Bragg Peak Localization with Piezoelectric Sensors for Proton Therapy Treatment

[EN] A full chain simulation of the acoustic hadrontherapy monitoring for brain tumours is presented in this work. For the study, a proton beam of 100 MeV is considered. In the first stage, Geant4 is used to simulate the energy deposition and to study the behaviour of the Bragg peak. The energy deposition in the medium produces local heating that can be considered instantaneous with respect to the hydrodynamic time scale producing a sound pressure wave. The resulting thermoacoustic signal has been subsequently obtained by solving the thermoacoustic equation. The acoustic propagation has been simulated by FEM methods in the brain and the skull, where a set of piezoelectric sensors are placed. Last, the final received signals in the sensors have been processed in order to reconstruct the position of the thermal source and, thus, to determine the feasibility and accuracy of acoustic beam monitoring in hadrontherapy.This research received was funded by the Spanish Agencia Estatal de Investigacion, grant numbers FPA2015-65150-C3-2-P (MINECO/FEDER) and PGC2018-096663-B-C43 (MCIU/FEDER).Otero-Vega, JE.; Felis-Enguix, I.; Herrero Debón, A.; Merchán, JA.; Ardid Ramírez, M. (2020). Bragg Peak Localization with Piezoelectric Sensors for Proton Therapy Treatment. Sensors. 20(10):1-12. https://doi.org/10.3390/s20102987S1122010A population-based assessment of proton beam therapy utilization in California. (2020). The American Journal of Managed Care, 26(2), e28-e35. doi:10.37765/ajmc.2020.42398Dutz, A., Agolli, L., Bütof, R., Valentini, C., Baumann, M., Lühr, A., … Krause, M. (2020). Neurocognitive function and quality of life after proton beam therapy for brain tumour patients. Radiotherapy and Oncology, 143, 108-116. doi:10.1016/j.radonc.2019.12.024Lesueur, P., Calugaru, V., Nauraye, C., Stefan, D., Cao, K., Emery, E., … Thariat, J. (2019). Proton therapy for treatment of intracranial benign tumors in adults: A systematic review. Cancer Treatment Reviews, 72, 56-64. doi:10.1016/j.ctrv.2018.11.004Amaldi, U., Bonomi, R., Braccini, S., Crescenti, M., Degiovanni, A., Garlasché, M., … Zennaro, R. (2010). Accelerators for hadrontherapy: From Lawrence cyclotrons to linacs. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 620(2-3), 563-577. doi:10.1016/j.nima.2010.03.130Weber, D. C., Abrunhosa-Branquinho, A., Bolsi, A., Kacperek, A., Dendale, R., Geismar, D., … Grau, C. (2017). Profile of European proton and carbon ion therapy centers assessed by the EORTC facility questionnaire. Radiotherapy and Oncology, 124(2), 185-189. doi:10.1016/j.radonc.2017.07.012MIZUMOTO, M., OSHIRO, Y., YAMAMOTO, T., KOHZUKI, H., & SAKURAI, H. (2017). Proton Beam Therapy for Pediatric Brain Tumor. Neurologia medico-chirurgica, 57(7), 343-355. doi:10.2176/nmc.ra.2017-0003Sulak, L., Armstrong, T., Baranger, H., Bregman, M., Levi, M., Mael, D., … Learned, J. (1979). Experimental studies of the acoustic signature of proton beams traversing fluid media. Nuclear Instruments and Methods, 161(2), 203-217. doi:10.1016/0029-554x(79)90386-0Aso, T., Kimura, A., Tanaka, S., Yoshida, H., Kanematsu, N., Sasaki, T., & Akagi, T. (2005). Verification of the dose distributions with GEANT4 simulation for proton therapy. IEEE Transactions on Nuclear Science, 52(4), 896-901. doi:10.1109/tns.2005.852697Jones, K. C., Witztum, A., Sehgal, C. M., & Avery, S. (2014). Proton beam characterization by proton-induced acoustic emission: simulation studies. Physics in Medicine and Biology, 59(21), 6549-6563. doi:10.1088/0031-9155/59/21/6549Jones, K. C., Seghal, C. M., & Avery, S. (2016). How proton pulse characteristics influence protoacoustic determination of proton-beam range: simulation studies. Physics in Medicine and Biology, 61(6), 2213-2242. doi:10.1088/0031-9155/61/6/2213Donnelly, B. R., & Medige, J. (1997). Shear Properties of Human Brain Tissue. Journal of Biomechanical Engineering, 119(4), 423-432. doi:10.1115/1.2798289Gu, L., Chafi, M. S., Ganpule, S., & Chandra, N. (2012). The influence of heterogeneous meninges on the brain mechanics under primary blast loading. Composites Part B: Engineering, 43(8), 