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Mesures physiques pour la vérification du parcours des ions en hadronthérapie, Charged particle therapy, ion range verification, prompt radiation

De
144 pages
Sous la direction de Michel Chevallier
Thèse soutenue le 14 octobre 2010: Lyon 1
Cette thèse porte sur les mesures expérimentales des γ-prompts créés lors de la fragmentation du faisceau d'ions carbone en hadronthérapie. Deux expériences ont été effectuées aux laboratoires GANIL et GSI avec des ions 12C6+ de 95MeV/u et 305MeV/u irradiant une cible d'eau ou de PMMA. Dans les deux expériences une nette corrélation a été obtenue entre le parcours des ions carbone et le profil longitudinal des γ- prompts. Une des plus grandes difficultés de ces mesures vient de la discrimination entre le signal des γ-prompts (qui est corrélé avec le parcours des ions) et un important bruit de fond dû aux neutrons (non corrélé au parcours). Deux techniques sont employées pour effectuer la discrimination entre γ et neutrons: le temps de vol (TDV) et la discrimination par forme de signal (DFS). Le TDV a permis de démontrer la corrélation entre la production de γ-prompts et le parcours des ions. La DFS a fourni des informations précieuses pour la compréhension des caractéristiques des spectres en TDV. Dans ce travail on a démontré qu'un système de détection de γ-prompt collimaté, basé sur la technique du temps de vol, peut permettre une vérification en temps réel de la position du Pic de Bragg en conditions cliniques. Dans la dernière partie de la thèse, un travail de simulation a été effectué à l'aide du code de simulation Geant4 pour évaluer l'influence des principaux paramètres du design d'un dispositif de multi-détecteurs et multicollimateurs sur la résolution spatiale et l'efficacité atteignable par une Camera γ-Prompt. Plusieurs configurations géométriques ont été étudiées de façon systématique et les principales contraintes du design sont analysées.
-Hadronthérapie
-Vérification du range en temps réel
-Variation prompte
This PhD thesis reports on the experimental investigation of the prompt photons created during the fragmentation of the carbon beam used in particle therapy. Two series of experiments have been performed at the GANIL and GSI facilities with 95 MeV/u and 305 MeV/u 12C6+ ion beams stopped in PMMA and water phantoms. In both experiments a clear correlation was obtained between the C-ion range and the prompt photon profile. A major issue of these measurements is the discrimination between the prompt photon signal (which is correlated with the ion path) and a vast neutron background uncorrelated with the Bragg-Peak position. Two techniques are employed to allow for this photon-neutron discrimination: the time-of-flight (TOF) and the pulse-shape-discrimination (PSD). The TOF technique allowed demonstrating the correlation of the prompt photon production and the primary ion path while the PSD technique brought great insights to better understand the photon and neutron contribution in TOF spectra. In this work we demonstrated that a collimated set-up detecting prompt photons by means of TOF measurements, could allow real-time control of the longitudinal position of the Bragg-peak under clinical conditions. In the second part of the PhD thesis a simulation study was performed with Geant4 Monte Carlo code to assess the influence of the main design parameters on the efficiency and spatial resolution achievable with a multidetector and multi-collimated Prompt Gamma Camera. Several geometrical configurations for both collimators and stack of detectors have been systematically studied and the considerations on the main design constraints are reported.
-Hadrontherapy
-Charge particle therapy
-Ion range verification
-Prompte radiation
Source: http://www.theses.fr/2010LYO10189/document
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THESE DE L‘UNIVERSITE DE LYON

Délivrée par

L’UNIVERSITE CLAUDE BERNARD LYON 1



ECOLE DOCTORALE PHAST


DIPLOME DE DOCTORAT



Présentée à Lyon le 14 octobre 2010


par


Mauro TESTA


Physical measurements for ion range verification in charged particle therapy



Directeur de thèse : M. Chevallier

Jury : M. M. Chevallier Directeur de thèse
M. R. Ferrand
M. F. Haas Rapporteur
M. C. Lacasta
M. J-M. Moreau Président du jury
Mme K. Parodi
M. C. Ray
M. D. Schardt Rapporteur






