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N EUTRON SPECTRA IN A TISSUE EQUIVALENT PHANTOM DURING PHOTON RADIOTHERAPY TREATMENT BY LINACS

N EUTRON SPECTRA IN A TISSUE EQUIVALENT PHANTOM DURING PHOTON RADIOTHERAPY TREATMENT BY LINACS. A. Zanini 1 , F. Fasolo 2 , E. Durisi 2 , L. Visca 2 , C. Ongaro 3 , U. Nastasi 4 , K.W. Burn 5 and J.R.M. Annand 6 1 INFN, Via P. Giuria 1, 10125 Torino, Italy

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N EUTRON SPECTRA IN A TISSUE EQUIVALENT PHANTOM DURING PHOTON RADIOTHERAPY TREATMENT BY LINACS

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  1. NEUTRON SPECTRA IN A TISSUE EQUIVALENT PHANTOM DURING PHOTON RADIOTHERAPY TREATMENT BY LINACS A. Zanini1, F. Fasolo2, E. Durisi2, L. Visca2, C. Ongaro3, U. Nastasi4, K.W. Burn5 and J.R.M. Annand6 1 INFN, Via P. Giuria 1, 10125 Torino, Italy 2 Dipartimento Fisica Sperimentale, Università di Torino, Via P. Giuria 1, 10125 Torino, Italy 3Otto, P.zza V. Veneto 14, 10123, Torino, Italy 4Ospedale S. Giovanni Battista A.S., V. Cavour 8, 10133 Torino, Italy 5ENEA ERGPSIEG, V. M. Monte Sole 4, 40129 Bologna, Italy 6Department of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ NEUDOS 9 Ninth Neutron Dosimetry Simposium, Delft September 28 October 3 2003

  2. Outline Photoneutron production in LINACS Monte Carlo Code and Experimental Detection System - Monte Carlo code: MCNP4B-GN - Neutron spectrometer and Unfolding technique - The anthropomorphic phantom TEST of the apparatus (Max Lab, Lund Sweden, JRC Ispra Italy) Results (Onkologik klinik, Lund Sweden) - Neutron spectra at the patient plane - Neutron spectra in phantom - Photoneutron dose in a real treatment Summary NEUDOS 9 Ninth Neutron Dosimetry Simposium, Delft September 28 October 3 2003

  3. Human body P: 12.3 MeV Ca: 15.6 MeV C: 18.7 MeV O: 15.7 MeV Photoneutron production WHERE? Threshold energy (g,n): Accelerator head Neutron leakage Accelerator head W: 7.42 MeV Al: 8 MeV Cu: 9 MeV Fe: 10.9 MeV Gamma beam Photoneutron inside human body NEUDOS 9 Ninth Neutron Dosimetry Simposium, Delft September 28 October 3 2003

  4. MC code and Experimental Detection System Experimental measurements: Phantom • Simulation code: • MCNP-GN • New routine GAMMAN in MCNP4B MCNP-GN: photoneutron generation and transport Bubble detectors: BD-100R BDS spectrometer and unfolding technique: BUNTO Anthropomorphic phantom: JIMMY • Tissue equivalent • Cavities in critical organs positions (ICRP 60) • Conservative with respect to standard phantom (ICRU sphere and water phantom) • Evaluation of neutron spectra at the patient plane. • Evaluation of neutron spectra in tissue equivalent phantom. • The new code MCNP-GN especially aimed at modelling complex geometry with suitable variance reduction techniques NEUDOS 9 Ninth Neutron Dosimetry Simposium, Delft September 28 October 3 2003

