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G. Bartesaghi, G. Gambarini, A. Negri

MONTE CARLO SIMULATIONS ON NEUTRON TRANSPORT AND ABSORBED DOSE IN TISSUE-EQUIVALENT PHANTOMS EXPOSED TO HIGH-FLUX EPITHERMAL NEUTRON BEAMS. G. Bartesaghi, G. Gambarini, A. Negri. Department of Physics of the University of Milan and INFN, Milan, Italy. J. Burian, L. Viererbl.

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G. Bartesaghi, G. Gambarini, A. Negri

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  1. MONTE CARLO SIMULATIONS ON NEUTRON TRANSPORT AND ABSORBED DOSE IN TISSUE-EQUIVALENT PHANTOMS EXPOSED TO HIGH-FLUX EPITHERMAL NEUTRON BEAMS G. Bartesaghi, G. Gambarini, A. Negri Department of Physics of the University of Milan and INFN, Milan, Italy J. Burian, L. Viererbl Department of Reactor Physics, Nuclear Research Institute Rez, Czech Republic

  2. Outline • Boron Neutron Capture Therapy (BNCT): • a brief introduction • Dosimetry and treatment planning in BNCT • NRI-Rez BNCT facility • Materials & Method: • MC simulations: source and phantoms description • Fricke gel dosimeters • Results and conclusions

  3. 7Li 11B* 4He 1n 10B Boron Neutron Capture Therapy Boron selectively accumulated in tumor cells Neutronsfrom nuclear reactors 10B (n,)7Li( = 3837 b) Gamma (477 keV) Emission of low range, high LET ions: 4He2+ (1.47 MeV) 7Li3+ (0.84 MeV) with a range in tissue about one cell diameter.

  4. Dosimetry in BNCT What has to be measured? Dtot II DB + Dp + Dn + D “therapeutic dose”, from 10B(n,)7Li  = 3837 b from 14N(n,p)14C Ep= 630 keV = 1.9 b due to epithermal and fast neutron scattering mainly on H nuclei from 1H(n,γ)2H Eγ = 2.2 MeV  = 0.33 b and reactor background High complexity: four components, each with different LET and different RBE !!!

  5. Three distinct modules are necessary: • dosimetry with an appropriate phantom • Monte Carlo based treatment planning (TP) • 10B concentration on-line monitoring Treatment planning in BNCT Reactor geometry Patient anatomical images Boron concentration TP software should be capable to display isodose curves, superimposed to the anatomical images

  6. LVR-15 reactor Epithermal column BNCT facility at NRI – Rez (Prague) Nuclear reactor power: 9 MW Epithermal neutron flux: 7∙108 cm-2 s-1

  7. Thermal neutrons: < 0.4 eV Epithermal neutrons: 0.4 eV < En < 10 keV Fast neutrons: > 10 keV

  8. Treatment room Control room

  9. Fixation mask 12 cm diameter collimator

  10. MC calculations Radiation transport and interactions in tissue-equivalent phantoms • Neutron transport and thermalization • Boron dose • Neutron dose MCNP5 code Source plane technique (used with MacNCTPLAN): • energy distribution • radial distribution • divergence distribution

  11. Tissue equivalent phantoms Standard water phantom 50x50x25 cm3 Cylindrical water-equivalent phantom d: 16cm, h: 14cm

  12. Phantoms reproduced in MCNP5 • Neutron flux on the central plane • Boron dose in 0.5 cm3 cells • - Neutron dose along the beam axis

  13. Fricke Gel dosimeters in form of layers • Fricke solution + Xylenol Orange = radiochromic • very good tissue equivalence • thin layers (up to 3mm thick): • not affecting the in-phantom neutron transport • it is possible to modify the gel composition in order to achieve dose components separation Standard Gel -rays and fast neutrons (recoil-protons) Standard-Gel added with 10B (40 ppm) -rays, fast neutrons,  and 7Li particles Gel like Standard-Gel made with heavy water -rays and fast neutrons (recoil-deuterons)

  14. Standard gel Boron dose Borated gel Boron dose Dose images (15x12 cm2) in the standard water phantom

  15. Thermal neutron flux Standard phantom Fast neutron flux Epithermal neutron flux

  16. Thermal neutron flux Cylindrical phantom Fast neutron flux Epithermal neutron flux

  17. Boron dose distribution Transverse profiles at 3 cm depth

  18. Boron dose distribution Transverse profiles at in the cylindrical phantom at different depths

  19. Boron dose distribution In-depth on-axis profiles in the two phantoms

  20. Fast neutron and gamma doses separation (OD)st= α1Dγ + α2Dnp (OD)hw = α3Dγ + α4Dnd f = Dnd/Dnp = 0.66±0.01 from Monte Carlo Central profile in the standard water phanton.

  21. (1) Binns et al., Med Phys,32 (12), 2005 Central profile in the standard water phantom.

  22. Conclusions • Neutron transport, boron dose and neutron dose in tissue-equivalent phantoms have been calculated • Boron and fast neutron doses have been measured by means of Fricke gel layers • The good agreement confirms the accuracy of the source model used for TP

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