Search

Hadron therapy is a radiotherapy modality which offers a precise energy deposition to the tumors and a dose reduction to healthy tissue as compared to conventional methods. However, methods for real-time monitoring are required to ensure that the radiation dose is deposited on the target. The IRIS group of IFIC-Valencia developed a Compton camera prototype for this purpose, intending to image the Prompt Gammas emitted by the tissue during irradiation. The system detectors are composed of Lanthanum (III) bromide scintillator crystals coupled to silicon photomultipliers. After an initial characterization in the laboratory, in order to assess the system capabilities for future experiments in proton therapy centers, different tests were carried out in two facilities: PARTREC (Groningen, The Netherlands) and the CNA cyclotron (Sevilla, Spain). Characterization studies performed at PARTREC indicated that the detectors linearity was improved with respect to the previous version and an energy resolution of 5.2 % FWHM at 511 keV was achieved. Moreover, the imaging capabilities of the system were evaluated with a line source of 68Ge and a point-like source of 241Am-9Be. Images at 4.439 MeV were obtained from irradiation of a graphite target with an 18 MeV proton beam at CNA, to perform a study of the system potential to detect shifts at different intensities. In this sense, the system was able to distinguish 1 mm variations in the target position at different beam current intensities for measurement times of 1800 and 600 s.

The use of Compton cameras for medical imaging and its interest as a hadron therapy treatment monitoring has increased in the last decade with the development of silicon photomultipliers. MACACO is a Compton camera prototype designed and assembled at the IRIS group of IFIC-Valencia. This Compton camera is based on monolithic Lanthanum (III) Bromide crystals and silicon photomultipliers, and employs the novel TOFPET2 ASIC as readout electronics. This system emerged as an alternative to MACACO II prototype, with the aim of improving its limited time resolution. To test the performance of the ASIC in a Compton camera setup, the prototype was characterized, both in laboratory and in-beam. A time resolution of 1.5 ns was obtained after time corrections, which improves greatly the performance of the MACACO II. Moreover, the results obtained at high photon energies demonstrate the ability of the system to obtain 1 mm displacements of the reconstructed spots. The results reinforce the potential of the system as a monitoring device for hadron therapy.

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 um) have been chosen as possible candidates. The 25 up photodetector provided better performance in therms 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 1mm displacements in the target position.

The applicability extent of hadron therapy for tumor treatment is currently limited by the lack of reliable online monitoring techniques. An active topic of investigation is the research of monitoring systems based on the detection of secondary radiation produced during treatment. MACACO, a multi-layer Compton camera based on LaBr scintillator crystals and SiPMs, is being developed at IFIC-Valencia for this purpose. This work reports the results obtained from measurements of a 150 MeV proton beam impinging on a PMMA target. A neural network trained on Monte Carlo simulations is used for event selection, increasing the signal to background ratio before image reconstruction. Images of the measured prompt gamma distributions are reconstructed by means of a spectral reconstruction code, through which the 4.439 MeV spectral line is resolved. Images of the emission distribution at this energy are reconstructed, allowing calculation of the distal fall-off and identification of target displacements of 3 mm.

The IRIS group at IFIC-Valencia has developed a second version of a Compton camera prototype for hadron therapy treatment monitoring, with the aim of improving the performance with respect to its predecessor. The system is composed of three Lanthanum (III) bromide (LaBr) crystals coupled to silicon photomultipliers (SiPMs). The detector energy resolution has been improved to 5.6% FWHM at 511 keV and an angular resolution of 8.0° has been obtained. Images of a Na point-like source have been reconstructed selecting two and three interaction events. Moreover, the experimental data have been reproduced with Monte Carlo simulations using a Compton camera module (CCMod) in GATE v8.2 obtaining a good correlation.

