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Imaging in Radiation Therapy and New Detector Technology

Session chair: Gonzalez Montoro , Andrea (Stanford University, Department of Radiology, Stanford, USA); Schaart , Dennis R. (Delft University of Technology, Medical Physics & Technology, Delft, Netherlands)
Shortcut: M-01
Date: Wednesday, 20 October, 2021, 7:00 AM - 8:45 AM
Room: MIC - 1
Session type: MIC Session


Click on an contribution to preview the abstract content.

7:00 AM M-01-01

Experimental characterization and test-beam results of MACACO III Compton camera (#812)

L. Barrientos1, M. Borja-Lloret1, J. V. Casaña1, J. García Lopez2, F. Hueso-González1, M. D. C. Jiménez-Ramos2, E. Muñoz1, A. Ros1, J. Roser1, C. Senra1, R. Viegas1, G. Llosá1

1 IFIC (CSIC-University of Valencia), Valencia, Spain
2 Centro Nacional de Aceleradores (Universidad de Sevilla, CSIC and Junta de Andalucía), Sevilla, Spain


The IRIS group at IFIC-Valencia is developing a Compton camera prototype with the aim of applying it in hadron therapy treatment monitoring. Recently, a third version of the prototype MACACO (Medical Applications CompAct COmpton camera) has been built. The system is composed of three Lanthanum (III) bromide scintillator crystals coupled to silicon photomultipliers. To improve its performance for the final application, several detectors are tested, two different silicon photomultipliers (25 and 50 μm) have been chosen as possible candidates. The 25 μm photodetector provided better performance in terms of dynamic range, energy resolution (5.2% FWHM at 511 keV) and stability with temperature variations. MACACO III has also been tested in the CNA cyclotron (Seville) with 18 MeV proton beam to produce 4.439 MeV gamma rays. Data have been acquired with a graphite target in five different positions at 2.5 nA nominal beam intensity. Images with 4.439 MeV photons have been reconstructed, demonstrating the system capability to reconstruct images at energies relevant for hadron therapy. Moreover, the system has been able to distinguish 1 mm displacements in the target position.

Keywords: Compton camera, hadron therapy treatment monitoring, Lanthanum (III) bromide, silicon photomultipliers, proton beam
7:15 AM M-01-02

The iMPACT achromatic calorimeter for proton Computed Tomography (#1274)

P. Giubilato1, 2, S. Mattiazzo4, 2, F. Baruffaldi1, 2, D. Chiappara1, 2, J. Wyss3, 2, D. Pantano1, 2

1 University of Padova, Physics and Astronomy, Padua, Italy
2 INFN, Padova, Padua, Italy
3 University of CAssino, Engineering, Cassino, Italy
4 University of Bergamo, Physics, Bergamo, Italy


The iMPACT (innovative Medical Protons Achromatic Calorimeter and Tracker) ERC funded project aims developing a fast scanner for proton Computed Tomography (pCT) using protons in the 200 – 300 MeV energy range. The goal is to accurately record the track and energy of 109 particles in less than 10 s over an area of about 100 cm2, even when using pencil-scan beams, allowing to promote the pCT technique from the research field to the real medical application world.

This contribution focuses on the calorimeter, which is a range design composed by almost 1000 independent scintillating elements, each having a volume of about 0.5×1×20 cm3, arranged in a 3D orthogonal pattern. Each scintillator is coupled to a readout SiPM, which is sampled at high rate by a custom-made, 2 bit front-end digitizer to extrapolate the instantaneous particle dE/dx. The inherent system parallelism allows to handle high flux rates up to many tens MHz cm-2, making it compatible with the timing of typical pencil-beam found at proton and hadrons therapy facilities. The system is built from identical, modular basic elements, which allow easily tailoring its size to the expected particles energy range, making it easy to adapt it to other energy ranges, and/or entirely different applications.

We illustrates the calorimeter operating principles, design, and realization. Measurements of the single channel performance as well as the whole system are reported. A robust self-calibration procedure, necessary to effectively tune the gain of multiple channels, has been developed and will be discussed as well.

The iMPACT project is funded by the European Community ERC consolidator grant number 649031.
The ALPIDE sensor and its readout electronics has been developed by the ALICE international collaboration.
The irradiation facility used for part of the test beams is managed by the Trento ATREP institute, and the staffs who did help to set up and run the test beam belong to the ATREP and TIFPA institutes.

