Search

In this paper, we investigate the use of a positron emission tomography (PET) system to monitor the proton therapy. The monitoring procedure is based on the comparison between the ${ \beta }+$ activity generated in the irradiated volume during the treatment, with the ${ \beta }+$ activity distribution obtained with Monte Carlo (MC) simulation. The dedicated PET system is a dual head detection system; each head is composed of nine scintillating LYSO crystal matrices read out independently with a custom modularized acquisition system. Our experimental data were acquired at the Cyclotron Centre Bronowice, Institute Nuclear Physics in Krakow, Poland, and were simulated with the FLUKA MC code. Homogeneous and heterogeneous plastic phantoms were irradiated with monoenergetic 130 MeV protons. The capabilities of our PET system to distinguish different irradiated materials were investigated, and the proton pencil-beams were used as probes. Our focus was to analyze the activity width and the total activity event number in several cases. Irradiations were performed using either single pencil-beams one at a time, or two pencil-beams during the same data taking. The comparison of 1-D activity profile for experimental data and MC simulation were always in good agreement showing that, the treatment quality assessment in proton therapy can be based on ${ \beta }+$ activity measurements.

In a carbon ion treatment the nuclear fragmentationof both target and beam projectiles impacts on the dose releasedon the tumor and on the surrounding healthy tissues. Carbon ionfragmentation occurring inside the patient body has to be stud-ied in order to take into account this contribution. These dataare also important for the development of the range monitoringtechniques with charged particles. The production of chargedfragments generated by carbon ion beams of 115-353 MeV/ukinetic energy impinging on carbon, oxygen, and hydrogen tar-gets has been measured at the CNAO particle therapy center(Pavia, Italy). The use of thin targets of graphite (C), PMMA(C2O5H8) and polyvinyl-toluene [plastic scintillator (PS), CbHa]allowed to measure fragments production cross sections, exploit-ing a time-of-flight (ToF) technique. PS detectors have been usedto perform the ToF measurements, while LYSO crystals havebeen used for the deposited energy measurement and to performparticle identification. Cross sections have been measured at 90◦and 60◦with respect to the beam direction. The measured pro-ton, deuteron, and triton differential production cross sectionson C, O, and H, obtained exploiting the target subtraction strat-egy, are presented here as a function of the fragment kineticenergy.

Spectroscopy-based photon-counting detector systems, Medipix, have many applications in medicine. Medipix detectors benefit from providing energy information as well as high spatial resolution. In this article, a review of Medipix detector technology applied to medicine and imaging techniques are presented. The technology has been used to develop quality assurance (QA) measurement devices in radiation-based treatments. A gamma camera system for radiotherapy has been developed to measure dose delivered to prostate treatments in real-time. The advantage of a high-resolution detector has been utilized in proton and heavy ion therapy for dose QA, measuring the charge particle spectra, and beam geometry for mini-beams. Applications in medical imaging using helium ion beams have been investigated to replace CT for ion beam radiotherapy. This technique provides many advantages over conventional CT such as high-resolution imaging and spectroscopy-based information for planning in helium ion treatments. The Medipix technology has shown it can be broadly applied in radiation and particle therapy applications for accurate QA as well as proving high-resolution imaging in medicine.

Positron emission tomography (PET) is one of the most mature techniques for monitoring in ion beam therapy. PET allows to reconstruct the β + activity generated in the patient by the nuclear interaction of the ions. Taking advantage of the spatial correlation between positron emitters created along the ions path and the dose distribution, it is possible to perform a quality control of the treatment. Usually, to reconstruct the activity generated within the irradiated volume, standard 3D PET reconstruction techniques are implemented. In this work, we explore a new reconstruction method (Straight Forward Reconstruction) particularly useful for reconstructing activity distribution generated by mono-energetic pencil beams. The method was validated by measuring the produced activity distribution with the DoPET system. Irradiations performed with mono-energetic pencil beams on phantoms mimicking human tissues were used for this study. Both reconstruction methods reach an accuracy in the reconstruction of the activity distribution width of the order of 1.5 mm for 2 ⋅ 1 0 8 primaries.

This paper describes the development and characterization of a Δ E-TOF detector composed of a plastic scintillator bar coupled at both ends to silicon photomultipliers. This detector is a prototype of a larger version which will be used in the FOOT (FragmentatiOn Of Target) experiment to identify the fragments produced by ion beams accelerated onto a hydrogen-enriched target. The final Δ E-TOF detector will be composed of two layers of plastic scintillator bars with orthogonal orientation and will measure, for each crossing fragment, the energy deposited in the plastic scintillator ( Δ E), the time of flight (TOF), and the coordinates of the interaction position in the scintillator. To meet the FOOT experimental requirements, the detector should have energy resolution of a few percents and time resolution of 70 ps, and it should allow to discriminate multiple fragments belonging to the same event. To evaluate the achievable performances, the detector prototype was irradiated with protons of kinetic energy in the 70–230 MeV range and interacting at several positions along the bar. The measured energy resolution σ Δ E ∕ Δ E was 6–14%, after subtracting the fluctuations of the deposited energy. A time resolution σ between 120 and 180 ps was obtained with respect to a trigger detector. A spatial resolution σ of 1.9 cm was obtained for protons interacting at the center of the bar.