3160-3166. doi:10.1016/j.compositesb.2012.04.014Peterson, J., & Dechow, P. C. (2003). Material properties of the human cranial vault and zygoma. The Anatomical Record, 274A(1), 785-797. doi:10.1002/ar.a.10096Fellah, Z. E. A., Chapelon, J. Y., Berger, S., Lauriks, W., & Depollier, C. (2004). Ultrasonic wave propagation in human cancellous bone: Application of Biot theory. The Journal of the Acoustical Society of America, 116(1), 61-73. doi:10.1121/1.1755239Raffaele, L. (2016). Advances in hadrontherapy dosimetry. Physica Medica, 32, 187. doi:10.1016/j.ejmp.2016.07.323Dosanjh, M., Amaldi, U., Mayer, R., & Poetter, R. (2018). ENLIGHT: European network for Light ion hadron therapy. Radiotherapy and Oncology, 128(1), 76-82. doi:10.1016/j.radonc.2018.03.014Ahmad, M., Xiang, L., Yousefi, S., & Xing, L. (2015). Theoretical detection threshold of the proton-acoustic range verification technique. Medical Physics, 42(10), 5735-5744. doi:10.1118/1.4929939Smith, A., Gillin, M., Bues, M., Zhu, X. R., Suzuki, K., Mohan, R., … Matsuda, K. (2009). The M. D. Anderson proton therapy system. Medical Physics, 36(9Part1), 4068-4083. doi:10.1118/1.3187229Yock, T. I., & Tarbell, N. J. (2004). Technology Insight: proton beam radiotherapy for treatment in pediatric brain tumors. Nature Clinical Practice Oncology, 1(2), 97-103. doi:10.1038/ncponc0090Riva, M., Vallicelli, E. A., Baschirotto, A., & De Matteis, M. (2018). Acoustic Analog Front End for Proton Range Detection in Hadron Therapy. IEEE Transactions on Biomedical Circuits and Systems, 12(4), 954-962. doi:10.1109/tbcas.2018.2828703Acoustics Module User’s Guidehttps://doc.comsol.com/5.4/doc/com.comsol.help.aco/AcousticsModuleUsersGuide.pdfArdid, M., Felis, I., Martínez-Mora, J. A., & Otero, J. (2017). Optimization of Dimensions of Cylindrical Piezoceramics as Radio-Clean Low Frequency Acoustic Sensors. Journal of Sensors, 2017, 1-8. doi:10.1155/2017/8179672Otero, Felis, Ardid, & Herrero. (2019). Acoustic Localization of Bragg Peak Proton Beams for Hadrontherapy Monitoring. Sensors, 19(9), 1971. doi:10.3390/s19091971Levenberg, K. (1944). A method for the solution of certain non-linear problems in least squares. Quarterly of Applied Mathematics, 2(2), 164-168. doi:10.1090/qam/10666Geant4 A Simulation Toolkithttp://geant4-userdoc.web.cern.ch/geant4-userdoc/UsersGuides/ForApplicationDeveloper/BackupVersions/V10.5-2.0/fo/BookForApplicationDevelopers.pdfBarber, T. W., Brockway, J. A., & Higgins, L. S. (1970). THE DENSITY OF TISSUES IN AND ABOUT THE HEAD. Acta Neurologica Scandinavica, 46(1), 85-92. doi:10.1111/j.1600-0404.1970.tb05606.xAdrián-Martínez, S., Bou-Cabo, M., Felis, I., Llorens, C. D., Martínez-Mora, J. A., Saldaña, M., & Ardid, M. (2015). Acoustic Signal Detection Through the Cross-Correlation Method in Experiments with Different Signal to Noise Ratio and Reverberation Conditions. Lecture Notes in Computer Science, 66-79. doi:10.1007/978-3-662-46338-3_

Commissioning of a Compton camera for medical imaging

The interest of using hadron-therapy in cancer treatment, particularly for tumors in the vicinity of critical organs-at-risk, is continuously growing due the ability of this treatment modality to provide high precision dose delivery. In order to fully exploit this beneficial property, it is mandatory to ensure that the well-localized dose deposition (Bragg peak) is located in the tumor volume. This calls for a precise in-vivo monitoring of the particle (proton, ion) beam stopping range. Therefore, the purpose of our project is to develop an in-vivo imaging system based on a Compton camera to verify the particle beam range by detecting (multi-MeV) prompt γ rays, generated as a result of nuclear reactions between the particle beam and biological tissue. In the context of this thesis the prototype of the LMU Compton camera was considerably improved and upgraded, and characterized both in the laboratory as well as under online conditions with particle beams at various accelerator facilities. The Compton camera consists of two main components: a scatterer (tracker), formed by a stack of six double-sided Si-strip detectors (DSSSD), and a monolithic LaBr 3 :Ce scintillation detector (5x5x3 cm 3 ), acting as absorber. The highly segmented