123: Multigap Resistive Plate Chambers as a Positron Emission Tomography detector

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ICTR-PHE – 2014

- Beam intensity: 3.108 protons.s-1 - Physical dose: 1 Gy - Target: PMMA - Range modulation: 3.5-6.5 cm - Energy modulation: 69.4-98.7 MeV - Total number of primary protons: 42.109 - Irradiation time: 14 s Only the 14 s irradiation period was considered, in order to fully exploit the induced β+ activity available for an in-beam PET acquisition. Different detector geometries have been considered in order to investigate the impact of PET sensitivity. Results: We have identified an objective trigger criterion which allows selection of true coincidences coming from β + annihilation based on the knowledge of the beam position. Thanks to the know-how acquired from high energy physics, we are currently developing an in-beam PET device based on fast analogue sampling modules and multiple layer trigger using µTCA standard. Such technology is able to handle a large flow of data and process them quickly thanks to the serial backplanes and high-speed busses provided by µTCA standard. Conclusion: It appears feasible to implement such trigger condition into a dedicated µTCA serial point-to-point topology. This would provide a fast data acquisition system with low dead-time, able to reject nuclear induced false coincidences.

layer has 2x64 strips with a pitch of 1.41 mm. Dedicated electronic-readout systems have been designed at IPNL and LPC for the three detection systems. A micro-TCA acquisition system is under development. Single and coincidence rates have been measured at HIT (Germany), with 160 MeV protons and 311 MeV/u carbon ions impinging on a cylindrical PMMA phantom (diameter 15 cm, length 20 cm) with the intention to assess the simulation predictions and to scale real signal and background count rates. In order to simulate coincidence rates with GEANT4, the time structure of an IBA cyclotron has been modeled (ion bunches every ~10 ns in the case of protons). Results: Single and coincidence rates provided by simulations are in good agreement with measurements. For a discussion of the clinical applicability of the Compton camera, the prompt gamma profiles of real to random coincidences have been analyzed. We also present the different detector developments together with their associated electronics. Conclusions: The simulations and the experiments give us a preliminary idea of the applicability of the Compton camera in hadrontherapy. Further tests are now required to scale up the prototype for clinical conditions.

Keywords: in-beam PET, particle therapy, range verification

References: [1] A.-C. Knopf and A. Lomax, Phys. Med. Biol. 58 (2013) R131–R160 [2] S.W. Peterson et al., Phys. Med. Biol. 55 (2010) 6841– 6856 [3] G. Llosa et al., NIMA 695(2012)105–108 [4] T. Kormoll et al., IEEE-TNS (2011) 3484 - 3487 [5] S. Kurosawa et al., Current Applied Physics 12 (2012) 364-368 [6] F. Roellinghoff et al. NIM A 648 (2011) S20

122 Development of a Time-Of-Flight Compton Camera for Online Control of Ion Therapy J.-L. Ley1, M. Dahoumane1, D. Dauvergne1, N. Freud2, B. Joly3, J. Krimmer1, J.M. Létang2, L. Lestand3, H. Mathez1, G. Montarou3, C. Ray1, M-.H. Richard1, E. Testa1, Y. Zoccarato1 1 Université de Lyon, Université Claude Bernard Lyon 1, CNRS/IN2P3, Institut de Physique Nucléaire de Lyon, 69622 Villeurbanne; MICRHAU pôle de Microélectronique Rhône Auvergne, France 2 Université de Lyon, CREATIS; CNRS UMR5220; Inserm U1044; INSA - Lyon; Université Lyon 1; Centre Léon Bérard, France 3 Laboratoire de Physique Corpusculaire de ClermontFerrand, France Purpose: The aim of irradiation monitoring during a treatment in ion therapy is to control in real time the agreement between the delivered dose and the planned treatment. In fact, the discrepancies might come from uncertainties such as the planning accuracy by itself, or by variations due to the positioning or the anatomical changes of the patient. This can lead to ion-range variations of a few millimeters. Several devices are under development over the world to detect secondary radiations, which are correlated to the dose deposited by incident ions [1]. Compton cameras are in particular investigated for their potential high efficiency to detect prompt-gammas [2-5]. The present work aims at discussing the clinical applicability of a Compton camera design by means of Monte Carlo simulations validated against measurements of single and coincidence rates. Materials/methods: A Compton camera with electronic collimation was designed by GEANT4 9.4 simulations, in order to optimize the detection of prompt gammas and to discriminate the neutrons by the time of flight [6]. According to the Monte Carlo design, a prototype, which is composed of three parts, is under development: a hodoscope (2x128 square scintillating fibers), a scatterer and an absorber (100 blocks of streaked BGO of 38x35x30 mm3). The hodoscope is used to tag the incidents ions in time and position. The scatterer is a stack of seven doublesided silicon strip detectors of 90x90x2 mm3. Each silicon