FOOT (FragmentatiOn On Target) is an applied nuclear physics experiment aimed at measuring the production cross sections of fragments for energies, beams and targets relevant in particle therapy and radioprotection in space. The Δ E-TOF detector will measure the energy deposited by the fragments in a wall of plastic scintillators and the time of flight with respect to a start detector. These two quantities allow to determine the charge Z of the fragment. In this work, we summarize the charge identification procedure of a detector prototype with two scintillator modules.

Nuclear physics processes are an important source of uncertainty in dose calculations in particle therapy and radioprotection in space. Accurate cross section measurements are a crucial ingredient in improving the understanding of these processes. The FOOT (FragmentatiOn Of Target) experiment aims at measuring the production cross sections of fragments for energies, beams and targets that are relevant in particle therapy and radioprotection in space. An experimental apparatus composed of several sub-detectors will provide the mass, charge, velocity and energy of fragments produced in nuclear interactions in a thin target. A crucial component of the FOOT apparatus will be the Δ E-TOF detector, designed to identify the charge of the fragments using plastic scintillators to measure the energy deposited and the time of flight with respect to a start counter. In this work, we present a charge reconstruction procedure of produced fragments at particle therapy energies. We validate it by measuring the charges of various fragments at an angle of 3.2°and 8.3°with respect the beam-axis, using a small-scale detector and clinical beams of carbon ions at the CNAO oncology center. Experimental results agree well with FLUKA Monte Carlo simulations.

Overweight/obesity is a physical condition that affects daily activities, including walking. The main purpose of this study was to identify if there is a relationship between body mass index (BMI) and gait characteristics in young adults. 12 normal weight (NW) and 10 overweight/obese (OW) individuals walked at a self-selected speed along a 14 m indoor path. H-Gait system, combining seven inertial sensors (fixed on pelvis and lower limbs), was used to record gait data. Walking speed, spatio-temporal parameters and joint kinematics in 3D were analyzed. Differences between NW and OW and correlations between BMI and gait parameters were evaluated. Conventional spatio-temporal parameters did not show statistical differences between the two groups or correlations with the BMI. However, significant results were pointed out for the joint kinematics. OW showed greater hip joint angles in frontal and transverse planes, with respect to NW. In the transverse plane, OW showed a greater knee opening angle and a shorter length of knee and ankle trajectories. Correlations were found between BMI and kinematic parameters in the frontal and transverse planes. Despite some phenomena such as soft tissue artifact and kinematics cross-talk, which have to be more deeply assessed, current results show a relationship between BMI and gait characteristics in young adults that should be looked at in osteoarthritis prevention.

The FOOT experiment aims at identifying the fragments produced in the human body during hadrontherapy and at measuring their cross sections. The apparatus is composed of several detectors which allow a complete reconstruction of the tracks of the fragments. In particular, the Δ E-TOF detector measures the energy released in a thin plastic scintillator and the time of flight of the fragments. In this work, we report the energy and time resolution of a Δ E-TOF detector prototype with proton and carbon irradiations, and we compare the results with a Monte Carlo simulation of the optical transport in the detector. With carbon ions, we measured time resolutions of ∼ 50 ps and energy resolutions of ∼ 6%. The Monte Carlo simulation was able to model the dependence of the number of detected photons on the proton interaction position.

In this study the possibility of retrieving composition information in proton therapy with a planar in-beam PET scanner is investigated. The analysis focuses both on spatial activity distributions and time dependence of the recorded signal. The experimental data taking was performed at the Trento Proton Therapy Center (IT) by irradiating three different phantoms. We show that different phantom compositions reflect into different activity profile shapes. We demonstrate that the analysis of the event rate can provide significant information on the phantom elemental composition, suggesting that elemental analysis could be used along with activity profile analysis to achieve a more accurate treatment monitoring.

Quality assessment of particle therapy treatments by means of PET systems has been carried out since late `90 and it is one of the most promising in-vivo non invasive monitoring techniques employed clinically. It can be performed with a diagnostic PET scanners installed outside the treatment room (off-line monitoring) or inside the treatment room (in-room monitoring). However the most efficient way is by integrating a PET scanner with the treatment delivery system (on-line monitoring) so that the biological wash out and the patient repositioning errors are minimized. In this work we present the performance of the in-beam PET scanner developed within the INSIDE project. The INSIDE PET scanner is made of two planar heads, 10 cm wide (transaxially) and 25 cm long (axially), composed of pixellated LFS crystals coupled to Hamamatsu MPPCs. Custom designed Front-End Electronics (FE) and Data AcQuisition (DAQ) systems allow an on-line reconstruction of PET images from separated in-spill and inter-spill data sets. The INSIDE PET scanner has been recently delivered at the CNAO (Pavia, Italy) hadrontherapy facility and the first experimental measurements have been carried out. Homogeneous PMMA phantoms and PMMA phantoms with small air and bone inserts were irradiated with monoenergetic clinical proton beams. The activity range was evaluated at various benchmark positions within the field of view to assess the homogeneity of response of the PET system. Repeated irradiations of PMMA phantoms with clinical spread out Bragg peak proton beams were performed to evaluate the reproducibility of the PET signal. The results found in this work show that the response of the INSIDE PET scanner is independent of the position within the radiation field. Results also show the capability of the INSIDE PET scanner to distinguish variations of the activity range due to small tissue inhomogeneities. Finally, the reproducibility of the activity range measurement was within 1 mm.