DSSSD detectors, each with 128 strips per side (strip pitch: 0.39 mm), is processed by a compact ASIC-based electronics (1536 signal channels), while the scintillation detector is read out by a 256-fold segmented, position-sensitive multi-anode photomultiplier tube, providing energy and time information for each PMT segment. The stacked design of the LMU Compton camera scatter detector allows not only to reconstruct the incident photon origin, but it also allows to track Compton scattered electrons, thus enhancing the reconstruction efficiency compared to the conventional design. The Compton camera absorber (LaBr 3 :Ce scintillator crystal) was characterized in two different side-surface wrapping scenarios, absorptive and reflective. (Position-dependent) energy resolution and time resolution were determined for both coating scenarios, revealing the superior properties of the advanced scintillator material in case of the reflectively coated crystal, providing excellent energy (position independent: ∆E/E =3.8 % at 662 keV) and time resolution (273(6) ps FWHM). In addition, the impact of the crystal wrapping options on the scintillation light distribution was studied by extracting the Light Spread Function (LSF) from the crystal irradiation with a collimated 137 Cs source. Here, as can be expected, the absorptively coated crystal reveals a slightly better FWHM value of the LSF compared to the reflectively coated detector. Nevertheless, the drastic improvement of the other properties with reflective coating motivated this choice for the Compton camera absorber. The capability of the monolithic LaBr 3 :Ce scintillator to provide the γ-ray interaction position, which is a mandatory prerequisite for the targeted photon source reconstruction based on Compton scattering, was determined by applying two specific algorithms (’k-nearest neighbor’(k-NN) and ’Categorical Average Pattern’ (CAP)). These algorithms require a large reference data base of 2D scintillation light amplitude distributions, acquired by perpendicularly irradiating the scintillator front surface with a tightly (1 mm diameter) collimated photon source on a fine grid (0.5 mm step size). Two γ-ray sources, 137 Cs and 60 Co, were used to generate the required reference libraries in order to study the energy-dependent spatial resolution of the LaBr 3 :Ce scintillator. Systematic parameter studies were performed as a function of the photon energy, PMT granularity, irradiation grid size and number of photopeak events acquired in each of the 10 4 irradiation positions. Optimum values for the spatial resolution were achieved with 4.8(1) mm (FWHM) at 662 keV and 3.7(1) mm (FWHM) at 1.3 MeV using the CAP algorithm,thus almost reaching the final design goal of 3 mm envisaged for the prompt-γ energy region of 4-6 MeV. With the observed trend of improving spatial resolution with increasing photon energy, it will be interesting to study this property beyond the realm of γ-ray calibration sources in the higher energy region beyond 4 MeV, provided the availablility of an intense, monoenergetic and collimated photon beam. Furthermore, the Compton camera has been commissioned at different particle beam facilities. The camera components were first calibrated and characterized with monoenergetic 4.44 MeV γ rays generated via the nuclear 15 N(p,αγ) 12 C ∗ reaction at the Helmholtz-Zentrum Dresden Rossendorf (HZDR). The response of both the scatter and absorber detectors was found in good agreement with Monte-Carlo simulations. Moreover, the time-of-flight (TOF) measurement capability of the absorbing scintillator was studied at the Garching Tandem accelerator, using a 20 MeV pulsed (400 ns) deuteron beam hitting a water phantom, showing prompt γ rays well separated from the slower neutron background. The camera was finally commissioned with different clinical proton beams (100 MeV, 160 MeV and 225 MeV) at the research area of the Universitäts Protonen Therapie Dresden, stopping either in a water or a PMMA phantom. Energy spectra were acquired and separated into their prompt and delayed components, extracting the prompt photon contribution via TOF. The Compton electron energy deposit in each DSSSD layer was determined and found in very good agreement with simulation expectations. Hit multiplicities and the correlated electron tracking capability of the scatter/tracker array were investigated and limitations imposed by the present ASIC-based readout electronics, as well as options for further improvements, were identified

