We investigate, by means of Geant4 simulations, a real-time method to control the position of the Bragg peak during ion therapy, based on a Compton camera in combination with a beam tagging device ...(hodoscope) in order to detect the prompt gamma emitted during nuclear fragmentation. The proposed set-up consists of a stack of 2
mm thick silicon strip detectors and a LYSO absorber detector. The
γ
emission points are reconstructed analytically by intersecting the ion trajectories given by the beam hodoscope and the Compton cones given by the camera. The camera response to a polychromatic point source in air is analyzed with regard to both spatial resolution and detection efficiency. Various geometrical configurations of the camera have been tested. In the proposed configuration, for a typical polychromatic photon point source, the spatial resolution of the camera is about 8.3
mm FWHM and the detection efficiency 2.5×10
−4 (reconstructable photons/emitted photons in
4
π
). Finally, the clinical applicability of our system is considered and possible starting points for further developments of a prototype are discussed.
The advantage of using reinforcing substrate layers with phosphor screens is that they increase the phosphor sensitivity and filter the scattered radiation, while providing a mechanical support for ...the phosphor layer. A simulation model based on the Monte Carlo code Geant4 was developed to study the influence of the substrate properties (material, thickness) on the phosphor screen spatial response. The optimal substrate/phosphor combinations have been determined at given sensitivity of the screen. Of all studied cases at medium energy (300 keV), a configuration with slight improvement in the screen spatial response has been found. Moreover, the results show that, without degrading the performances of the screen, the phosphor thickness may be significantly reduced (by 35% in the case of a 0.05 mm Pb substrate). Besides, PolyEthylene Terephthalate (PET) makes a good mechanical support (of up to minimum 4 mm in thickness) for the phosphor layer. The simulation methodology permitted to study the role played by the X-ray and electron processes inside the substrate layer.
With the development of fast sampling electronics, digital pulse processing techniques for PET signals are raising interest. The optimal filter (OF) algorithm reconstructs pulse amplitude and time by ...two weighted sums, making it compatible with real-time implementation. The filters are usually optimized for stationary noise. We developed and tested a method to optimize the filters for the nonstationary noise of scintillation pulses. It is based on offline statistical analysis of coincident waveforms that could be applied during the system initialization phase. Experimental tests were done on a coincidence setup with two detection blocks composed of a fast inorganic scintillator ( LaBr 3 or LYSO) coupled to a photodetector (APD or PMT), preamplifiers and prefilters. The signals were sampled at high rate (250 MHz for APDs, 5 GHz for PMTs) and treated offline. The optimization of the filter coefficients for nonstationary noise yielded a significant improvement compared to those optimized for stationary noise, resp. 368 ps and 632 ps fwhm in coincidence for the LYSO-PMT setup. However, little improvement was achieved compared to leading-edge (DLED) and constant fraction (DCFD) discriminator algorithms (resp. 419 ps, 435 ps fwhm). Indeed, the adjustment of thresholds can be interpreted as an optimization for nonstationary noise. Yet, OF is more robust to white noise than DLED or DCFD. The applicability to PET is discussed.
We present the first results obtained with a detector, called Large Area Pixelized Detector (LAPD), dedicated to the study the ballistic control of the beam delivered to the patient by in-beam and ...real time detection of secondary particles, emitted during its irradiation in the context of hadrontherapy. These particles are 511keV γ from the annihilation of a positron issued from the β+ emitters induced in the patient tissues along the beam path. The LAPD basic concepts are similar to a conventional PET camera. The 511keV γ are detected and the reconstructed lines of response allow to measure the β+ activity distribution. Nevertheless, when trying to use γ from positron annihilation for the ballistic control in hadrontherapy, the large prompt γ background should be taken into account and properly rejected. First reconstruction results, obtained with a phantom filled with a high intensity FDG source at the cancer research centre of Clermont-Ferrand are shown. We also report results of measurements performed at the Heidelberg Ion-Beam Therapy Centre with one third of the detector, using proton and carbon ion beams.
Ion-induced cell killing has been reported to depend on the irradiation dose but also on the projectile parameters. In this paper we focus on two approaches developed and extensively used to predict ...cell survival in response to ion irradiation: the Local Effect Model and the Katz Model. These models are based on a track-structure description summarized in the concept of radial dose. This latter is sensitive to ion characteristics parameters and gives to both models the ability to predict some important radiobiological features for ion irradiations. Radial dose is however an average quantity, which does not include stochastic effects. These radiation-intrinsic effects are investigated by means of a Monte Carlo simulation of dose deposition. We show that both models are not fully consistent with the nanometric and microscopic dose deposition statistics.
Testbeam studies of production modules of the ATLAS Tile Calorimeter Alexa, C.; Anderson, K.; Biscarat, C. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
07/2009, Letnik:
606, Številka:
3
Journal Article
Recenzirano
Odprti dostop
We report test beam studies of 11% of the production ATLAS Tile Calorimeter modules. The modules were equipped with production front-end electronics and all the calibration systems planned for the ...final detector. The studies used muon, electron and hadron beams ranging in energy from 3 to 350GeV.
Two independent studies showed that the light yield of the calorimeter was ∼70pe/GeV, exceeding the design goal by 40%. Electron beams provided a calibration of the modules at the electromagnetic energy scale. Over 200 calorimeter cells the variation of the response was 2.4%. The linearity with energy was also measured. Muon beams provided an intercalibration of the response of all calorimeter cells. The response to muons entering in the ATLAS projective geometry showed an RMS variation of 2.5% for 91 measurements over a range of rapidities and modules. The mean response to hadrons of fixed energy had an RMS variation of 1.4% for the modules and projective angles studied. The response to hadrons normalized to incident beam energy showed an 8% increase between 10 and 350GeV, fully consistent with expectations for a noncompensating calorimeter. The measured energy resolution for hadrons of σ/E=52.9%/E⊕5.7% was also consistent with expectations.
Other auxiliary studies were made of saturation recovery of the readout system, the time resolution of the calorimeter and the performance of the trigger signals from the calorimeter.
A collimated gamma camera coupled to a beam hodoscope is currently under development within the CLaRyS collaboration to provide ion-range verification during hadrontherapy. We propose a µTCA-based ...data acquisition (DAQ) system that consists of dedicated front-end boards, a multi-optical DAQ board, a reference clock board and a computer. Several specific developments have been performed in the front-end boards, namely a TDC (time-to-digital converter) based system synchronization, and an adjustable-depth data buffer, a histogram-based fast time-of-flight estimation and an easy adaptation for different applications. All these DAQ developments have been recently tested with reduced-size hodoscope and collimated camera in the Mediterranean Protontherapy Institute in Nice (65 MeV proton beam).
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