One of the most promising new radiotherapy techniques makes use of charged particles like protons and carbon ions, rather than photons. At present, there are more than 50 particle therapy centers operating worldwide, and many new centers are being constructed. Positron Emission Tomography (PET) is considered a well-established non-invasive technique to monitor range and delivered dose in patients treated with particle therapy. Nuclear interactions of the charged hadrons with the patient tissue lead to the production of β+ emitting isotopes (mainly 15 O and 11 C), that decay with a short lifetime producing a positron. The two 511 keV annihilation photons can be detected with a PET detector. In-beam PET is particularly interesting because it could allow monitoring the ions range also during dose delivery. A large area dual head PET prototype was built and tested. The system is based on an upgraded version of the previously developed DoPET prototype. Each head covers now 15×15 cm 2 and is composed by 9 (3×3) independent modules. Each module consists of a 23×23 LYSO crystal matrix (2 mm pitch) coupled to H8500 PMT and is readout by custom front-end and a FPGA based data acquisition electronics. Data taken at the CNAO treatment facility in Pavia with proton and carbon beams impinging on heterogeneous phantoms demonstrate the DoPET capability to detect the presence of a small air cavity in the phantom.

We present some results obtained with silicon and gallium arsenide pixel detectors to be applied in the field of digital mammography. Even though GaAs is suitable for medical imaging applications thanks to its atomic number, which allows a very good detection efficiency, it often contains an high concentrations of traps which decrease the charge collection efficiency (CCE). So we have analysed both electrical and spectroscopic performance of different SI GaAs diodes as a function of concentrations of dopants in the substrate, in order to find a material by which we can obtain a CCE allowing the detection of all the photons that interact in the detector. Nevertheless to be able to detect low contrast details, efficiency and CCE are not the only parameters to be optimized; also the stability of the detection system is fundamental. In the past we have worked with Si pixel detectors; even if its atomic number does not allow a good detection efficiency at standard thickness, it has a very high stability. So keeping in mind the need to increase the Silicon detection efficiency we performed simulations to study the behaviour of the electrical potential in order to find a geometry to avoid the risk of electrical breakdown.

PET imaging is a non-invasive technique for particle range verification in proton therapy. It is based on measuring the beta+ annihilations caused by nuclear interactions of the protons in the patient. In this work we present measurements for proton range verification in phantoms, performed at the CNAO particle therapy treatment center in Pavia, Italy, with our 10 x 10 cm^2 planar PET prototype DoPET. PMMA phantoms were irradiated with mono-energetic proton beams and clinical treatment plans, and PET data were acquired during and shortly after proton irradiation. We created 1-D profiles of the beta+ activity along the proton beam-axis, and evaluated the difference between the proximal rise and the distal fall-off position of the activity distribution. A good agreement with FLUKA Monte Carlo predictions was obtained. We also assessed the system response when the PMMA phantom contained an air cavity. The system was able to detect these cavities quickly after irradiation., Comment: 11 pages, 6 figures, Proceedings for International Workshop on Radiation Imaging Detectors, 2014

In this study a procedure for range verification in proton therapy by means of a planar in-beam PET system is presented. The procedure consists of two steps: the measurement of the β+-activity induced in the irradiated body by the proton beam and the comparison of these distributions with simulations. The experimental data taking was performed at the CNAO center in Pavia, Italy, irradiating plastic phantoms. For two different cases we demonstrate how a real-time feedback of the delivered treatment plan can be obtained with in-beam PET imaging.

The DoPET scanner is a compact positron emission tomography (PET) device. It has been developed for monitoring the range of charged particles during therapy with hadron beams. Previous works have focused on the development and upgrade of the device and on data analysis. In this paper, a full performance characterization of the DoPET system in terms of the energy resolution, spatial resolution, sensitivity, uniformity, and noise equivalent count rate is reported. All measurements refer to an adapted version of the National Electrical Manufacturers Association (NEMA) NU 4 - 2008 protocol, which was written originally for small animal PET systems. Since DoPET is a dual head planar system, it requires a modified characterisation procedure with respect to those described for ring geometries as in the NEMA NU 4 - 2008 protocol. The presented procedure may be of interest for any other PET system with a similar geometry as DoPET.

Ion beam irradiations can deliver conformal dose distributions minimizing damage to healthy tissues thanks to their characteristic dose profiles. Nevertheless, the location of the Bragg peak can be affected by different sources of range uncertainties: a critical issue is the treatment verification. During the treatment delivery, nuclear interactions between the ions and the irradiated tissues generate β+ emitters: the detection of this activity signal can be used to perform the treatment monitoring if an expected activity distribution is available for comparison. Monte Carlo (MC) codes are widely used in the particle therapy community to evaluate the radiation transport and interaction with matter. In this work, FLUKA MC code was used to simulate the experimental conditions of irradiations performed at the Proton Therapy Center in Trento (IT). Several mono-energetic pencil beams were delivered on phantoms mimicking human tissues. The activity signals were acquired with a PET system (DoPET) based on two planar heads, and designed to be installed along the beam line to acquire data also during the irradiation. Different acquisitions are analyzed and compared with the MC predictions, with a special focus on validating the PET detectors response for activity range verification.

