Particle therapy exploits the energy deposition pattern of hadron beams. The narrow Bragg Peak at the end of range is a major advantage but range uncertainties can cause severe damage and require ...online verification to maximise the effectiveness in clinics. In-beam Positron Emission Tomography (PET) is a non-invasive, promising in-vivo technique, which consists in the measurement of the β+ activity induced by beam-tissue interactions during treatment, and presents the highest correlation of the measured activity distribution with the deposited dose, since it is not much influenced by biological washout. Here we report the first clinical results obtained with a state-of-the-art in-beam PET scanner, with on-the-fly reconstruction of the activity distribution during irradiation. An automated time-resolved quantitative analysis was tested on a lacrimal gland carcinoma case, monitored during two consecutive treatment sessions. The 3D activity map was reconstructed every 10 s, with an average delay between beam delivery and image availability of about 6 s. The correlation coefficient of 3D activity maps for the two sessions (above 0.9 after 120 s) and the range agreement (within 1 mm) prove the suitability of in-beam PET for online range verification during treatment, a crucial step towards adaptive strategies in particle therapy.
Solid-state photo-detectors are one of the main innovations of past century in the field of sensors. First produced in the early forties with the invention of the p–n junction in silicon and the ...study of its optical properties, photo-detectors received a major boost in the sixties when the p-i-n (PIN) photodiode was developed and successfully used in several applications.
The development of devices with internal gain, avalanche photodiodes (APD) first and then Geiger-mode avalanche photodiodes, named single photon avalanche diode (SPAD), leads to a substantial improvement in sensitivity and allowed single photon detection. Later on, thousands of SPADs have been assembled in arrays of few millimeters squared (named SiPM, silicon photo-multiplier) with single photon resolution.
The high internal gain of SiPMs, together with other features peculiar of the silicon technology like compactness, speed and compatibility with magnetic fields, promoted SiPMs as the principal photo-detector competitor of photomultipliers in many applications from radiation detection to medical imaging.
This paper provides a review of the properties of analog solid-state photo-detectors. Particular emphasis is given to latest advances on Positron Emission Tomography instrumentation boosted by the adoption of the silicon photo-detectors as an alternative to photomultiplier tubes (PMTs). Special attention is dedicated to the SiPMs, which are playing a key role in the development of innovative scanners.
The TRIMAGE project aims at developing a brain-dedicated PET/MR/EEG system able to perform simultaneous PET, MR, and EEG acquisitions for application in schizophrenia. Both PET and MR components have ...been designed in this project. The PET component consists of a full ring with 18 sectors each comprising three square detector modules. The modules are based on dual-layer staggered matrices of LYSO crystals read out by silicon photomultipliers. This paper describes in full detail the final version of the PET detectors and the related electronics. It also reports on the preliminary performance of a pair of sectors in terms of pixel resolvability index (RI), energy resolution, singles count rate capability, and coincidence time resolution (CTR). The procedures used for the optimization and calibration of PET detector are described. Results demonstrate the pixel/layer identification performance with an RI of about 0.2 while the energy resolution resulted in 20% and 22% FWHM for the bottom and top layer, respectively. The maximum singles count rate of a PET detector is about 700 kcps and the CTR of two sectors is 515 ps.
Medical applications of silicon photomultipliers Bisogni, Maria Giuseppina; Del Guerra, Alberto; Belcari, Nicola
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
05/2019, Volume:
926
Journal Article
Peer reviewed
Open access
Silicon photomultipliers (SiPMs) are becoming the reference photodetectors in many fields. In medicine they are slowly replacing photomultiplier tubes and avalanche photodiodes in medical imaging and ...in PET in particular. In this paper a broad overview of the current applications of SiPM in medicine is presented. The major fields where the SiPMs are used, namely PET/MR and hadrontherapy are discussed at length.
The quality assurance of particle therapy treatment is a fundamental issue that can be addressed by developing reliable monitoring techniques and indicators of the treatment plan correctness. Among ...the available imaging techniques, positron emission tomography (PET) has long been investigated and then clinically applied to proton and carbon beams. In 2013, the Innovative Solutions for Dosimetry in Hadrontherapy (INSIDE) collaboration proposed an innovative bimodal imaging concept that combines an in-beam PET scanner with a tracking system for charged particle imaging. This paper presents the general architecture of the INSIDE project but focuses on the in-beam PET scanner that has been designed to reconstruct the particles range with millimetric resolution within a fraction of the dose delivered in a treatment of head and neck tumors. The in-beam PET scanner has been recently installed at the Italian National Center of Oncologic Hadrontherapy (CNAO) in Pavia, Italy, and the commissioning phase has just started. The results of the first beam test with clinical proton beams on phantoms clearly show the capability of the in-beam PET to operate during the irradiation delivery and to reconstruct on-line the beam-induced activity map. The accuracy in the activity distal fall-off determination is millimetric for therapeutic doses.