  5. Monte Carlo code: MCNP-GN Developed to treat (g,n) neutron production in high and low Z elements and transport in matter, for energies below 30 MeV. MCNP4B-GN capabilities: ·Cross section "Atlas of photoneutron cross section", Bernan. ·Both (g,n) and (g,2n) reactions have been considered. ·Evaporative model: isotropic angular distribution used for low energies. ·Direct model: used for high energies (En > 3 MeV), angular distribution: f (q) = a + b sin2q • Photoneutron production: • The code allows to calculate:  • coordinates of the point of generation • energetic spectrum •  angular distribution Photoneutron transport: Follows the MNCP transport routines NEUDOS 9 Ninth Neutron Dosimetry Simposium, Delft September 28 October 3 2003

  6. Neutron spectrometerBTI (Bubble Tech. Ind., Ontario, Canada) Six different types of superheated drop detector, with different chemical compositions, different thresholds and energetic responses 10 keV - 20 MeV 100 keV - 20 MeV 600 keV - 20 MeV 1 MeV - 20 MeV 2.5 MeV - 20 MeV 10 MeV - 20 MeV 1. BDS 10 2. BDS 100 3. BDS 600 4. BDS 1000 5. BDS 2500 6. BDS 10000 NEUDOS 9 Ninth Neutron Dosimetry Simposium, Delft September 28 October 3 2003

  7. Phantom: Jimmy The anthropomorphic phantom Jimmy has been designed and realized by INFN Sez. Torino, in collaboration with JRC Varese. It consists of a phantom in polyethylene and plexiglas (tissue equivalent material), with inserted human bone in correspondence of column; composition follows the ICRPindications [1]. Cavities are placed in correspondence of critical organs and are suitable to allocate passive dosemeters such as bubble detectors, TLDs, makrofolds. This system allows to evaluate the neutron dose in depth [1] ICRP -Recommendation of the International Commission on Radiological Protection, Pub. n.60, Oxford Pergamon (1991) NEUDOS 9 Ninth Neutron Dosimetry Simposium, Delft September 28 October 3 2003

  8. MCNP-GN TEST - Max Lab, Lund Sweden MCNP-GN tested against a dedicated measurement of W(g,n) production yields at MAX Lab (Lund Sweden): Monochromatic tagged photons (Emax 75 MeV) hitting 4-8mm thick sheet of W. Neutrons are detected in a time of flight spectrometer Annand, Zanini et al. “Photoneutron Yields from Tungsten in the Energy range of the Giant Dipole Resonance”, accepted for publication in “Physics in Medecine and Biology”. NEUDOS 9 Ninth Neutron Dosimetry Simposium, Delft September 28 October 3 2003

  9. BDS TEST – Max Lab, Lund Sweden Measurement of (g,n) yield, made at MAX Lab (Lund Sweden) Bremsstrahlungphoton beam (Emax75 MeV) hits 4mm thick sheet of W and 8mm thick sheet of Pb. Neutrons are detected with BDS spectrometer BDS neutrons target 100 cm Gamma beam NEUDOS 9 Ninth Neutron Dosimetry Simposium, Delft September 28 October 3 2003

  10. PHANTOM TEST Preliminary exposure of the phantom in front of Am/Be source Ispra, Va (JRC): - measure of neutron integral dose (BD-100R) and spectra (BDS) in depth - comparison with simulation results (MCNP-4B code). NEUDOS 9 Ninth Neutron Dosimetry Simposium, Delft September 28 October 3 2003

  11. Elekta Slit with MLC Measurements at Lund Hospital Onkologik Klinik LINAC: Technical details: Photon beam: Emax: 18MeV Target: Tungsten Primary collimator: Tungsten Flattening filter: Stainless Steel Multileaf Collimator (x): Tungsten Jaws (x): Tungsten Jaws (y): Tungsten leaf NEUDOS 9 Ninth Neutron Dosimetry Simposium, Delft September 28 October 3 2003

  12. Neutron spectra at patient plane Patient plane Comparison between measurements and simulation results SSD =100 cm Dose rate: 100UM/Gy x Photon field 10x10 cm2 y ISOCENTRE -15cm -8cm -3cm 3cm 8cm 15cm The data are normalized to 1 Gy photon dose that is the energy released at build up in a water phantom. The build up is at 3cm depth for a 18 MeV end point beam NEUDOS 9 Ninth Neutron Dosimetry Simposium, Delft September 28 October 3 2003