Monitorización acústica con cerámicas piezoeléctricas en aplicaciones médicas con haces de protones

[ES] En este artículo se presenta la monitorización acústica del uso de partículas pesadas en tratamientos oncológicos con haces de protones a partir del estudio de la señal de presión generada por el efecto termoacústico debido a la incidencia de un haz de protones con una energía de 100 MeV para un caso específico de ependioma. El perfil espacial de la deposición de energía ha sido simulado empleando el método Monte Carlo en la herramienta de cálculo Geant4 junto con las librerías disponibles para incluir la interacción de las partículas con el tejido cerebral y la estructura ósea del cráneo. La señal termoacústica resultante es obtenida discretizando una solución particular de la ecuación de ondas termoacústica. Con esto, la fase de propagación y transmisión se ha simulado empleando el método de elementos finitos (FEM). Finalmente, se ha reconstruido la posición de la fuente de energía depositada evaluando el tiempo de llegada (TOA) a un conjunto de puntos sobre la superficie del cráneo.[EN] This article presents the acoustic monitoring of the use of heavy particles in oncological treatments with proton beams from the study of the pressure signal generated by the thermoacoustic effect due to the incidence of a proton beam with an energy of 100 MeV for a specific case of ependyoma. The spatial profile of the energy deposition has been simulated using the Monte Carlo method in the Geant4 calculation tool together with the available libraries to include the interaction of the particles with the brain tissue and the bone structure of the skull. The resulting thermoacoustic signal is obtained by discretizing a particular solution of the thermoacoustic wave equation. With this, the propagation and transmission phase has been simulated using the finite element method (FEM). Finally, the position of the deposited energy source has been reconstructed by evaluating the time of arrival (TOA) at a set of points on the surface of the skull.Otero-Vega, JE.; Felis-Enguix, I.; Ardid Ramírez, M.; Herrero Debón, A. (2020). Monitorización acústica con cerámicas piezoeléctricas en aplicaciones médicas con haces de protones. Revista de Acústica. 51(3-4):3-9. http://hdl.handle.net/10251/176278S39513-

Increased Proton Energies - Above the ~ 60 MeV Empirical Barrier, from High-Contrast High-Intensity Short-Pulse Laser-Interactions with Micro-Cone Targets

Ultra-high intensity lasers enable the investigation of extreme states of matter and the study of high energy density physics in the laboratory, as well as the creation of various intense radiation sources, i.e. electrons, X-rays, and ions. Of particular interest to this dissertation is the production of ion beams from solid targets. These ion beams are directly linked to the hot-electron production and transport inside the solid target (as simple as a metal or CH foil), which requires that electron heating and transport must be well understood in order to increase ion energies and laser-ion conversion efficiencies. Maximizing the energy and/or the conversion efficiency of these ion beams is of considerable interest for many applications, in particular radiation oncology, and inertial confinement fusion with fast ignition. Several approaches have been proposed to maximize the energy and/or the conversion efficiency of the ion beams: instead of using regular size flat-foil targets (i.e. ~ 10 µm thickness, ~ 2x2 mm^2 lateral dimensions), one can use ultrathin targets (thickness of the order of the µm or 100s of nm), very small targets, a.k.a. reduced-mass targets (RMTs) (i.e. lateral dimensions of ~ 100x100 µm^2), or structured targets (e.g. conical-shape targets). These more elaborate targets can increase the hot-electron temperature and/or the hot-electron density. In experiments performed in 2006 on the