La terapia hadrónica es una técnica de tratamiento del cáncer consistente en la irradiación de tumores con protones u otros iones ligeros. El uso de esta técnica se ha incrementado por su ventaja de maximización de la dosis depositada sobre un tumor y de reducción de toxicidad del tratamiento comparado con la radioterapia convencional. Sin embargo, una de sus desventajas es la dificultad en la monitorización del rango del haz. Las cámaras Compton han resurgido como posibles candidatas para la monitorización de la terapia hadrónica, mediante la detección de los fotones producidos en la desexcitación de núcleos de los tejidos irradiados.El grupo IRIS del IFIC en Valencia se encuentra desarrollando un prototipo de una cámara Compton con la finalidad de ser empleada en monitorización de la terapia hadrónica. El prototipo MACACO (Medical Applications CompAct COmpton camera) se compone de cristales centelleadores de LaBr3 acoplados a una matriz de fotomultiplicadores de silicio. Con la finalidad de mejorar las prestaciones del prototipo, se ha construido una tercera versión que presenta un rendimiento mejorado respecto de sus predecesores. Los nuevos detectores de MACACO III se componen de cristales continuos de LaBr3 de 25,8 x 25,8 mm2 y 5 mm. El sistema de lectura AliVATA, desarrollado por el grupo, opera el ASIC VATA64HDR16 utilizado como electrónica de lectura. La caracterización de los detectores en el laboratorio se ha realizado utilizando fuentes radiactivas de 22Na, 152Eu y 137Cs. El mejor valor de resolución energética obtenido ha sido de 4.8 % FWHM a 662 keV, resolución angular de 6.0° FWHM a 1275 keV y eficiencia de detección en coincidencias de 1 x 10−3 a 1275 keV. A partir de los datos experimentales se han reconstruido imágenes de una fuente puntual de 22Na seleccionando eventos dobles y triples. El código de reconstrucción de MACACO III produce imágenes cuatridimensionales (energía y posición) usando eventos dobles o triples. Imágenes con la combinación de

One factor limiting the current applicability extent of hadron therapy is the lack of a reliable method for real time treatment monitoring. The use of Compton imaging systems as monitors requires the correct reconstruction of the distribution of prompt gamma productions during patient irradiation. In order to extract the maximum information from all the measurable events, we implemented a spectral reconstruction method that assigns to all events a probability of being either partial or total energy depositions. The method, implemented in a list-mode maximum likelihood expectation maximization algorithm, generates a four dimensional image in the joint spatial-spectral domain, in which the voxels containing the emission positions and energies are obtained. The analytical model used for the system response function is also employed to derive an analytical expression for the sensitivity, which is calculated via Monte Carlo integration. The performance of the method is evaluated through reconstruction of various experimental and simulated sources with different spatial and energy distributions. The results show that the proposed method can recover the spectral and spatial information simultaneously, but only under the assumption of ideal measurements. The analysis of the Monte Carlo simulations has led to the identification of two important degradation sources: the mispositioning of the gamma interaction point and the missing energy recorded in the interaction. Both factors are related to the high energy transferred to the recoil electrons, which can travel far from the interaction point and even escape the detector. These effects prevent the direct application of the current method in more realistic scenarios. Nevertheless, experimental point-like sources have been accurately reconstructed and the spatial distributions and spectral emission of complex simulated phantoms can be identified.

Purpose Real-time monitoring is still a challenge in hadrontherapy. With this aim, a Compton telescope prototype (MACACO) has been developed by the IRIS group at IFIC-Valencia within the European project ENVISION. The second prototype MACACO II is an upgrade developed with the purpose of enhancing its performance. Material and Methods MACACO II consists of three layers of LaBr3 monolithic crystals coupled to silicon photomultiplier (SiPM) arrays. New crystals have been coupled to 8x8 pixel SiPM arrays from Hamamatsu Photonics (S13361-3050AE-08). Moreover, an improved image reconstruction code including an accurate model for the sensitivity matrix has been implemented. The telescope has been characterized in the laboratory with 22Na and 152Eu sources and tested in two accelerator centres. The first test took place at CNA (Sevilla) with a 18 MeV proton beam impinging on a graphite target in order to produce 4.4 MeV gamma rays. A second test was held in KVI-CART (Groningen) with a 150 MeV proton beam hitting a PMMA target. Monte Carlo simulations have been carried out with GATE V 7.0. Results In the laboratory, the energy resolution has been improved and an angular resolution of 4.6° has been achieved, which together with the improved reconstruction code, have led to a better image quality. The efficiency measured with two planes in coincidence at 1275 keV is 1.0x10-3. Monte Carlo simulations result in a good correlation with the experimental parameters. Regarding the In-beam experiments, two target positions separated by 5 mm have been reconstructed from the CNA test-beam. Furthermore, KVI-CART test-beam results show that Bragg distribution correlates to the PMMA position. Conclusions MACACO II has shown a better performance than the previous prototype. The testbeam results have demonstrated the ability to reconstruct different positions. Further improvements are ongoing in order to achieve the required performance for the application.

