Purpose:
Proton computed tomography (pCT) will enable accurate prediction of proton and ion range in a patient while providing the benefit of lower radiation exposure than in x‐ray CT. The accuracy ...of the range prediction is essential for treatment planning in proton or ion therapy and depends upon the detector used to evaluate the water‐equivalent path length (WEPL) of a proton passing through the object. A novel approach is presented for an inexpensive WEPL detector for pCT and proton radiography.
Methods:
A novel multistage detector with an aperture of 10 × 37.5 cm was designed to optimize the accuracy of the WEPL measurements while simplifying detector construction and the performance requirements of its components. The design of the five‐stage detector was optimized through simulations based on the geant4 detector simulation toolkit, and the fabricated prototype was calibrated in water‐equivalent millimeters with 200 MeV protons in the research beam line of the clinical proton synchrotron at Loma Linda University Medical Center. A special polystyrene step phantom was designed and built to speed up and simplify the calibration procedure. The calibrated five‐stage detector was tested in the 200 MeV proton beam as part of the pCT head scanner, using a water phantom and polystyrene slabs to verify the WEPL reconstruction accuracy.
Results:
The beam‐test results demonstrated excellent performance of the new detector, in good agreement with the simulation results. The WEPL measurement accuracy is about 3.0 mm per proton in the 0–260 mm WEPL range required for a pCT head scan with a 200 MeV proton beam.
Conclusions:
The new multistage design approach to WEPL measurements for proton CT and radiography has been prototyped and tested. The test results show that the design is competitive with much more expensive calorimeter and range‐counter designs.
Proton radiography has applications in patient alignment and verification procedures for proton beam radiation therapy. In this paper, we report an experiment which used 200 MeV protons to generate ...proton energy-loss and scattering radiographs of a hand phantom. The experiment used the first-generation proton computed tomography (CT) scanner prototype, which was installed on the research beam line of the clinical proton synchrotron at Loma Linda University Medical Center. It was found that while both radiographs displayed anatomical details of the hand phantom, the energy-loss radiograph had a noticeably higher resolution. Nonetheless, scattering radiography may yield more contrast between soft and bone tissue than energy-loss radiography, however, this requires further study. This study contributes to the optimization of the performance of the next-generation of clinical proton CT scanners. Furthermore, it demonstrates the potential of proton imaging (proton radiography and CT), which is now within reach of becoming available as a new, potentially low-dose medical imaging modality.
Development of a head scanner for proton CT Sadrozinski, H.F.-W.; Johnson, R.P.; Macafee, S. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
01/2013, Letnik:
699
Journal Article
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Odprti dostop
We describe a new head scanner developed for Proton Computed Tomography (pCT) in support of proton therapy treatment planning, aiming at reconstructing an accurate map of the stopping power (S.P.) in ...a phantom and, in the future, in patients. The system consists of two silicon telescopes which track the proton before and after the phantom/patient, and an energy detector which measures the residual energy or range of the proton to reconstruct the Water Equivalent Path Length (WEPL) in the phantom. Based on the experience of the existing prototype and extensive Geant4 simulations and CT reconstructions, the new pCT scanner will support clinically useful proton fluxes.
Purpose:
To evaluate the spatial resolution of proton CT using both a prototype proton CT scanner and Monte Carlo simulations.
Methods:
A custom cylindrical edge phantom containing twelve ...tissue-equivalent inserts with four different compositions at varying radial displacements from the axis of rotation was developed for measuring the modulation transfer function (MTF) of a prototype proton CT scanner. Two scans of the phantom, centered on the axis of rotation, were obtained with a 200 MeV, low-intensity proton beam: one scan with steps of 4°, and one scan with the phantom continuously rotating. In addition, Monte Carlo simulations of the phantom scan were performed using scanners idealized to various degrees. The data were reconstructed using an iterative projection method with added total variation superiorization based on individual proton histories. Edge spread functions in the radial and azimuthal directions were obtained using the oversampling technique. These were then used to obtain the modulation transfer functions. The spatial resolution was defined by the 10% value of the modulation transfer function (MTF10%) in units of line pairs per centimeter (lp/cm). Data from the simulations were used to better understand the contributions of multiple Coulomb scattering in the phantom and the scanner hardware, as well as the effect of discretization of proton location.
Results:
The radial spatial resolution of the prototype proton CT scanner depends on the total path length, W, of the proton in the phantom, whereas the azimuthal spatial resolution depends both on W and the position, u
−, at which the most-likely path uncertainty is evaluated along the path. For protons contributing to radial spatial resolution, W varies with the radial position of the edge, whereas for protons contributing to azimuthal spatial resolution, W is approximately constant. For a pixel size of 0.625 mm, the radial spatial resolution of the image reconstructed from the fully idealized simulation data ranged between 6.31 ± 0.36 lp/cm for W = 197 mm i.e., close to the center of the phantom, and 13.79 ± 0.36 lp/cm for W = 97 mm, near the periphery of the phantom. The azimuthal spatial resolution ranged from 6.99 ± 0.23 lp/cm at u
− = 75 mm (near the center) to 11.20 ± 0.26 lp/cm at u
− = 20 mm (near the periphery). Multiple Coulomb scattering limits the radial spatial resolution for path lengths greater than approximately 130 mm, and the azimuthal spatial resolution for positions of evaluation greater than approximately 40 mm for W = 199 mm. The radial spatial resolution of the image reconstructed from data from the 4° stepped experimental scan ranged from 5.11 ± 0.61 lp/cm for W = 197 mm to 8.58 ± 0.50 lp/cm for W = 97 mm. In the azimuthal direction, the spatial resolution ranged from 5.37 ± 0.40 lp/cm at u
− = 75 mm to 7.27 ± 0.39 lp/cm at u
− = 20 mm. The continuous scan achieved the same spatial resolution as that of the stepped scan.