Background: Wearable magneto-inertial sensors are being increasingly used to obtain human motion measurements out of the lab, although their performance in applications requiring high accuracy, such as gait analysis, are still a subject of debate. The aim of this work was to validate a gait analysis system (H-Gait) based on magneto-inertial sensors, both in normal weight (NW) and overweight/obese (OW) subjects. The validation is performed against a reference multichannel recording system (STEP32), providing direct measurements of gait timings (through foot-switches) and joint angles in the sagittal plane (through electrogoniometers). Methods: Twenty-two young male subjects were recruited for the study (12 NW, 10 OW). After positioning body-fixed sensors of both systems, each subject was asked to walk, at a self-selected speed, over a 14-m straight path for 12 trials. Gait signals were recorded, at the same time, with the two systems. Spatio-temporal parameters, ankle, knee, and hip joint kinematics were extracted analyzing an average of 89 ± 13 gait cycles from each lower limb. Intraclass correlation coefficient and Bland-Altmann plots were used to compare H-Gait and STEP32 measurements. Changes in gait parameters and joint kinematics of OW with respect NW were also evaluated. Results: The two systems were highly consistent for cadence, while a lower agreement was found for the other spatio-temporal parameters. Ankle and knee joint kinematics is overall comparable. Joint ROMs values were slightly lower for H-Gait with respect to STEP32 for the ankle (by 1.9° for NW, and 1.6° for OW) and for the knee (by 4.1° for NW, and 1.8° for OW). More evident differences were found for hip joint, with ROMs values higher for H-Gait (by 6.8° for NW, and 9.5° for OW). NW and OW showed significant differences considering STEP32 (p = 0.0004), but not H-Gait (p = 0.06). In particular, overweight/obese subjects showed a higher cadence (55.0 vs. 52.3 strides/min) and a lower hip ROM (23.0° vs. 27.3°) than normal weight subjects. Conclusions: The two systems can be considered interchangeable for what concerns joint kinematics, except for the hip, where discrepancies were evidenced. Differences between normal and overweight/obese subjects were statistically significant using STEP32. The same tendency was observed using H-Gait.

We have investigated the detection performance of GaAs detectors made with different thickness and contact geometries. A comparison is made between these detection capabilities and the imaging requirements for the following medical applications: digital mammography, digital chest radiography and nuclear medicine. Experimental results and preliminary images are presented and discussed.

We present an autoradiography tool to be used mainly for genetic studies. It performs a quantitative analysis of radioactivity and can follow a dynamic process. We designed several applications, in particular one aimed at detecting hybridization of radio-labeled DNA fragments with known DNA-probes deposited on a micro-array. The technique is based on GaAs pixel array detector and low threshold, large dynamic range and good sensitivity integrated electronics developed for medical applications, suitable to detect markers (gamma or beta) such as 14C, 35S, 33P, 32P, 125I, even at very low activities. A Monte Carlo simulation of β− detection in GaAs is presented here in order to study the spatial resolution characteristics of such a system. For several biological applications, the electronics is required to perform at high temperatures (from 37° to 68°): we present here studies of noise and minimum threshold as a function of the temperature.

A GaAs pixel detector designed for digital mammography, equipped with a 36-channel single photon counting discrete read-out electronics, was tested using a test object developed for quality control purposes in mammography. Each pixel was 200×200 μm2 large, and 200 μm deep. The choice of GaAs with respect to silicon (largely used in other applications and with a more established technique) has been made because of the much better detection efficiency at mammographic energies, combined with a very good charge collection efficiency achieved thanks to new ohmic contacts. This GaAs detector is able to perform a measurement of low-contrast details, with minimum contrast lower (nearly a factor two) than that typically achievable with standard mammographic film+screen systems in the same conditions of clinical routine. This should allow for an earlier diagnosis of breast tumour masses. Due to these encouraging results, the next step in the evolution of our imaging system based on GaAs detectors has been the development of a VLSI front-end prototype chip (MEDIPIX ) in order to cover a much larger diagnostic area. The chip reads 64×64 channels in single photon counting mode, each one 170 μm wide. Each channel contains also a test input where a signal can be simulated, injecting a known charge through a 16 f F capacitor. Fake signals have been injected via the test input measuring and equalizing minimum thresholds for all the channels. On an average, in most of the performing chips available up to now, we have found that it is possible to set a threshold as low as 1800 electrons with an RMS of 150 electrons (10 standard deviations lower than the 20 keV photon signal roughly equivalent to 4500 electrons). The detector, bump-bonded to the chip, will be tested and a ladder of detectors will be prepared to be able to scan large surface objects.

A digital autoradiography system based on double sided silicon strip detectors (1.6 × 1.6 mm2 active surface with 100 μm pitch) has been developed and successfully tested with beta-emitting tracers. It is shown here that the system is able to perform imaging of organic material with specific sensitivity as small as 0.002 nCi/mm2, and to record activity measurements with good linearity in the range 0.002–20 nCi/mm2. Autoradiographic images of clusters of mammary cells marked with ortho-(32P)phosphate, obtained with an exposure time of about 10 min are presented.

In previous studies, various semi-insulating LEC GaAs crystals were irradiated with photons in the diagnostic energy range (20–100 keV), in view of a possible application in digital radiography. Solid-state and irradiation measurements, together with Monte Carlo simulations, have indicated good candidates for this application among the crystals we have investigated. In this paper we present results concerning the detection characteristics (detection efficiency, charge-collection efficiency and energy resolution as functions of the bias voltage) of one of these materials and the images obtained by a pixel detector made on the same material and a bump-bonded electronic system.