Trident laser at ~ 20 J, reported in [1], we found that microstructured flat-top cone (FTC) targets, made from Au, yielded an increase in proton energy from 19 MeV to > 30 MeV, and in laser-proton conversion efficiencies from 0.5 % to 2.5 %, as compared to flat-foil targets. These results were postulated to stem from improved laser guiding toward the cone tip, which would lead to higher laser intensities, increased laser absorption and hotter electrons. Improved electron production and transport were also hypothesized to lead to an increase in the hot-electron density and hot-electron temperature at the flat-top. Also postulated was the fact that a longer electron confinement time at the flat-top could lead to RMT-like effects such as resistive/confining edge fields and enhanced target (or flat-top) charge up. We also observed experimentally that, when the laser was misaligned and could not reach the cone tip, or from simulations that, when it was absorbed farther from the flat-top due to an excess in preplasma, the proton acceleration was neither as efficient nor as energetic.After these very promising 2006 results, we endeavored to determine whether this enhancement in proton energy and conversion efficiency would scale for higher laser energies. I participated in the design and the execution of the subsequent experiment, which was performed in 2008, after the Trident laser energy had been upgraded from ~ 20 J to ~ 80 J. This time, surprisingly, we found that the proton energies were in fact lower when FTC targets were used, as opposed to flat-foil targets [2]. To diagnose the laser absorption zone inside the FTC, Cu targets were used (instead of Au) for the purpose of Cu Ka 2-D imaging. I had taken part in an experiment on the LULI laser system earlier in 2008 to learn about Cu Ka imaging techniques; in this experiment, it was observed that, when a portion of the hot-electron population deposits its energy in the laser absorption zone, the emission of Cu Ka X-rays is a direct indication of where the electrons are created, and thus of how much preplasma is filling the cone neck [3]; preplasma is plasma from wall blow-off due to the low level of laser light entering the cone before the main high-intensity pulse, called laser "prepulse". Combining and correlating Cu Ka 2-D imaging with proton acceleration was one of my main goals for this dissertation. At an intrinsic 10^-8 laser contrast, unlike in the 20 J (and ~ 10^19 W/cm^2) case, at 80 J (and ~ 2x10^20 W/cm^2), after the Trident energy enhancement, as well as the addition of a deformable mirror resulting in a spot size decrease from ~ 14 µm down to ~ 7 µm FWHM (with 47 % of the energy in the spot), the amount of plasma prefill (preplasma) prevented the majority of the laser from being efficiently absorbed closer to the cone flat-top or tip [3,4]. The hot-electron population was thus generated away from the flat-top, as indicated by the Cu Ka emission from the cone walls [2], which negatively impacted the proton acceleration, especially in the case of thin FTC necks [1], as the electrons were also not efficiently transported to the flat-top to generate the sheath necessary for ion production. I was also responsible for the electron spectrometer diagnostic; electron spectroscopy confirmed that the temperature of the escaping electrons correlates in a linear fashion with proton energy. Because of the preplasma issues encountered in 2008 due to an insufficient laser contrast (10^-8), I proposed and was the principal investigator of the most recent experiment (2009), which was performed on Trident at ~ 80 J using an enhanced contrast, i.e. this time > 10^-10. In this case, the proton energies were enhanced to 67.5 MeV [5] from 50 MeV when using FTC Cu targets as opposed to flat-foil targets. These results set a new record in laser-accelerated protons. The previous petawatt laser record was 58 MeV with ~ 400 J [6]. Electron spectroscopy in the enhanced contrast case shows an even better correlation with proton energy, due to a cleaner interaction caused by a lower preplasma level. Besides diagnosing the laser alignment or misalignment, I show in this dissertation via Cu Ka imaging, that not only is it