Keywords: calorimeter, hadroteraphy, proton Computed Tomography, scintillators, SiPM
7:30 AM M-01-03

A portable gamma camera for the optimization of the patient dosimetry in radioiodine therapy of thyroid diseases (#1111)

T. Bossis1, M. - A. Verdier1, 4, L. Pinot1, F. Bouvet1, T. Beaumont2, D. Broggio2, S. Lamart2, O. Caselles3, S. Zerdoud3, L. Menard1, 4

1 IJCLab-Universite Paris-Saclay, CNRS-IN2P3, ORSAY, France
4 Université de Paris, PARIS, France


Molecular radiotherapy is an efficient treatment modality of benign and malign thyroid diseases. However, there is still a need to better assess the dose delivered to target tissues and organs-at-risk in order to optimize for each patient the activity to be administered according to the objectives of disease control (destruction of tumor residues, restoration of thyroid function or hypothyroidism) while maintaining the risk of toxicity at a justifiable level. In that context, our objective is to develop a high-resolution mobile gamma camera specifically designed to accurately measure the radiotracer biokinetics at the patient's bedside during treatment planning and therapeutic dose verification. A first feasibility prototype of the mobile camera with a 5x5 cm2 field of view was developed for the treatment of benign and malign thyroid diseases with 131I, leading to promising results. We are currently developing a new prototype for clinical use with extended field of view (10x10 cm2). It consist of a 3D-printed parallel-hole tungsten collimator coupled to a 1 cm thick CeBr3 scintillator, readout by an array of 6x6 mm2 Silicon Photomultipliers. Preliminary results show a energy resolution of 7.1% and a FWHM spatial resolution around 1 mm at 356 keV. A detailed description of the camera optimisation (collimator and shielding design, intrinsic spatial performance, counting rate capabilities) will be presented.


With financial support from ITMO Cancer AVIESAN (Alliance Nationale pour les Sicences de la Vie et de la Santé/ National Alliance for Life Sciences & Health) within the framework of the Cancer Plan

Keywords: Internal radiotherapy, individualized dosimetry, miniaturized imaging device, thyroid deseases
7:45 AM M-01-04

Bismuth germanate (BGO) integrated microchannel plate photomultiplier tube (MCP-PMT) for direct positron emission imaging (dPEI) (#303)

S. I. Kwon1, R. Ota2, E. Berg1, T. Omura2, S. R. Cherry1

1 University of California, Davis, Biomedical Engineering, Davis, California, United States of America
2 Hamamatsu Photonics K. K., Central Research Laboratory, Hamamatsu, Japan


Positron emission tomography (PET) is a well-known imaging modality using positron-emitting radiotracers but must use tomographic reconstruction algorithms to produce cross-sectional images. However, once the timing resolution of detectors becomes sufficiently good to directly localize the source, we enter a new regime, in which an image can be directly obtained by measuring the difference in arrival time of the two 511 keV photons without any reconstruction. We refer to this new modality as direct positron emission imaging (dPEI). We recently demonstrated reconstruction-free cross-sectional imaging of positron-emitting radiotracers using two lead-glass (Cerenkov radiator) integrated MCP-PMTs (CRI-MCP-PMTs). However, the detector sensitivity must be increased in order to turn dPEI into a practical modality. In this study, we successfully developed a new CRI-MCP-PMT by replacing the current lead-glass entrance window with a bismuth germanate (BGO) entrance window, which has much higher stopping power and emits more Cerenkov photons than lead glass due to its high refractive index. The BGO integrated MCP-PMTs (BGO-MCP-PMTs) supply sufficient energy information for scatter rejection and achieved a superb coincidence timing resolution (CTR) of 80 ps FWHM. By integrating BGO as the window faceplate, instead of the traditional stacked detector design where the radiator is coupled to the photodetector through optical grease or glue, the integrated configuration provides a much higher probability to trigger on a prompt Cerenkov photon. We further improved timing resolution to 40 ps FWHM by coupling a SiPM on the BGO entrance window. This level of timing is sufficient to produce dPEI images with ~6 mm resolution.


Funding: NIH R35 CA197608, R01 EB029633, R03 EB027268. The authors thank Hideki Shimoi, Yutaka Hasegawa, Hiroji Nishizawa, Kenshi Shimano for fabricating the BGO-MCP-PMTs at Hamamatsu Photonics K.K. and Fondazione Bruno Kessler for providing the SiPMs and amplifiers.

Keywords: Bismuth germanate (BGO), microchannel plate photomultiplier tube (MCP-PMT), Cerenkov, direct positron emission imaging (dPEI), positron emission tomography (PET)
8:00 AM M-01-05

Scintillation Photon Counting Detectors with Analog Silicon Photomultipliers (#1377)

J. W. Cates1, W. - S. Choong2, E. Brubaker3

1 Lawrence Berkeley National Laboratory, Applied Nuclear Physics, Berkeley, California, United States of America
2 Lawrence Berkeley National Laboratory, Bioimaging, Berkeley, California, United States of America
3 Sandia National Laboratory, Livermore, California, United States of America


Standard signal processing approaches for scintillation detectors derive accurate estimates for radiation time of interaction and energy imparted to the detection media from aggregate characteristics of resultant electronic pulse shapes. The ultimate realization of a photosensor is one that provides a unique timestamp and position for each detected scintillation photon. Several novel works have highlighted how photosensors with these capabilities enable advanced concepts for 3D positioning and improved accuracy and robustness of time of interaction estimation with algorithms that exploit order statistics of individual scintillation photons, which can advance instrumentation performance across the applied sciences. Such detectors have been conceptualized and, to some degree, realized through the development digital silicon photomultipliers (dSiPMs). It is likely that ideal dSiPMs are available in the future, but there may be alternative approaches to achieve these goals today. In this work, we show that taking into consideration (1) the temporal photon density of a scintillator, (2) the channel density of arrays of analog SiPMs, (3) low noise, high frequency electronic readout, and (4) digital signal processing methodologies, scintillation detectors that uniquely count each scintillation photon can be realized. To demonstrate this novel approach, we constructed multichannel readout for a bismuth germanate (BGO)-based scintillation detector coupled to a 4x4 array SiPMs. With our first proof-of-concept measurements using this detector configuration, we are able to uniquely count and provide individual timestamps for ~80% of all optical photons. With this approach we can implement all “monolithic scintillator” 3D positioning and timing of interaction estimators which have been demonstrated or simulated for dSiPMs. We outline the methodology, electronics, and approach for achieving this detector capability and show proof-of-concept measurements for this technique.