In the past few years we have developed a technological process allowing for the fabrication of radiation detectors with integrated electronics on high-resistivity silicon substrates. We report on some recent results relevant to the process optimisation and to device/circuit characterization.

Ion beam therapy is a valuable method for the treatment of deep-seated and radio-resistant tumors thanks to the favorable depth-dose distribution characterized by the Bragg peak. Hadrontherapy facilities take advantage of the specific ion range, resulting in a highly conformal dose in the target volume, while the dose in critical organs is reduced as compared to photon therapy. The necessity to monitor the delivery precision, i.e. the ion range, is unquestionable, thus different approaches have been investigated, such as the detection of prompt photons or annihilation photons of positron emitter nuclei created during the therapeutic treatment. Based on the measurement of the induced β+ activity, our group has developed various in-beam PET prototypes: the one under test is composed by two planar detector heads, each one consisting of four modules with a total active area of 10 × 10 cm2. A single detector module is made of a LYSO crystal matrix coupled to a position sensitive photomultiplier and is read-out by dedicated frontend electronics. A preliminary data taking was performed at the Italian National Centre for Oncological Hadron Therapy (CNAO, Pavia), using proton beams in the energy range of 93–112 MeV impinging on a plastic phantom. The measured activity profiles are presented and compared with the simulated ones based on the Monte Carlo FLUKA package.

The pixel identification capability is a common problem of detector systems consisting of scintillating matrices coupled to photodetectors. In positron emission tomography (PET) systems, a better pixel identification leads directly to an improvement of the spatial resolution of the system. To gain pixel identification efficiency especially at the peripheral active area, ultra-transmitting (UT) glasses can be inserted between the crystal and PMT array in order to promote light spread and avoid overlap of responses due to the enhanced light spread. Measurements with three different UT glass thicknesses ( d = 0.7 , 1.0 and 1.35 mm) have been performed in order to study their impact on pixel identification properties compared to direct coupling.

Proton beam radiotherapy is highly effective in treating cancer thanks to its conformal dose deposition. This superior capability in dose deposition has led to a massive growth of the treated patients around the world, raising the need of treatment monitoring systems. An in-treatment PET system, DoPET, was constructed and tested at CATANA beam-line, LNS-INFN in Catania, where 62 MeV protons are used to treat ocular melanoma. The PET technique profits from the beta+ emitters generated by the proton beam in the irradiated body, mainly 15-O and 11-C. The current DoPET prototype consists of two planar 15 cm × 15 cm LYSO-based detector heads. With respect to the previous versions, the system was enlarged and the DAQ up-graded during the years so now also anthropomorphic phantoms, can be fitted within the field of view of the system. To demonstrate the capability of DoPET to detect changes in the delivered treatment plan with respect to the planned one, various treatment plans were used delivering a standard 15 Gy fraction to an anthropomorphic phantom. Data were acquired during and after the treatment delivery up to 10 minutes. When the in-treatment phase was long enough (more than 1 minute), the corresponding activated volume was visible just after the treatment delivery, even if in presence of a noisy background. The after-treatment data, acquired for about 9 minutes, were segmented finding that few minutes are enough to be able to detect changes. These experiments will be presented together with the studies performed with PMMA phantoms where the DoPET response was characterized in terms of different dose rates and in presence of range shifters: the system response is linear up to 16.9 Gy/min and has the ability to see a 1 millimeter range shifter.

Open Access.-- et al., The FIRST (Fragmentation of Ions Relevant for Space and Therapy) experiment at GSI has been designed to study carbon fragmentation, measuring 12C double differential cross sections (∂2σ/∂θ∂E) for different beam energies between 100 and 1000 MeV/u. The experimental setup integrates newly designed detectors in the, so called, Interaction Region around the graphite target. The Interaction Region upstream detectors are a 250 μm thick scintillator and a drift chamber optimized for a precise measurement of the ions interaction time and position on the target. In this article we review the design of the upstream detectors along with the preliminary results of the data taking performed on August 2011 with 400 MeV/u fully stripped carbon ion beam at GSI. Detectors performances will be reviewed and compared to those obtained during preliminary tests, performed with 500 MeV electrons (at the BTF facility in the INFN Frascati Laboratories) and 80 MeV/u protons and carbon ions (at the INFN LNS Laboratories in Catania)., This work has been supported by the European Community FP7 - Capacities, contract ENSAR nº 262010. This work was also supported by Junta de Andalucia and the Spanish Ministerio de Ciencia e Innovacion Contracts P07-FQM-02894, FIS2008-04189 and FPA2008-04972-C03.

The electrical characteristics of a LPE n-type GaAs crystal have been fully measured. The experimental results were used to build a model, including the parametrization of the electric field inside the crystal, and to study the features of such material as a detector in view of a possible application for digital radiography. The predictions of a Monte Carlo based on this model are in very good agreement with the measured performances of this crystal when used as a detector for X-rays in the diagnostic energy range.

