G. Bartesaghi, 11° ICATPP, Como, 5-9 October 2009 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

G. Bartesaghi, 11° ICATPP, Como, 5-9 October 2009 Outline Boron Neutron Capture Therapy (BNCT): Boron Neutron Capture Therapy (BNCT): a brief introduction Dosimetry and treatment planning in BNCT Dosimetry and treatment planning in BNCT NRI-Rez BNCT facility NRI-Rez BNCT facility Materials & Method: Materials & Method: MC simulations: source and phantoms descriptionMC simulations: source and phantoms description Fricke gel dosimeters Fricke gel dosimeters Results and conclusions Results and conclusions

G. Bartesaghi, 11° ICATPP, Como, 5-9 October B 1n1n 11 B * 7 Li 4 He Gamma (477 keV) 10 B (n,  ) 7 Li (  = 3837 b) Neutrons from nuclear reactors Boron selectively accumulated in tumor cells Boron Neutron Capture Therapy Emission of low range, high LET ions: 4 He 2+ (1.47 MeV) 7 Li 3+ (0.84 MeV) 7 Li 3+ (0.84 MeV) with a range in tissue about one cell diameter.

G. Bartesaghi, 11° ICATPP, Como, 5-9 October 2009 Dosimetry in BNCT What has to be measured? D tot II II D B D B + D p D p + D n D n + D  D  “therapeutic dose”, from 10 B(n,  ) 7 Li  = 3837 b from 14 N(n,p) 14 C E p = 630 keV  = 1.9 b due to epithermal and fast neutron scattering mainly on H nuclei from 1 H(n,γ) 2 H E γ = 2.2 MeV  = 0.33 b and reactor background High complexity: four components, each with different LET and different RBE !!!

G. Bartesaghi, 11° ICATPP, Como, 5-9 October 2009 Three distinct modules are necessary: - dosimetry with an appropriate phantom - Monte Carlo based treatment planning (TP) - 10 B concentration on-line monitoring TP software should be capable to display isodose curves, superimposed to the anatomical images Reactor geometry Patient anatomical images Boron concentration Treatment planning in BNCT

G. Bartesaghi, 11° ICATPP, Como, 5-9 October 2009 BNCT facility at NRI – Rez (Prague) LVR-15 reactor Epithermal column Epithermal neutron flux: 7∙10 8 cm -2 s -1 Nuclear reactor power: 9 MW

G. Bartesaghi, 11° ICATPP, Como, 5-9 October 2009 Thermal neutrons: < 0.4 eV Epithermal neutrons: 0.4 eV < E n < 10 keV Fast neutrons: > 10 keV

G. Bartesaghi, 11° ICATPP, Como, 5-9 October 2009 Treatment room Control room

G. Bartesaghi, 11° ICATPP, Como, 5-9 October 2009 Fixation mask 12 cm diameter collimator

G. Bartesaghi, 11° ICATPP, Como, 5-9 October 2009 Radiation transport and interactions in tissue-equivalent phantoms MC calculations - Neutron transport and thermalization - Boron dose - Neutron dose MCNP5 code Source plane technique (used with MacNCTPLAN): - energy distribution - radial distribution - divergence distribution

G. Bartesaghi, 11° ICATPP, Como, 5-9 October 2009 Tissue equivalent phantoms Standard water phantom 50x50x25 cm 3 Cylindrical water- equivalent phantom d: 16cm, h: 14cm

G. Bartesaghi, 11° ICATPP, Como, 5-9 October 2009 Phantoms reproduced in MCNP5 -Neutron flux on the central plane - Boron dose in 0.5 cm 3 cells - Neutron dose along the beam axis

G. Bartesaghi, 11° ICATPP, Como, 5-9 October 2009 Fricke solution + Xylenol Orange = radiochromic Fricke solution + Xylenol Orange = radiochromic very good tissue equivalence very good tissue equivalence thin layers (up to 3mm thick): thin layers (up to 3mm thick): Fricke Gel dosimeters in form of layers not affecting the in-phantom neutron transport not affecting the in-phantom neutron transport it is possible to modify the gel composition in order to achieve dose components separation it is possible to modify the gel composition in order to achieve dose components separation Standard Gel  -rays and fast neutrons (recoil-protons)  -rays and fast neutrons (recoil-protons) Standard-Gel added with 10 B (40 ppm)  -rays, fast neutrons,  and 7 Li particles  -rays, fast neutrons,  and 7 Li particles Gel like Standard-Gel made with heavy water  -rays and fast neutrons (recoil-deuterons)

G. Bartesaghi, 11° ICATPP, Como, 5-9 October 2009 Boron doseBorated gel Standard gel Boron dose Dose images (15x12 cm 2 ) in the standard water phantom

G. Bartesaghi, 11° ICATPP, Como, 5-9 October 2009 Thermal neutron flux Epithermal neutron flux Fast neutron flux Standard phantom

G. Bartesaghi, 11° ICATPP, Como, 5-9 October 2009 Thermal neutron flux Epithermal neutron flux Fast neutron flux Cylindrical phantom

G. Bartesaghi, 11° ICATPP, Como, 5-9 October 2009 Boron dose distribution Transverse profiles at 3 cm depth

G. Bartesaghi, 11° ICATPP, Como, 5-9 October 2009 Boron dose distribution Transverse profiles at in the cylindrical phantom at different depths

G. Bartesaghi, 11° ICATPP, Como, 5-9 October 2009 Boron dose distribution In-depth on-axis profiles in the two phantoms

G. Bartesaghi, 11° ICATPP, Como, 5-9 October 2009 Fast neutron and gamma doses separation Central profile in the standard water phanton.  (OD) st = α 1 D γ + α 2 D np  (OD) hw = α 3 D γ + α 4 D nd f = D nd /D np = 0.66±0.01 from Monte Carlo

G. Bartesaghi, 11° ICATPP, Como, 5-9 October 2009 Central profile in the standard water phantom. (1) Binns et al., Med Phys, 32 (12), 2005

G. Bartesaghi, 11° ICATPP, Como, 5-9 October 2009 Conclusions Neutron transport, boron dose and neutron dose in tissue-equivalent phantoms have been calculated 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 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 The good agreement confirms the accuracy of the source model used for TP