Evaluation of resistive-plate-chamber-based TOF-PET applied to in-beam particle therapy monitoring

Particle therapy is a highly conformal radiotherapy technique which reduces the dose deposited to the surrounding normal tissues. In order to fully exploit its advantages, treatment monitoring is necessary to minimize uncertainties related to the dose delivery. Up to now, the only clinically feasible technique for the monitoring of therapeutic irradiation with particle beams is Positron Emission Tomography (PET). In this work we have compared a Resistive Plate Chamber (RPC)-based PET scanner with a scintillation-crystal-based PET scanner for this application. In general, the main advantages of the RPC-PET system are its excellent timing resolution, low cost, and the possibility of building large area systems. We simulated a partial-ring scannerbeam monitoring, which has an intrinsically low positron yield compared to diagnostic PET. In addition, for in-beam PET there is a further data loss due to the partial ring configuration. In order to improve the performance of the RPC-based scanner, an improved version of the RPC detector (modifying the thickness of the gas and glass layers), providing a larger sensitivity, has been simulated and compared with an axially extended version of the crystal-based device. The improved version of the RPC shows better performance than the prototype, but the extended version of the crystal-based PET outperforms all other options. based on an RPC prototype under construction within the Fondazione per Adroterapia Oncologica (TERA). For comparison with the crystal-based PET scanner we have chosen the geometry of a commercially available PET scanner, the Philips Gemini TF. The coincidence time resolution used in the simulations takes into account the current achievable values as well as expected improvements of both technologies. Several scenarios (including patient data) have been simulated to evaluate the performance of different scanners. Initial results have shown that the low sensitivity of the RPC hampers its application to hadro

Estimating accidental coincidences for pixelated PET detectors and singles list-mode acquisition

4 pages, 1 figure.-- PACS nrs.: 87.57.Fg; 87.64.Aa; 87.53.Wz.-- ISI Article Identifier: 000244599100069Online version available 10 November 2006.We have studied the validity of random estimation techniques for various low energy thresholds (LETs) and single list-mode data sets in small animal PET. While a LET below 255 keV helps to increase the sensitivity, it also results in an increase of random coincidences and inter-crystal scatter (ICS). The study is carried out for MADPET-II, a dual-layer positron emission tomography (PET) scanner prototype consisting of LSO crystals read out individually by APDs. The data are acquired in singles list-mode format, and coincidences are computed post-acquisition. To estimate randoms, we have used the delayed coincidence window method (DW), and the singles rate model (SR). Various phantoms were simulated using GATE. For LETs under 255 keV, the number of random events R, estimated using the SR and the DW methods, is larger than the number of randoms which was directly computed from GATE simulations, and R(SR) > R(DW) > R(GATE). The higher the LET, the smaller the overestimation. For LETs > 255 keV, R(DW)/R(GATE) approximate to 1. If scattered singles were excluded from the file, this discrepancy between R(DW or SR) and R(GATE) significantly diminished. This fact points out to ICS as the effect responsible for the mismatch, since for LETs lower than 255 keV, all singles related to an ICS event can be detected independently, thus altering the singles rate. Therefore, if low LETs are used, random estimation techniques should account for ICS. (c) 2006 Elsevier B.V. All rights reserved.This work was supported in part by the Deutsche Forschungsgemeinschaft (DFG Zi615/1-2). Additional support came from the Travel Grants Acciones Integradas (Spanish Ministry of Eduaction and Science and the German DAAD, HA2004-0082) and Marina Bueno (CSIC, Spain, B2004DE01).Peer reviewe

Coincidence Tests of a Compton Telescope Based on Continuous LaBr3 Crystals and SiPMs for Dose Monitoring in Hadron Therapy