Proton therapy can overcome the limitations of conventional radiotherapy due to the more selective energy deposition in depth and to the increased biological effectiveness. Verification of the delivered dose is desirable, but the complete stopping of the protons in patient prevents the application of electronic portal imaging methods that are used in conventional radiotherapy During proton therapy β + emitters like 11 C, 15 O, 10 C are generated in irradiated tissues by nuclear reactions. The measurement of the spatial distribution of this activity, immediately after patient irradiation, can lead to information on the effective delivered dose. First, results of a feasibility study of an in-beam PET for proton therapy are reported. The prototype is based on two planar heads with an active area of about 5×5 cm 2 . Each head is made up of a position sensitive photomultiplier coupled to a square matrix of same size of LYSO scintillating crystals (2×2×18 mm 3 pixel dimensions). Four signals from each head are acquired through a dedicated electronic board that performs signal amplification and digitization. A 3D reconstruction of the activity distribution is calculated using an expectation maximization algorithm. To characterize the PET prototype, the detection efficiency and the spatial resolution were measured using a point-like radioactive source. The validation of the prototype was performed using 62 MeV protons at the CATANA beam line of INFN LNS and PMMA phantoms. Using the full energy proton beam and various range shifters, a good correlation between the position of the activity distal edge and the thickness of the beam range shifter was found along the axial direction.

Range verification with in-beam PET techniques is a powerful tool for monitoring the correctness of dose delivery in particle therapy. Among the major limitations of in-beam PET systems are the limited detectors size due to the constrained space in which they can be placed to allow the irradiation, and the necessity of a high read-out modularization, due to high activity rates during the irradiation. In this work we present the data acquired at the CNAO (Centro Nazionale di Adroterapia Oncologica) treatment center in Pavia, Italy, with the new DoPET system, specifically designed to operate in in-beam conditions. The new prototype consists of two planar 15cm × 15cm LYSO-based detectors, read out by 9 PMT detector modules each. In particular, we test the capability of our system to determine particle range in various irradiation conditions. Several plastic phantoms were irradiated at the CNAO treatment centre with protons and carbon ions of various energies. The used dose in treatment plans is 2 Gy and the monitoring feedback is produced in a few minutes after the end of the treatment.

We are implementing an X-ray breast Computed Tomography (CT) system on the gantry of a dedicated single photon emission tomography system for breast Tc-99 imaging. For the breast CT system we investigated the relevance of the beam hardening artifact. We studied the use of a single photon counting silicon pixel detector (0.3 mm thick, 256 � 256 pixel, 55mm pitch, bump-bonded to the Medipix2 photon counting readout chip) as detector unit in our X-ray CT system. We evaluated the beam hardening ‘‘cupping’’ artifact using homogeneous PMMA slabs and phantoms up to 14 cm in diameter, used as uncompressed breast tissue phantoms, imaged with a tungsten anode tube at 80 kVp with 4.2 mm Al filtration. For beam hardening evaluation we used a bimodal energy model. The CT data show a ‘‘cupping’’ artifact going from 4% (4-cm thick material) to 18% (14-cm thick material). This huge artifacts is influenced by the low detection efficiency and the charge sharing effect of the silicon pixel detector. r 2007 Published by Elsevier B.V. PACS: 85.57.cp; 87.57.Q

The aim of this work is to evaluate the capability of a single photon counting acquisition system based on the Medipix2 read-out chip for Computed Tomography (CT) applications in Small Animal Imaging. We used a micro-focus X-ray source with a W anode. The detection system is based on the Medipix2 read-out chip, bump-bonded to a 1 mm thick silicon pixel detector. The read-out chip geometry is a matrix of 256×256 cells, 55 μm×55 μm each. This system in planar radiography shows a good detection efficiency (about 70%) at the anode voltage of 30 kV and a good spatial resolution (MTF=10% @ 16.8 lp/mm). Starting from these planar performances we have characterized the system for the tomography applications with phantoms. We will present the results obtained as a function of magnification with two different background medium compositions. The effect of the reconstruction algorithm on image quality will be also discussed.

In digital imaging the ability to detect low contrast details is an aim that must be pursued. In order to achieve this result we have developed an acquisition system based on silicon pixel detector. The detector is a matrix of 256×256 square pixels of 55 μm size. It is bump-bonded to a readout chip developed by the Medipix2 Collaboration [X. Llopart, et al., IEEE Trans. Nucl. Sci, NS-49 (5) (2002) 2279]. To see the low contrast details with this system, it is necessary to reduce inside the image the fluctuations of pixel-to-pixel counts, [1] down to statistical fluctuations. This has been achieved equalizing the phantom image with a high statistics flat field acquired in the same irradiation condition. We have studied the dependence of the image uniformity for different flat field and we have investigated the dependence of the image quality on the thickness of the phantom and on the energy window selected inside the incident spectrum.

Digital mammography is entering routine clinical use and many commercial systems are now in use in the radiological units for screening and diagnostic mammography. At the same time, the research in the digital mammography field is very active in the development of more and more performing devices. In this paper we present the performance of single photon counting pixel detectors (MedipixI) tailored for digital mammographic applications. These devices are based on semiconductor (Si and GaAs) pixel detectors of different thickness, read-out by custom designed integrated circuits. To assess the imaging capability of such systems, the images of a mammographic phantom have been acquired in standard conditions for a clinical examination. The signal-to-noise ratio (SNR) of details simulating tumor masses has been evaluated. The same phantom has been also radiographed by three different commercial digital mammographic systems in the same reference conditions and a comparison in terms of SNR has been carried out. The spatial resolution of the single photon counting systems has also been evaluated by measuring the line spread function with the edge technique and then calculating the Modulation Transfer Function (MTF). The MTFs of the single photon counting systems have been compared with the MTFs of the commercial systems.