crucial to obtain laser absorption at the tip (note that tip heating is dependent on laser contrast and laser intensity [3]), but it is even more important to find the optimum balance [5] between the amount of cone wall emission (CWE) versus top emission (TE) of Cu Ka X-rays. Interestingly, at enhanced contrast, the best results for proton acceleration are obtained when the target-laser interaction is asymmetric: i.e. when the laser interacts with the cone-tip and one sidewall more so than the opposing side. These experimental results directly led to simulations of these asymmetric interactions using a particle-in-cell (PIC) code capable of simulating ultra-intense laser-matter interactions. These simulations results significantly broadened our understanding of this interaction, and explain why the best performing target has a very large neck (i.e. 160 µm), implying that laser light guiding resulting from the cone geometry is not essential, but rather that the grazing of the laser light on as much cone wall surface area as possible (increasing the area where the laser can interact with the wall with a slight angle) is the reason for the observed proton energy enhancement. The knowledge obtained from these series of experiments, supported by the numerical simulations, will help us understand the fundamental laser-cone interaction, and develop new, more efficient targets, hopefully yielding even higher proton energy. __________________________________________________[1] K. A. Flippo, E. d'Humières, S. A. Gaillard, J. Rassuchine, D. C. Gautier, M. Schollmeier, F. Nürnberg, J. L. Kline, J. Adams, B. Albright, M. Bakeman, K. Harres, R. P. Johnson, G. Korgan, S. Letzring, S. Malekos, N. Renard-Le Galloudec, Y. Sentoku, T. Shimada, M. Roth, T. E. Cowan, J. C. Fernández, and B. M. Hegelich, Increased Efficiency of Short-Pulse Laser Generated Proton Beams from Novel Flat-Top Cone Targets, Physics of Plasmas (Invited) 15, 5 (2008).[2] S. A. Gaillard, K. A. Flippo, M. E. Lowenstern, J. E. Mucino, J. M. Rassuchine, D. C. Gautier, J. Workman, and T. E. Cowan, Proton acceleration from ultra high-intensity short-pulse laser-matter interactions with Cu micro-cone targets at the intrinsic ~10-8 contrast, submitted to Journal of Physics Conference Series (JPCS) (2009).[3] J. Rassuchine, E. d'Humières, S. D. Baton, P. Guillou, M. Koenig, M. Chahid, F. Pérez, J. Fuchs, P. Audebert, R. Kodama, M. Nakatsutsumi, N. Ozaki, D. Batani, A. Morace, R. Redaelli, L. Grémillet, C. Rousseaux, F. Dorchies, C. Fourment, J. J. Santos, J. Adams, G. Korgan, S. Malekos, S. B. Hansen, R. Shepherd, K. Flippo, S. Gaillard, Y. Sentoku, and T. E. Cowan, Enhanced hot electron localization and heating in high-contrast ultra-intense laser irradiation of sharp micro-cone targets, Physical Review E 79, 0364408 (2009).[4] S. D. Baton, M. Koenig, J. Fuchs, A. Benuzzi-Mounaix, P. Guillou, B. Loupias, T. Vinci, L. Grémillet, C. Rousseaux, M. Drouin, E. Lefebvre, F. Dorchies, C. Fourment, J. J. Santos, D. Batani, A. Morace, R. Redaelli, M. Nakatsutsumi, R. Kodama, A. Nishida, N. Ozaki, T. Norimatsu, Y. Aglitskiy, S. Atzeni, and A. Schiavi, Inhibition of fast electron energy deposition due to preplasma filling of cone-attached targets, Physics of Plasmas 15, 042706 (2008).[5] S. A. Gaillard, T. Kluge, K. A. Flippo, B. Gall, T. Lockard, M. Schollmeier, M. Geissel, D. T. Offermann, J. M. Rassuchine, D. C. Gautier, E. d'Humières, M. Bussmann, Y. Sentoku, and T. E. Cowan, Increased proton energies up to 67.5 MeV from high-contrast high-intensity short-pulse laser-interactions with micro-cone targets, in preparation (2010).[6] (a) R. Snavely, M. Key, S. Hatchett, T. Cowan, M. Roth, T. Phillips, M. Stoyer, E. Henry, T. Sangser, M. Signh, S. Wilks, A. Mackinnon, A. Offenberger, D. Pennington, K. Yasuike, A. Langdon, B. Lasinski, J. Johnson, M. Perry, and E. Campbell, Intense high-energy proton beams from petawatt-laser irradiation of solids, Physical Review Letters 85, 2945 (2000).(b) S. P. Hatchett, C. G. Brown, T. E. Cowan, E. A. Henry, J. S. Johnson, M. H. Key, J. A. Koch, A. B. Langdon, B. F. Lasinski, R. W. Lee, A. J. Mackinnon, D. M. Pennington, M. D. Perry, T. W. Phillips, M. Roth, T. C. Sangster, M. S. Singh, R. A. Snavely, M. A. Stoyer, S. C. Wilks, and K. Yasuike, Electron, photon, and ion beams from the relativistic interaction of petawatt laser pulses with solid targets, Physics of Plasmas 7, 2076 (2000)