International audienceIn hadron therapy, a proton or carbon ion beam interacts with the tissue and prompt gamma rays are emitted from the excited nuclei that can be employed for dose monitoring. A Compton telescope makes it possible to locate the origin of these photons, allowing an indirect estimation of the delivered dose. The telescope prototype being developed at IFIC-Valencia within the ENVISION project will consist of three detector layers. Each layer will be composed of a continuous LaBr3 crystal coupled to four Silicon Photomultiplier (SiPM) arrays. Coincidence tests have been carried out with a first layer of a 16 mm × 18 mm × 5 mm LaBr3 crystal coupled to a 16 mm × 18 mm SiPM array and a second layer of a 12 mm × 12 mm × 5 mm LYSO crystal coupled to another 16 mm × 18 mm SiPM array. The test system is read out by two SPIROC1 boards working in time coincidence. First data have been taken and the results demonstrate the feasibility of operating the system

Noise evaluation of Compton camera imaging for proton therapy

Compton Cameras emerged as an alternative for real-time dose monitoring techniques for Particle Therapy (PT), based on the detection of prompt-gammas. As a consequence of the Compton scattering process, the gamma origin point can be restricted onto the surface of a cone (Compton cone). Through image reconstruction techniques, the distribution of the gamma emitters can be estimated, using cone-surfaces backprojections of the Compton cones through the image space, along with more sophisticated statistical methods to improve the image quality. To calculate the Compton cone required for image reconstruction, either two interactions, the last being photoelectric absorption, or three scatter interactions are needed. Because of the high energy of the photons in PT the first option might not be adequate, as the photon is not absorbed in general. However, the second option is less efficient. That is the reason to resort to spectral reconstructions, where the incoming γ energy is considered as a variable in the reconstruction inverse problem. Jointly with prompt gamma, secondary neutrons and scattered photons, not strongly correlated with the dose map, can also reach the imaging detector and produce false events. These events deteriorate the image quality. Also, high intensity beams can produce particle accumulation in the camera, which lead to an increase of random coincidences, meaning events which gather measurements from different incoming particles. The noise scenario is expected to be different if double or triple events are used, and consequently, the reconstructed images can be affected differently by spurious data. The aim of the present work is to study the effect of false events in the reconstructed image, evaluating their impact in the determination of the beam particle ranges. A simulation study that includes misidentified events (neutrons and random coincidences) in the final image of a Compton Telescope for PT monitoring is presented. The complete chain of detection, from the beam particle entering a phantom to the event classification, is simulated using FLUKA. The range determination is later estimated from the reconstructed image obtained from a two and three-event algorithm based on Maximum Likelihood Expectation Maximization. The neutron background and random coincidences due to a therapeutic-like time structure are analyzed for mono-energetic proton beams. The time structure of the beam is included in the simulations, which will affect the rate of particles entering the detector

Test of a Compton Telescope Prototype Based on Continuous LaBr3 Crystals and Silicon Photomultipliers

International audienceA Compton telescope prototype for dose monitoring in hadron therapy has been developed. The camera is based on continuous LaBr3 and LYSO crystals coupled to silicon photomultipliers for detection and readout respectively. The setup consists of a 16x18x5 mm3 LaBr3 crystal coupled to a 16x18 mm2 MPPC array as a first layer of the telescope, and a 12x12x5 mm3 LYSO crystal coupled to another 16x182 mm MPPC array as a second layer. The SPIROC1 ASIC is employed as readout electronics. The first coincidence tests have been successfully carried out and allow the reconstruction of a point-like source, in different positions, encouraging the development and the improvement of the prototype to a full imaging system

За кадры. 1998. № 10 (2989)

"Время не властно над ними, они снова на передовой" / А. В. ВодопьяновА завтра грянет первомай... / Н. Глушко"Памяти павших будьте достойны..." / Н. ГлушкоМемориал на Смоленщине / И. Т. ЛозовскийМастер / В. Г. Лукьянов, В. Ф. Куцепаленко140 лет со дня рождения профессора В. П. Алексеевского / Ю. М. ЛозинскийУ вас есть шанс! / Ю. ГренкинДан приказ ему на запад, ей - в другую сторону... / В. СложноцветныхНазад, в прошлое... / А. НемыкинПисьмо в редакцию / Н. Хлебникова [и др.

Medical Imaging

F. Azaiez et al.; Chapter II; 28 figs.; 5 tabs.Peer Reviewe