Several INFN Sections and Departments of Physics of Italian Universities have spent many man-years in the attempt to adapt detector and read-out technologies, originally developed in the field of High Energy Physics, to the domain of biomedical apparatuses. The research covered such areas as the exploitation of crystals for the production of monochromatic X-ray beams, the development of devices for efficient X-ray detection, the design of advanced VLSI electronics, the improvement of Position Sensitive Photomultiplier Tubes and crystals for Nuclear Medicine gamma-cameras. These studies have been integrated in the Integrated Mammographic Imaging (IMI) project, funded by the Italian Government through the law 46/82 (art.10) and is carried on by five high-technology industries in Italy, namely LABEN, CAEN, AMS, GILARDONI and POL.HI.TECH. We report on the status of this technological transfer project.

The Integrated Mammographic Imaging (IMI) project aims to realize innovative instrumentations for morphological and functional mammography, in particular, one of the research topics is the design and development of a prototype of a mammographic head. Innovative industrial processes for the production of GaAs pixel detectors and for their bump-bonding to the read-out VLSI electronics have been developed by AMS. The data acquisition and processing have been developed by LABEN; the power supply and distribution system has been realized by CAEN; while the integration of the head in a standard mammograph has been carried on by the Laboratori di Ricerca Gilardoni.

A multiple-exposure technique in digital mammography has been developed to suppress the physical background in the image due to Compton scattering in the body. A pair of X-ray masks, shaped in a projective geometry and positioned upstream and downstream the patient, are coupled mechanically and moved in four steps along a square pattern in order to irradiate the full area in four consecutive short exposures. A proof-of-principle apparatus is under test with a breast phantom and a standard mammographic X-ray unit. Results are reported.

We are studying the performance of various thickness GaAs pixel detectors bump-bonded to a dedicated photon counting chip (PCC) for medical imaging applications in different energy ranges. In this work we present the experimental results obtained with a 600 μm thick pixel matrix (64×64 square pixels, 170 μm side) in the 60–140 keV energy range to evaluate the possible use of such a system in the nuclear medicine field. In particular, we have measured the spectroscopic properties of the detector (charge collection efficiency, energy resolution and detection efficiency) and evaluated the discrimination capability of the electronics. Then we have measured the imaging properties of the whole system in terms of Point Spread Function and using a home made thyroid phantom. We present also a comparison with a traditional gamma camera and an evaluation, made by both experimental measurements and software simulations, of the imaging characteristics related to the use of a collimation system.

We report the status of the art of a prototype based on a GaAs pixel detector bump-bonded to a dedicated VLSI chip to be possibly used for imaging in the nuclear medicine field. This device, with a 200 μm thick pixel matrix (64×64 square pixels, 170 μm side), has already been tested with very good results for digital mammography applications (mean energy 20 keV). For more energetic photons, as in nuclear medicine, a 600 μm thick detector has been chosen. Using radioactive sources ( 241 Am, 60 keV and 99 m Tc, 140 keV photons) we have measured the performance of our prototype in terms of charge collection and detection efficiency of the detector, discrimination capability of the electronics and imaging properties of the whole system. In particular, we have evaluated the spatial resolution properties measuring the Point Spread Function and the imaging capabilities using a home made thyroid phantom. We present also the comparison between these results and those obtained with a traditional gamma camera and the evaluation, made by both experimental measurements and software simulations, of the geometry related to the use of a collimator.

We are characterising a prototype GaAs pixel detector able to perform digital mammography which contains two features which give enhanced performance compared with standard mammographic systems: it can detect low contrast test objects, inaccessible for traditional systems and, using its higher intrinsic detection efficiency, can reduce the radiation dose to the patient. The prototype is a hybrid assembly of a GaAs detector divided into 64×64 pixels, each of which measures 170 μm on the side, which is bump-bonded to a photon counting chip, PCC, developed by the Medipix collaboration. The cells of the readout chip are identical in size to the detector pixels and work in single photon counting mode. We have studied the detection efficiency of some assemblies for different bias voltages, reaching in some cases the detector breakdown point. To test the assembly in the same clinical conditions used in a standard mammographic system we have tested the prototype with radiation produced by a standard mammographic X-ray tube operating at 28 kVp. In particular, working not too far from the detector breakdown point, we are checking its imaging capabilities using a mammographic test phantom with known composition of the materials and therefore known contrast.