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Contents

1 Overview .................................................................................................... 3
1.1 Particle radiation therapy.................................................................................. 3
1.2 Prompt -camera for dose verification and ion range monitoring in particle
therapy. ......................................................................................................................... 4
1.3 Outline of the thesis.......................................................................................... 6
2 Radiation therapy: introduction............................................................... 7
2.1 Physical rationale for particle radiation therapy............................................... 8
2.2 Radiobiological rationale for particle radiation therapy................................. 10
2.3 Particle vs conventional radiation therapy: clinical results and cost analysis 12
2.3.1 Clinical results ........................................................................................ 13
2.3.2 Cost analysis........................................................................................... 15
2.4 Current and future ion therapy centers ........................................................... 16
3 Radiation therapy with ion beams ......................................................... 18
3.1 The physics of interaction of ions with matter ............................................... 18
3.1.1 Inverse depth dose profile: stopping of ions in matter ........................... 18
3.1.2 Range scattering ..................................................................................... 20
3.1.3 Lateral scattering .................................................................................... 22
3.1.4 Ion fragmentation: models and fragments.............................................. 23
3.2 The physics of interaction of photons with matter ......................................... 26
3.2.1 Photoelectric effect, Compton scattering, Pair production..................... 26
3.3 The physics of interaction of neutrons with matter ........................................ 30
4 Current and proposed methods for dose verification and monitoring
in particle therapy .......................................................................................... 32
4.1 PET and TOF-PET ......................................................................................... 32
4.1.1 Ion range verification with PET ............................................................. 36
4.2 Prompt photon radiation ................................................................................. 37
4.2.1 Collimated Prompt Gamma Camera....................................................... 41
4.2.1 Compton Camera.................................................................................... 43
4.3 Interaction Vertex Imaging (IVI) ................................................................... 45
5 Physical measurements of the prompt radiation originated from ion
fragmentation ................................................................................................. 48
5.1 Properties of scintillation detectors ................................................................ 48
5.1.1 Characteristics of BaF – NaI(Tl) – LYSO – BC501 scintillators ......... 50 2
and BC501 scintillators..... 54 5.1.2 Pulse shape discrimination (PSD) for BaF2
2415.1.2.1 PSD test measurements with a Am-Be source ................................... 54
5.1.2.2 PSD test measurements with 14 MeV neutrons ..................................... 58
5.2 Measurements of prompt -rays produced from C-ion fragmentation........... 61
5.2.1 GANIL and GSI single-detector experimental set-up ............................ 61
5.2.1.1 Calculation of detection solid angle and field pf view ........................... 64
5.2.2 GANIL multi-detector experimental set-up ........................................... 66
5.3 Results and discussion.................................................................................... 68
5.3.1 GANIL and GSI single-detector experimental results ........................... 68
5.3.1.1 Time of flight (TOF) spectra analysis .................................................... 68
5.3.1.2 Time of flight (TOF) spectra conditioned by PSD................................. 73
5.3.1.3 Photon and neutron scan profiles............................................................ 77
5.3.1.4 TOF-spectra and prompt photon scan profiles comparisons between
measurements and Geant4 Monte Carlo simulations ............................................. 82
5.3.2 GANIL multi-detector preliminary experimental results ....................... 84
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5.3.2.1 Time of flight (TOF) spectra analysis .................................................... 84
5.3.2.2 Multi detector prompt photon scan profiles ........................................... 86
5.4 Conclusions and perspectives......................................................................... 88
6 Geant4 Monte Carlo simulations for the design of a multi-detector
multi-collimator Prompt Gamma Camera..................................................... 92
6.1 Application of Monte Carlo simulation codes in medical physics................. 92
6.1.1 A short overview of the code architecture and physical models used in
Geant4……………………………………………………………………………..93
6.2 Simulations of a simplified multi-collimated and multi-detector Prompt
Gamma Camera .......................................................................................................... 94
6.2.1 Basic principles of collimator design ..................................................... 94
6.2.2 Description of the simulation set-up....................................................... 95
6.2.3 Basic description of collimator imaging properties................................ 99
6.3 Simulations results and discussion ............................................................... 101
6.3.1 Influence of the collimator design on the detection efficiency ............ 101
6.3.1.1 Influence of the collimator thickness and position on the visibility of the
collimator slit-pattern ........................................................................................... 101
6.3.1.2 Influence of the collimator thickness and position on the detection
efficiency ............................................................................................................. 104
6.3.1.3 Influence of the collimator tiles and slit dimension on the detection
efficiency ............................................................................................................. 108
6.3.2 Influence of the collimator design on the spatial resolution................. 109
6.3.2.1 Influence of the collimator position on the spatial resolution .............. 111
6.3.2.2 Influence of the crystal detector width on the spatial resolution.......... 115
6.3.2.3 Influence of the detection statistics on the spatial resolution ............... 116
6.3.3 Conclusions and perspectives............................................................... 117
7 Summary and outlook........................................................................... 121
8 Appendix................................................................................................ 124
8.1 NaI(Tl) calibration for beam intensity monitoring....................................... 124
8.2 Electronics and acquisition set-up ................................................................ 125
8.2.1 GANIL single-detector experiment...................................................... 125
8.2.2 GSI single-detector experiment............................................................ 127
8.2.3 GANIL multi-detector experiment ....................................................... 127
Bibliography ................................................................................................. 129

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1 Overview
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1.3 Outline of the thesis
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