Keywords: hadrontherapy, Compton camera

online

ion

range

control,

123 Multigap Resistive Plate Chambers as a Positron Emission Tomography detector L. Litov1, G. Georgiev1, V. Kozhuharov1, N. Ilieva2, B. Pavlov1, P. Petkov1 1 University of Sofia St. Kliment Ohridski, Bulgaria 2 Institute for Nuclear Research and Nuclear Energy, Bulgaria The Resistive Plate Chambers (RPC) are gaseous parallel plate detectors for charged particles that are widely used in largescale high energy physics experiments as fast trigger detectors for muon spectrometers. The RPC’s main advantages are the high time and spatial resolution and their ability to work in strong magnetic fields. RPC technology allows building a device with a large field of view, increasing drastically the geometrical acceptance in comparison to the standard PET devices. The RPC’s excellent position resolution for the gamma quanta impact point and the time-of-flight measurement accuracy will allow reconstruction of the image with precision better than 1 mm. Transforming the resistive plate chambers from charged-particle into gamma-quanta detectors opens the way towards their application as a basic element of a hybrid imaging system, which combines positron emission tomography (PET) with magnetic resonance imaging (MRI) in a single device. The detector design is chosen after detailed GEANT based simulations. Special care is taken to decrease the registration efficiency for Compton scattered photons, while keeping relatively high efficiency for 511 keV photons. The detector photon efficiency paint layer on the resistive plates. This layer increases photons-to-electrons conversion probability and thus the detector efficiency. Compton suppression is achieved by

ICTR-PHE – 2014 adding a layer of floating glass on the lead paint. The glass acts as a filter, preventing low energy electrons to enter the active gas volume. Successful Compton suppression is crucial for the construction of RPC-based PET detectors. Detector prototypes have been build and tested using cosmic muons and 22Na source. The RPCs working in avalanche mode with a Freon-based gas mixture are coupled to front-end electronics, used by the CMS experiment and the signals are fed to a custom made DAQ board or to a fast TDC. A LYSO crystal coupled to SiPM is used to trigger on 511 keV photons. We present results towards the development of a hybrid imaging system based on multigap glass resistive plate chambers. It is show that a stack of multigap RPC detector modules could achieve efficiency for 511 keV photons up to 30% and could ensure signal-to-background ratio (511 keV photons to photons with energies below 380 keV) better than 6:1. We present also test results for the performance and stability of a single multigap RPC module. The results from the tests are in a good agreement with the simulation predictions and justify the next step – investigation of a full-size single-stack prototype in MRI environment. Keywords: PET-MRI, Resistive Plate Chambers 124 Ongoing investigations on ion-based radiography and tomography L. Magallanes1,2, V. Bernd3, S. Brons4, O. Jäkel1,4, K. 1,2 1,2 3 Parodi , I. Rinaldi , M. Takechi 1 Department of Radiation therapy and Radiation Oncology, Heidelberg University Clinic, Heidelberg, Germany 2 Ludwig Maximilians University Munich, Munich, Germany 3 GSI Helmholtz Center for Heavy Ion Research, Darmstadt, Germany 4 Heidelberg University Clinic and German Cancer Research Center, Heidelberg, Germany Purpose: The major advantage of ion therapy is the conformal dose distribution with the characteristic inverted depth dose profile (Bragg peak) and the finite ion beam range. However, full therapeutic exploitation of ion beams requires a precise determination of the distal dose fall-off in the tissue, which is currently challenged by major range uncertainties. Innovative imaging techniques have to be integrated in the ion beam therapy work-flow in order to minimize such uncertainties. Ion-based transmission imaging (radiography and tomography) is suitable to be applied at different stages of the treatment work-flow. During the planning phase, the distribution of the relative stopping power can be reconstructed and introduced as input of the treatment planning system. Moreover, during the delivery phase, transmitted planar or volumetric images can be used in-vivo and prior to treatment for confirming patient anatomy/position and range verification. Materials and methods: The investigated imaging modality relies on ion beams at higher energy and lower fluence than therapeutically used, so that the transmitted ions can be detected after they exit the phantom, thus providing information on the residual beam range. To this aim, a prototype detector system consisting of a stack of 61 parallel ionization chambers with PMMA absorber plates, which was originally assembled at GSI Helmholtz Center for Heavy Ion Research for dosimetric purposes, has been slightly modified. The setup is being characterized with carbon ion beams at the Heidelberg Ion Beam Therapy Center to assess its potential use in ion-based transmission imaging. The ongoing experimental investigations are supported by Monte Carlo simulations. Results: The experiments carried out with energetic, low scattering, carbon ion beams show promising images of phantoms of different complexity and composition. A