  13. Neutron ambient dose equivalent Comparison between measurements and simulation results Patient plane SSD =100 cm x (energy range: 10keV-20MeV) Photon field 10x10 cm2 y ISOCENTRE -15cm -8cm -3cm 3cm 8cm 15cm • Strong dependence on energy • Information about neutron spectra allows a good knowledge about neutron dose (ICRP 74- Conversion Coefficients for use in Radiological Protection against External Radiation (1995)) NEUDOS 9 Ninth Neutron Dosimetry Simposium, Delft September 28 October 3 2003

  14. Neutron spectra in depth Comparison between measurements and simulation results y x z Photon field at the patient plane 10x10 cm2 The data are normalized to 1 Gy photon dose that is the energy released at build up in a water phantom. NEUDOS 9 Ninth Neutron Dosimetry Simposium, Delft September 28 October 3 2003

  15. Experimental neutron dose in depth • Photon field =10x10 cm2 • dose rate = 100 UM/Gy • SSD = 100 cm • Energy range: 100 keV – 20 MeV • The organs are arranged layer by layer • The organs in each layer are arranged in increasing distance from isocentre Integral measurements: BD-100R NEUDOS 9 Ninth Neutron Dosimetry Simposium, Delft September 28 October 3 2003

  16. Crossed beams treatment to bladder Three photon fields: 0° AP irradiation 90° lateral irradiation 270°lateral irradiation treatment planning to bladder in a patient Lead alloy wedges are used in lateral photon fields for a better dose distribution NEUDOS 9 Ninth Neutron Dosimetry Simposium, Delft September 28 October 3 2003

  17. Crossed beams treatment to bladder Dose rate: 100 UM/Gy treatment planning to bladder in a phantom Neutron Energy range detected: 100 keV – 20 MeV detector: BD100R 3 photon field 10x10cm2 dose delivered in the tumor area 0.1 Gy NEUDOS 9 Ninth Neutron Dosimetry Simposium, Delft September 28 October 3 2003

  18. Crossed beams treatment to bladder Undesired neutron dose in a real treatment compared with the neutron dose measured during an exposure to ONE photon beam Neutron Energy range detected : 100 keV – 20 MeV one g beam R T Organ H*(10) mSv/Gy liver 0.450.41 esophagus 0.38 0.45 right colon 0.38 0.45 left colon 0.45 0.37 stomach 0.12 0.18 right lung 0.13 0.26 left lung 0.15 0.15 thyroid 0.19 0.20 brain 0.13 0.30 spleen 0.07 0.48 left kidney 0.031 0.21 low column 0.024 0.20 right kidney 0.06 0.25 middle column 0.024 0.20 Real treatment Higher neutron doses in deeper organs NEUDOS 9 Ninth Neutron Dosimetry Simposium, Delft September 28 October 3 2003

  19. Summary • For the first time, a complete apparatus for the evaluation of neutron spectra inside an anthropomorphic tissue - equivalent phantom has been developed. • The new routine GAMMAN implemented in MCNP4B code simulates the photoneutron production in accelerator head and in the phantom and retains the ability of MCNP to transport neutrons, photons and electrons through complex geometries. • This method may be applied in view of the optimization of the radiotherapy treatment (Council Directive 97 EURATOM on health protection of individuals against the dangers of ionizing radiation in relation to medical exposure.) Acknowledgments • We acknowledge: • the support of the Max Lab, Lund – Sweden; • the research group and the UK Engineering and Physical Science Research Council; • the ENEA (Italian National Agency for New Technologies, Energy and the Environment). NEUDOS 9 Ninth Neutron Dosimetry Simposium, Delft September 28 October 3 2003

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