hans Rabus, PTB (Germany)

9 Target of this work

10 Target of this work This work is aimed at the analysis of the distribution of free radicals produced by various LET radiations through Electron Spin Resonance (ESR or EPR) technique. This spectroscopic tool allows dose measurements via the detection of the free radicals produced by ionizing radiations.

11 Target of this work This work is aimed at the analysis of the distribution of free radicals produced by various LET radiations through Electron Spin Resonance (ESR or EPR) technique. This spectroscopic tool allows dose measurements via the detection of the free radicals produced by ionizing radiations. In this work we analyzed and simulated the experimental results obtained by Pulse ESR techniques with the aim of obtaining information about the microscopic local concentration and the spin-spin distance distribution of free radicals.

12 ORGANIC COMPOUND USED AMMONIUM TARTRATE (AT) STRUCTURE ESR spectrum. M. Brustolon, A. L. Maniero, S. Jovine, and U. Segre, Res. Chem. Intermed. 22(4), 359 (1996). Powder samples

13 Free radicals distributions for radiations with various LET

14 Free radicals distributions for radiations with various LET Low LET radiations Small local concentration of free radicals

15 Free radicals distributions for radiations with various LET Low LET radiations High LET radiations Small local concentration of free radicals High local concentration of free radicals

16 LET in Ammonium tartrate 60Co γ-photons 19.3 MeV protons 0.62 MeV protons (thermal neutrons) AVERAGE EFFECTIVE LET ~ 0.35 kev/µm ~ 4.5 kev/µm ~ 70 kev/µm We have used for protons simulations the TRIM software for photon simulations the MCNP software.

17 Pulsed EPR techniques employed Two pulses EPR echo decay with varying microwave power intensity in order to obtain information about the microscopic local concentration of free radicals for pellets exposed to various radiation beams. Double Electron-Electron Resonance (DEER) in order to obtain information about the spin-spin distance distributions for pellets exposed to various radiation beams.

18 Two pulses EPR echo decay analysis

19 Two pulses EPR echo decay analysis AT exposed to 5kGy of gamma photons. Tm SIF Napoli Settembre 2012 XCVIII Congresso Nazionale

20 Two pulses EPR echo decay analysis

21 Local microscopic concentration of free radicals AVERAGE EFFECTIVE LET ~ 0.35 kev/µm ~ 4.5 kev/µm ~ 70 kev/µm High LET radiations (protons and thermal neutrons) are characterized by larger ratio Cmicroscopic/Cmacroscopic values than low LET radiations. M. Marrale, M. Brai, A. Barbon, M. Brustolon Radiat. Res. (2009) 171,

22 Two pulses EPR echo decay analysis Conclusions This technique is able to distinguish low LET radiations (such as 60Co γ-photons) from high LET radiations (19.3 MeV protons and thermal neutrons). The similarity of the microscopic concentrations of protons and thermal neutrons could be ascribed to radicals recombination.

23 Double Electron-Electron resonance (DEER) Measures dipolar coupling between spatially separated unpaired electrons using pulsed EPR Dipolar coupling is related to radical separation Hamiltonian: µ ( S.r )( S.r ) S.S Hˆ dd = 0 g1 g 2 µ β π r r

24 Double electron-electron resonance (DEER) Pump Observe Δν π/2 Δν Frequency / MHz 2 π π τ π Distance / nm 0 2 / μsettembre s XCVIII Congresso Nazionale SIF NapoliTime Janet Banham Testing the Limits of the DEER Method for Distance Measurements in Proteins Oxford University

25 Double electron-electron resonance (DEER) Pump Observe Δν π/2 Δν Frequency / MHz 2 π π τ π Distance / nm 0 2 Time / μs Janet Banham Testing the Limits of the DEER Method for Distance Measurements in Proteins Oxford University

26 Double electron-electron resonance (DEER) Pump Observe Δν π/2 Δν Frequency / MHz 2 π π τ π Distance / nm 0 2 Time / μs Janet Banham Testing the Limits of the DEER Method for Distance Measurements in Proteins Oxford University

27 Double Electron Electron Resonance (DEER) ν pump ν detection

28 Distance distributions of free radicals M. Marrale, M. Brai, A. Barbon, M. Brustolon Radiat. Res. (2009) 171,

29 Distance distributions of free radicals These curves are affected by two factors: the lattice structure of the ammonium tartrate microcrystals in powders; the spatial distribution of free radicals produced by ionizing radiations inside the volume M. Marrale, M. Brai, A. Barbon, M. Brustolon Radiat. Res. (2009) 171,

30 Free radicals distributions assumed for simulations

31 Free radicals distributions assumed for simulations 19.3 MeV Protons

32 Free radicals distributions assumed for simulations 19.3 MeV Protons Co γ -photons 60

33 Distance distributions of free radicals Good agreement between experimental data and simulation results. M. Marrale, M. Brai, A. Barbon, M. Brustolon Radiat. Res. (2009) 171,

34 Double Electron Electron Resonance (DEER) Conclusions This pulse EPR technique discriminates samples exposed to γ-photons from those exposed to protons. The radical distributions assumed for protons (cylindrical distribution) and photons (spherical distribution) exposure give rise to a good agreement between experimental data and simulations. Analyses on crystal samples exposed to various radiation beams (such as photons, thermal neutrons and ions) are in progress.

35 Acknowledgements We acknowledge funding from the Project NORMET of the Istituto Nazionale di Fisica Nucleare (INFN) Gruppo V. National Project Leader: Dr. Maurizio Marrale The research here described is related to the Project Biologically weighted quantities in radiotherapy (BIOQUART) EMRP European Metrology Research Programme. Project Leader: Dr. Hans Rabus (PTB, Braunschweig, Germany)

36 Thank you for your attention!