Hadron therapy (HT) is a technique used in cancer treatment that consists in the irradiation of tumours using light ions or protons instead of photons. HT treatment monitoring in real-time is one of the main challenges addressed nowadays. The IRIS group (http://ific.uv.es/iris) at IFIC-Valencia is developing a Compton telescope with this purpose. The system is made of three LaBr3 detector planes coupled to silicon photomultipliers (SiPMs). A first prototype (MACACO: Medical Applications CompAct COmpton camera) was successfully developed, with promising results. A second version has been developed with the aim of improving the system performance, including new detectors for the first two planes and an improved image reconstruction code, improving significantly the performance tests in laboratory and accelerator facilities. The performance improvement of MACACO II was verified through experimental tests. In addition, Monte Carlo simulations were made with GATE v 7.0 getting a good correlation with the experimental measurements. In this poster we present results corresponding to the two-layer layout with the new detectors.

The IRIS group at IFIC Valencia is developing a three-layer Compton camera for treatment monitoring in ion beam therapy. The system is composed of three detector planes, each made of a LaBr 3 monolithic crystal coupled to SiPM arrays. The first prototype (MACACO), was fully characterised in the laboratory and in beam tests demonstrating the feasibility of the proposed technology. A second prototype (MACACO II), described in this work, is currently being developed to improve performance. The SiPM arrays have been replaced by newer models, leading to an improved detector energy resolution which translates into a higher spatial resolution of the telescope. In addition, the image reconstruction code has been improved with an accurate model of the sensitivity matrix. Furthermore, a new spectral reconstruction algorithm for Compton cameras with two planes has been developed showing promising results. The system has been fully characterised in the laboratory at controlled temperature and also tested in two accelerator facilities. The first involved a proton beam of 18 MeV impinging a graphite target. The results allowed the successful reconstruction of two target positions separated by 5 mm. The second test beam used protons of 150 MeV impinging on a PMMA target. The results show that for measurements taken in different positions of the PMMA target the reconstructed Bragg peak position is related to the PMMA position.

The use of hadron therapy in cancer treatment is increasing in the world given its precise energy deposition to the tumour and the dose reduction to healthy tissue as compared to conventional photon radiotherapy. Realtime treatment monitoring is one of the main challenges addressed nowadays. The IRIS group at IFIC-Valencia is developing a Compton telescope with this purpose. The system is made of three LaBr3 detector planes coupled to silicon photomultipliers (SiPMs). The first MACACO (Medical Applications CompAct COmpton camera) prototype demonstrated the viability of the proposed technology and served to identify its limitations. The second prototype features new detectors and image reconstruction codes, improving significantly the performance [1,2]. MACACO II has been characterized in the laboratory and in beam tests. It has been tested at CNA (Sevilla) with 18 MeV proton beams on a graphite target to produce 4.4 MeV gamma rays. Data have been taken with the system in different positions and beam intensities, and the target image has been reconstructed. Further tests have been carried out at KVI-CART (Groningen) with a 150 MeV proton beam impinging a PMMA target and the Bragg peak has been reconstructed in different positions. In spite of the significant progress, the system does not yet reach the necessary performance for the application and thus, possible improvements are being assessed. Tests include the evaluation of SiPMs of different types and manufacturers to enhance energy resolution and the improvement of the readout electronics. The MADDAQ board currently employed is being replaced by AliVATA, that will allow to operate the three system detectors with just one board and improve the readout speed. In addition, tests are being carried out with the PETsys system, improving significantly the detector timing resolution.

The IRIS group at IFIC Valencia is developing a three-layer Compton camera for treatment monitoring in ion beam therapy. The system is composed of three detector planes, each made of a LaBr3 monolithic crystal coupled to SiPM arrays. The first prototype (MACACO) was fully characterised in the laboratory and in beam tests demonstrating the feasibility of the proposed technology. A second prototype (MACACO II), described in this work, is currently being developed to improve performance. The SiPM arrays have been replaced by newer models, leading to an improved detector energy resolution which translates into a higher spatial resolution of the telescope. A new coincidence board allows acquisition of data with any two or all three detectors simultaneously. In addition, the image reconstruction code has been improved with an accurate model of the sensitivity matrix. The device has also been tested in two accelerator facilities. The first involved a proton beam of 18 MeV impinging a graphite target. The results allowed the successful reconstruction of two target positions separated by 5 mm. The second test beam used protons of 150 MeV impinging on a PMMA target. Preliminary analysis results show prompt-gamma energy spectra as expected for these proton energies. Analysis of this data is ongoing, with the aim of reconstructing the Bragg peak profilein the PMMA target. Further improvements to the readout electronics are also underway.