S61 detailed characterization of the detector, in terms of setup and read-out electronics, has been completed. It revealed the importance of further optimization of the actual detector system, supported by Monte Carlo simulations, to improve image resolution, efficiency of fast data acquisition and image reconstruction, towards the potential application in the clinical routine. Conclusions: This contribution will present the status and outlook of the ion-based radiographic and tomographic imaging technique which is being developed in the framework of a joint project between the University Clinic in Heidelberg, the Ludwig-Maximilians University in Munich and the GSI Helmholtz Center for Heavy Ion Research. Keywords: ion-based transmission imaging, ion radiography/ tomography 125 Interstitial Detectors for Synchronized Radiation Quality and Range Verification in Ion-Beam Therapy G. Magrin1, L. Grevillot1, M. Dominietto2, R. Mayer1 1 EBG MedAustron, Wiener Neustadt, Austria 2 ETH Zurich Purpose: The accurate conformation of the dose to the tumor volume and the detailed characterization of the biological effectiveness are important challenges of ion-beam therapy that still need to be fully addressed. A poor performance in fulfilling one or both results in an un-necessary dose delivered to healthy tissue and organs at risk. The single-event-energy-deposition spectra (microdosimetry) are continuously modified when the beam penetrates the tissue and the most drastic changes are located in the region of the Bragg peak (for both, protons and carbon ions). Combining the spectrum information with measurements of dose will virtually make it possible to recreate the Bragg peak, or at least a fraction of it, in the region close to the detector. A feasible result is the estimation of residual range when the device is placed in the distal part of the tumor. Non-standard microdosimeters inserted in the irradiated region during treatment could perform this task maintaining also the capability of estimating the biological effectiveness. Materials/methods: Single crystal chemical vapor deposition (SC-CVD) diamonds with tissue equivalent thickness ranging from 0.8 to 18.7 µm were developed and tested in the framework collaborations of MedAustron and INFN Tor Vergata and Legnaro, AIT, and ENEA with alpha radiation of 5.5 MeV and below. Monte Carlo simulations (Fluka and Gate/Geant4) supported the design of superficial and interstitial radiation detectors for the characterization of the radiation in terms of quality and of absorbed dose. Ex-vivo studies to assess the compatibility of the detectors with biological tissue and magnetic resonance imaging (MRI) have been initiated in collaboration with ETHZ. Results: SC-CVD diamonds have been simulated to optimize their characteristics of thickness and transversal section and improve the performances. A self-calibration method has been identified. Measurements with alpha particles and calibrated gold absorbers have been done using different diamond prototypes. The feasibility of miniaturizing the device has been verified by manufacturing detectors with sensitive volumes of 150 µm in diameter and 230 nm in thickness and reaching virtually 100% of charge collection efficiency for lineal energies over 60 keV/um. Animal studies proved the compatibility of the device with MRI and gave preliminary indication for physiological compatibility. Conclusions: The devices based on SC-CVD diamond have shown compatibility with interstitial measurement of dose and parameters which can be associated to radiation quality