Tissue mimicking materials for imaging and therapy phantoms: a review

Tissue mimicking materials (TMMs), typically contained within phantoms, have been used for many decades in both imaging and therapeutic applications. This review investigates the specifications that are typically being used in development of the latest TMMs. The imaging modalities that have been investigated focus around CT, mammography, SPECT, PET, MRI and ultrasound. Therapeutic applications discussed within the review include radiotherapy, thermal therapy and surgical applications. A number of modalities were not reviewed including optical spectroscopy, optical imaging and planar x-rays. The emergence of image guided interventions and multimodality imaging have placed an increasing demand on the number of specifications on the latest TMMs. Material specification standards are available in some imaging areas such as ultrasound. It is recommended that this should be replicated for other imaging and therapeutic modalities. Materials used within phantoms have been reviewed for a series of imaging and therapeutic applications with the potential to become a testbed for cross-fertilization of materials across modalities. Deformation, texture, multimodality imaging and perfusion are common themes that are currently under development

Development and performance evaluation of detectors in a Compton camera arrangement for ion beam range monitoring in particle therapy

The growing interest in particle beam therapy for cancer treatment is driven by the ability to provide high precision dose delivery. However, this benefit demands a high accuracy on the determination of the well-localized dose deposition (Bragg peak), which has to be located within the tumor volume. Different approaches for the beam range monitoring are worldwide being evaluated. The Compton camera is one of the proposed techniques, which aims at providing real-time, in-vivo proton (or ion) beam range monitoring by means of the detection of secondary prompt gamma rays, resulting from nuclear reactions between the particle beam and the biological tissue. The purpose of our project is to develop and commission an imaging system based on a Compton camera detector arrangement which could monitor in (ultimately) real-time the ion beam range. In the context of this thesis a Compton camera detector prototype was characterized, consolidated and commissioned with both a multi-layer and a mono-layer scatter component. The first detector arrangement belongs to the LMU Compton camera: the detector components were extensively characterized in order to determine the limitations imposed by their internal structure and the required configuration for an optimum performance. The complexity of the signal readout and processing could be reduced in view of facilitating an envisaged clinical applicability of the system. The scatter component (tracker) is formed by a stack of six highly segmented double-sided Si-strip detectors, whereas a monolithic LaBr3(Ce) scintillator (5 x 5 x 3 cm3) acts as the absorber component and is coupled to a segmented position-sensitive multi-anode photomultiplier tube (PMT). The initially applied 256-fold segmented PMT was replaced by a 64-fold segmented PMT, and similar or even superior performance was demonstrated for the latter one. The same trend of an improving spatial resolution, with an increasing energy of the incoming photon, which was observed when using the 256-fold segmented PMT, was also preserved: at 137Cs energy a value of 3.4(1) mm was obtained, while at the 1173 keV and 1332 keV 60Co photopeaks the spatial resolution reached values of 2.9(1) mm, thus below the 3 mm absorber resolution envisaged by the Compton camera design. Moreover, first tests in view of a possible replacement of the LaBr3(Ce) scintillation material with the cost-effective and radio-pure CeBr3 scintillator material were pursued and seem promising (ΔE/E ≃ 4% at 662 keV and comparable timing properties as LaBr3(Ce)). The