Thiscollaborationhasalreadyobtainedencouragingresultsabouttheperformanceof200and600mmthicksemi-insulatingGaAsdetectors,intermsofchargecollectionefficiency(c.c.e.),detectionefficiencyandimagingcapabilities,tobeusedassinglephotoncountingdetectorswithphotonsintheradiographicenergyrange.Thepossibleuseofsuchdetectorsinnuclearmedicineimpliesdetectionofmoreenergeticphotons,uptothe140keVofthe 99m Tcsource;thusefficientdetectorsmustbethickerthanthosepreviouslystudied.Inthispaper,wepresenttheresultsoftheinvestigationofelectricalanddetectionproperties(spectra,c.c.e.,energyresolution)ofaseriesofdetectors,whosethicknessrangesfrom 200to1000mm, when irradiated with radioactive sources over the energy range used in nuclear medicine.# 2001 ElsevierScienceB.V.Allrightsreserved. 1. IntroductionIn nuclear medicine, in applications as scinti-graphy and single photon emission computedtomography(SPECT)thephotonstobedetectedare emitted by a radioisotope present into thepatient thanks to a radiopharmaceutical (radio-isotope-taggedcompound),whichcanbeinjected,ingested or breathed [1], in order to ‘‘trace’’variousfunctionsofthebody.Oneoftheprimaryadvantages associated with the use of radionu-clides is the large signal (the emitted radiation)obtainedfromtherelativelysmallmassofradio-nuclide employed for a given study. The minutemass of the radiolabeled material allows for theobservation without disturbance of the systemunder study through pharmacological or toxico-logicaleffect.Thephysicalcharacteristicsofradio-nuclides that are desirable for nuclear medicineimaginginclude:asuitablephysicalhalf-life;decayvia photon emission; associated photon energyhigh enough to penetrate the body tissue withminimal tissue attenuation and low enough toallowingforminimalthicknessofcollimatorsepta;absenceofparticulateemission.

Digital radiography is a field of great interest; a wide range of different imaging systems is now becoming available and it is very important to have powerful instruments to characterize and compare their imaging properties. We have evaluated imaging properties for several digital radiographic systems in terms of resolution and noise properties. For the resolution properties, we have used the Modulation Transfer Function (MTF) and the presampling MTF, for undersampled systems. We have characterized noise properties by Detective Quantum Efficiency, that is an absolute parameter that allows comparison between different systems.

We have tested the imaging properties of a system based on a GaAs matrix that performs the direct detection of photons in the range of radiographic interest. The detector is bump-bonded to a VLSI single photon counting electronics. The imaging properties of the system have been evaluated in terms of the presampling MTF and the DQE(ν), that allow an absolute characterization of imaging properties of digital systems. We have tested other radiographic imaging systems in standard clinical conditions, using the same functions and we have compared them with the GaAs matrix system.

We present a proposal for a PET detector with a specific design oriented to its application to in-beam treatment monitoring in hadron therapy. The design is focused to the reduction of the uncertainty on the depth of the interaction of the gamma rays in the scintillator to improve the final spatial resolution of the reconstructed images. A small detector prototype, based on two staggered scintillator matrices, was assembled and irradiated with a β + emitting radioactive source. The obtained results are presented.

An analog CMOS-Integrated Circuit has been developed as Front-End for a double-sided microstrip silicon detector. The IC processes and discriminates signals in the 5–30 keV energy range. Main features are low noise and precise timing information. Low noise is achieved by optimizing the cascoded integrator with the 8 pF detector capacitance and by using an inherently low noise 1.2 μ m CMOS technology. Timing information is provided by a double discriminator architecture. The output of the circuit is a digital pulse. The leading edge is determined by a fixed threshold discriminator, while the trailing edge is provided by a zero crossing discriminator. In this paper we first describe the architecture of the Front-End chip. We then present the performance of the chip prototype in terms of noise, minimum discrimination threshold and time resolution.

We present the first results obtained using a digital imaging system, operating at room temperature, developed for medical applications working with a standard mammogrphic beam.

Ion therapy allows the delivery of highly conformal dose taking advantage of the sharp depth-dose distribution at the Bragg-peak. However, patient positioning errors and anatomical uncertainties can cause dose distortions. To exploit the full potential of ion therapy, an accurate monitoring system of the ion range is needed. Among the proposed methods to monitor the ion range, Positron Emission Tomography (PET) has proven to be the most mature technique, allowing to reconstruct the β+ activity generated in the patient by the nuclear interaction of the ions, that can be acquired during or after the treatment. Taking advantages of the spatial correlation between positron emitters created along the ions path and the dose distribution, it is possible to reconstruct the ion range. Due to the high single rates generated during the beam extraction, the acquisition of the β+ activity is typically performed after the irradiation (cyclotron) or in between the synchrotron spills. Indeed the single photon rate can be one or more orders of magnitude higher than normal for cyclotron. Therefore, acquiring the activity during the beam irradiation requires a detector with a very short dead time. In this work, the DoPET detector, capable of sustaining the high event rate generated during the cyclotron irradiation, is presented. The capability of the system to acquire data during and after the irradiation will be demonstrated by showing the reconstructed activity for different PMMA irradiations performed using clinical dose rates and the 62 MeV proton beam at the CATANA-LNS-INFN. The reconstructed activity widths will be compared with the results obtained by simulating the proton beam interaction with the FLUKA Monte Carlo. The presented data are in good agreement with the FLUKA Monte Carlo.

We describe a VLSI-based processing system performing X - Y coincidence at a very high rate in the synchronous mode. The processor has been designed for applications in digital mammography with two-sided μ-strip silicon detectors but can be used to provide the computational section of any imaging system that needs fast coincidence. The VLSI chip has been successfully tested on a 32 + 32 channels DAQ chain.

GaAs is a semiconductor suitable for room temperature X-ray detection but hitherto has suffered from incomplete charge collection and is affected by noise. Recent GaAs detectors made with LEC material have shown improved charge collection efficiency and energy resolution. In this paper we describe the fabrication process and present the results obtained with 80 μm thick pad detectors.