Keywords: Photon Counting, scintillation detector
8:15 AM M-01-06

Metalens array faced to a multipixel photon counter for improved photodetection efficiency and single photon time resolution (#537)

S. Uenoyama1, R. Ota1

1 Hamamatsu Photonics K.K., Central Research Laboratory, Hamamatsu, Japan


Silicon photomultiplier (SiPM) is the most robust photodetector which can detect a single photon with excellent performance and has been widely used in several research topics, such as high energy physics experiments, light detection and ranging, and positron emission tomography. Photo detection efficiency (PDE) and single photon time resolution (SPTR) are representative characteristics which decide an SiPM performance. An SiPM typically has a trench structure which can successfully suppress an optical cross-talk between two independent micro cells. However, the trench structure not only reduces the PDE but also degrades the SPTR of the SiPM, consequently limiting the SiPM performance. In this study, we introduced a use of a metalens array which is faced to a multipixel photon counter (MPPC) to correct for the SiPM performance degradation caused by the trench structure. The array consists of 1584 metalenses whose sizes are 75  75 um2 corresponding to the micropixel pitch of the MPPC used in the experiment. The focused spot size of the metalens used in this study is approximately 1.0 um which is small enough to avoid the trench structure. Properly positioning the metalens array on the MPPC surface improved both the PDE and SPTR of the MPPC because the metalenses can guide optical photons only to the photosensitive area of the microcell while avoiding focusing on the trench area. As a result, we experimentally observed improvements in PDE and SPTR using a picosecond pulse laser (404 nm). Here, the overvoltage from the breakdown voltage of the MPPC was set to as low as 2.0 V to reduce dark count rate and cross-talk probability. We will increase statistics to evaluate the effect of the metalens more quantitatively. In addition, we will discuss feasibility of monolithically integrating the metalens array with the MPPC, and investigate performance of a metalens-integrated MPPC as a photodetector for radiation measurements.

Keywords: Metalens, Nanophotonics, MPPC, PDE, SPTR
8:30 AM M-01-07

Towards the ideal PET detector: a scalable architecture with high intrinsic spatial resolution, DOI and sub-200 ps TOF capability (#241)

G. Sportelli1, 2, M. G. Bisogni1, 2, C. Bruschini3, P. Carra1, 2, E. Charbon3, E. Ciarrocchi4, M. D'Inzeo5, K. Deprez7, G. Franchi5, F. Gramuglia3, M. Morrocchi1, 2, L. Perillo5, A. Puccini5, E. Ripiccini3, V. Rosso1, 2, M. Stockhoff6, 7, C. Thyssen6, 7, R. Van Holen6, 7, S. Vandenberghe6, 7, E. Vansteenkiste6, 7, N. Belcari1, 2

1 University of Pisa, Department of Physics, Pisa, Italy
2 Istituto Nazionale di Fisica Nucleare, Sezione di Pisa, Pisa, Italy
3 Ecole polytechnique fédérale de Lausanne, Lausanne, Vaud, Switzerland
4 University of Pisa, Department of Translational Research and of New Surgical and Medical Technologies, Pisa, Italy
5 AGE Scientific s.r.l., Capezzano Pianore (LU), Italy
6 University of Ghent, Ghent, Belgium
7 Molecubes N.V., Ghent, Belgium


A new PET detector prototype based on a monolithic LYSO crystal has been developed and characterised in the context of the UTOFPET project. The detector implements a distributed acquisition system and an AI-based processor that allows acquiring scintillation events from the outputs of 16 × 16 SiPMs at input rates that exceed 1 MHz. The SiPM outputs are read by 16 HRFlexToT ASICs and are digitised by an array of TDCs implemented on FPGA. An SoC-FPGA on the back of the detector runs a CNN that processes the outputs of the TDCs to generate the event position, time and energy. Event data are stored on a local memory and then transmitted offline to a host PC.
Laboratory tests using a 12 mm thick scintillator have shown that the detector is capable of an event positioning precision of 0.8 mm, a DOI of 1.4 mm FWHM, a coincidence timing resolution of 150 ps FWHM and an energy resolution of 11%. The obtained performance and the good scalability make the design suitable for applications ranging from small animal and dedicated organ imaging to clinical and total body PET.


The research leading to these results has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 688735 (Photonics Based Sensing ERA-NET Cofund), Regione Toscana and VLAIO.

Keywords: TOF-PET, monolithic scintillators, small animal imaging, total-body PET, artificial neural network

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