signal processing and data readout system for the scatter component was upgraded from an ASIC-based electronics to a more flexible and higher performing electronics based on discrete components. Full compliance of the new frontend electronics with the detector signal specifications of our camera prototype was achieved: an acceptance of both signal polarities was introduced as well as a trigger capability for the scatter component, which previously did not exist. Furthermore, the upgrade of the signal processing and data acquisition was extended to the whole Compton camera setup, adapting the new frontend electronics designed initially for replacing the outdated ASIC-based modules of the scatterer also to the signal properties of the absorber scintillator and its segmented readout. This allowed for reducing the complexity of the system and finally achieve a 1 Mcps count rate capability as required in a clinical scenario: the VME-based readout modules were implemented into the new DAQ software and the data streams of scatterer and absorber were merged. The reduced granularity of the PMT signal channels combined with the use of the new signal processing and data acquisition system based on optical fibers makes the Compton camera setup less complex and more flexible. All detectors can be mounted in a newly designed Faraday cage, which includes also an active cooling, capable of reducing the dark current in the silicon detectors. The upgraded system was tested in the laboratory as well as under online conditions with particle beams at the Tandem accelerator in Garching. A validation with high energy prompt-γ rays was performed, bombarding water and PMMA targets with a 20 MeV proton beam and the same detector performance could be demonstrated also with the new signal processing system. The achievable trigger rate was increased by one order of magnitude and due to the efficient selection of Compton scattered events by triggering on the scatter component, the ratio of registered Compton events could be increased by about three orders of magnitude compared to the previous data acquisition system. The camera system was also tested by hitting a water target with a pulsed deuteron beam in order to allow for assessing the timing performance. With an envisaged improved version of the internal implantation structure of the segmented silicon scatter modules, the multi-layer Compton camera system will be ready for a full performance characterization of the imaging system's capabilities. By using the high performing LaBr3(Ce) monolithic scintillator as absorber, a Compton camera setup was also arranged with a mono-layer scattering component consisting of a pixelated 22 x 22 array of GAGG scintillator crystals. A proof of principle study was carried out using 137Cs and 60Co calibration sources: the source position reconstruction was performed with the MEGAlib software and the resulting reconstructed images from experimental data were compared to images reconstructed from simulated data. A source shift of 2 mm could be resolved by the system with sub-millimeter accuracy. A trend of improving angular resolution with the incoming photon energy reflects the detectors' (energy and spatial resolution) performance improvements with increasing energy. The system was characterized in different geometrical configurations, in order to address not only a possible prompt-gamma imaging application, but also a multi-modality detector system able to be applied also in PET- or gamma-PET-like imaging scenarios

Particle Physics Reference Library

This second open access volume of the handbook series deals with detectors, large experimental facilities and data handling, both for accelerator and non-accelerator based experiments. It also covers applications in medicine and life sciences. A joint CERN-Springer initiative, the “Particle Physics Reference Library” provides revised and updated contributions based on previously published material in the well-known Landolt-Boernstein series on particle physics, accelerators and detectors (volumes 21A,B1,B2,C), which took stock of the field approximately one decade ago. Central to this new initiative is publication under full open access