•The free-electrons-fraction is the fraction of the electrons generated that are collected without attachment.•The method proposed is based only from measure of charge collected varying the voltage ...applied.•The method proposed can be use in the commissioning phase of a dedicated to the Flash radiotherapy Linac.
The free electron fraction is the fraction of electrons, produced inside the cavity of an ionization chamber after irradiation, which does not bind to gas molecules and thereby reaches the electrode as free electrons. It is a fundamental quantity to describe the recombination processes of an ionization chamber, as it generates a gap of positive charges compared to negative ones, which certainly will not undergo recombination.
The free electron fraction depends on the specific chamber geometry, the polarizing applied voltage and the gas thermodynamic properties. Therefore, it is necessary to evaluate such fraction in an accurate and easy way for any measurement condition.
In this paper, a simple and direct method for evaluating the free electron fraction of ionization chambers is proposed.
We first model the capture process of the electrons produced inside an ionization chamber after the beam pulse; then we present a method to evaluate the free electron fraction based on simple measurements of collected charge, by varying the applied voltage. Finally, the results obtained using an Advanced Markus chamber irradiated with a Flash Radiotherapy dedicated research Linac (ElectronFlash) to estimate the free electron fraction are presented.
The proposed method allows the use of a conventional ionization chamber for measurements in ultra-high-dose-per-pulse (UHDP) conditions, up to values of dose-per-pulse at which the perturbation of the electric field due to the generated charge can be considered negligible.
Silicon Photomultipliers (SiPM) as novel photodetectors for PET Del Guerra, Alberto; Belcari, Nicola; Giuseppina Bisogni, Maria ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
08/2011, Volume:
648
Journal Article
Peer reviewed
Open access
Next generation PET scanners should fulfill very high requirements in terms of spatial, energy and timing resolution. Modern scanner performances are inherently limited by the use of standard ...photomultiplier tubes. The use of Silicon Photomultipliers (SiPMs) is proposed for the construction of a 4D-PET module of 4.8×4.8
cm
2 aimed to replace the standard PMT based PET block detector. The module will be based on a LYSO continuous crystal read on two faces by Silicon Photomultipliers. A high granularity detection surface made by SiPM matrices of 1.5
mm pitch will be used for the
x–
y photon hit position determination with submillimetric accuracy, while a low granularity surface constituted by 16
mm
2 SiPM pixels will provide the fast timing information (
t) that will be used to implement the Time of Flight technique (TOF). The spatial information collected by the two detector layers will be combined in order to measure the Depth of Interaction (DOI) of each event (
z).
The use of large area multi-pixel Silicon Photomultiplier (SiPM) detectors requires the development of a multichannel Data Acquisition system (DAQ) as well as of a dedicated front-end in order not to degrade the intrinsic detector capabilities and to manage many channels. The paper describes the progress made on the development of the proof of principle module under construction at the University of Pisa.
Development of a PET detector module with Depth of Interaction capability Morrocchi, Matteo; Ambrosi, Giovanni; Giuseppina Bisogni, Maria ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
12/2013, Volume:
732
Journal Article
Peer reviewed
The 4DM-PET experiment aims to develop an innovative detector module for PET applications. The device is composed of a continuous LYSO scintillator crystal coupled to two SiPM matrices on its top and ...bottom surfaces. The peculiarity in using a continuous crystal is the ability to reconstruct the Depth of Interaction of the 511keV photons generated by the annihilation of the positrons emitted by the radiotracer. A first small prototype module has been built. It is composed of a LYSO crystal, 20×20×10mm3 coupled on larger surfaces with arrays of SiPMs (4×4pixel, 4×4mm2 each). The lateral faces of the crystal slab are black painted to avoid reflection of light. The detector is read by custom designed Front-End ASICs. We have scanned the detector in the three coordinates with pencil beams produced by collimated radioactive sources in order to investigate the module spatial resolution capabilities. The results achieved in terms of Depth of Interaction (DOI) reconstruction and Point Spread Function (PSF) at different positions on the detector surface are presented.
Silicon photomultipliers (SiPM) are a novel type of photodetectors that show great promise for nuclear medicine applications and especially for the next generation of PET scanners. The INFN ...collaboration DASIPM2 is investigating in depth the properties of the SiPM developed at FBK-irst (Trento, Italy), whose performance compete successfully with those of similar devices produced by commercial companies, but have in addition novel and attractive properties, such as monolithic matrix arrangement. In this paper we illustrate the advantages and pitfalls of the SiPM for PET applications. In particular we report on the most recent experimental results for SiPM and SiPM matrices performances: (i) an intrinsic very good time resolution that coupled to a high PDE could favor time-of-flight PET exploitation; (ii) very high photodetector granularity that allows position determination with continuous crystal and possibly stacking of several layers, i.e., Depth Of Interaction information capability thus paving the way for the construction for the next generation of PET cameras; (iii) MRI compatibility in magnetic field and magnetic field gradient, thus giving the possibility of constructing a state-of-the-art PET insert within an MRI scanner.
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