Conclusions:
Multiple Coulomb scattering in the phantom is the limiting physical factor of the achievable spatial resolution of proton CT; additional loss of spatial resolution in the prototype system is associated with scattering in the proton tracking system and inadequacies of the proton path estimate used in the iterative reconstruction algorithm. Improvement in spatial resolution may be achievable by improving the most likely path estimate by incorporating information about high and low density materials, and by minimizing multiple Coulomb scattering in the proton tracking system.
Radiation resistant LGAD design Ferrero, M.; Arcidiacono, R.; Barozzi, M. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
03/2019, Letnik:
919
Journal Article
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In this paper, we report on the radiation resistance of 50-micron thick Low Gain Avalanche Diodes (LGAD) manufactured at the Fondazione Bruno Kessler (FBK) employing different dopings in the gain ...layer. LGADs with a gain layer made of Boron, Boron low-diffusion, Gallium, Carbonated Boron and Carbonated Gallium have been designed and successfully produced at FBK. These sensors have been exposed to neutron fluences up to ϕn∼3⋅1016n∕cm2 and to proton fluences up to ϕp∼9⋅1015p∕cm2 to test their radiation resistance. The experimental results show that Gallium-doped LGAD are more heavily affected by the initial acceptor removal mechanism than those doped with Boron, while the addition of Carbon reduces this effect both for Gallium and Boron doping. The Boron low-diffusion gain layer shows a higher radiation resistance than that of standard Boron implant, indicating a dependence of the initial acceptor removal mechanism upon the implant density.
State-of-the-art and evolution of UFSD sensors design at FBK Arcidiacono, R.; Borghi, G.; Boscardin, M. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
10/2020, Letnik:
978, Številka:
C
Journal Article
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In the past few years, there has been growing interest in the development of silicon sensors able to simultaneously measure accurately the time of passage and the position of impinging charged ...particles. In this contribution, a review of the progresses in the design of UFSD (Ultra-Fast Silicon Detectors) sensors, manufactured at the FBK (Fondazione Bruno Kessler) Foundry, aiming at tracking charged particles in 4 dimensions, is presented. The state-of-the-art UFSD sensors, with excellent timing capability, are planned to be used in both ATLAS and CMS experiments detector upgrade, in order to reduce the background due to the presence of overlapping events in the same bunch crossing.
The latest results on sensors characterization including time resolution, radiation resistance and uniformity of the response are here summarized, pointing out the interplay between the design of the gain layer and the UFSD performances. The research is now focusing on the maximization of the sensor fill factor, to be able to reduce the pixel size, exploring the implementation of shallow trenches for the pixel isolation and the development of resistive AC-coupled UFSD sensors. In conclusion, a brief review on research paths tailored for detection of low energy X-rays or for low material budget applications is given.
Operation of the preclinical head scanner for proton CT Sadrozinski, H.F.-W.; Geoghegan, T.; Harvey, E. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
09/2016, Letnik:
831
Journal Article
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We report on the operation and performance tests of a preclinical head scanner developed for proton computed tomography (pCT). After extensive preclinical testing, pCT is intended to be employed in ...support of proton therapy treatment planning and pre-treatment verification in patients undergoing particle-beam therapy. In order to assess the performance of the scanner, we have performed CT scans with 200MeV protons from both the synchrotron of the Loma Linda University Medical Center (LLUMC) and the cyclotron of the Northwestern Medicine Chicago Proton Center (NMCPC). The very high sustained rate of data acquisition, exceeding one million protons per second, allowed a full 360° scan to be completed in less than 7min. The reconstruction of various phantoms verified accurate reconstruction of the proton relative stopping power (RSP) and the spatial resolution in a variety of materials. The dose for an image with better than 1% uncertainty in the RSP is found to be close to 1mGy.
LGAD designs for Future Particle Trackers Cartiglia, N.; Arcidiacono, R.; Borghi, G. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
11/2020, Letnik:
979, Številka:
C
Journal Article
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Several future high-energy physics facilities are currently being planned. The proposed projects include high energy e+e− circular and linear colliders, hadron colliders, and muon colliders, while ...the Electron–Ion Collider (EIC) is expected to construct at the Brookhaven National Laboratory in the future. Each proposal has its advantages and disadvantages in terms of readiness, cost, schedule, and physics reach, and each proposal requires the design and production of specific new detectors. This paper first presents the performances necessary for future silicon tracking systems at the various new facilities. Then it illustrates a few possibilities for the realization of such silicon trackers. The challenges posed by the future facilities require a new family of silicon detectors, where features such as impact ionization, radiation damage saturation, charge sharing, and analog read-out are exploited to meet these new demands.
Purpose:
The authors present a calibration method for a prototype proton computed tomography (pCT) scanner. The accuracy of these measurements depends upon careful calibration of the energy detector ...used to measure the residual energy of the protons that passed through the object.
Methods:
A prototype pCT scanner with a cesium iodide (CsI(Tl)) crystal calorimeter was calibrated by measuring the calorimeter response for protons of 200 and 100 MeV initial energies undergoing degradation in polystyrene plates of known thickness and relative stopping power (RSP) with respect to water. Calibration curves for the two proton energies were obtained by fitting a second-degree polynomial to the water-equivalent path length versus calorimeter response data. Using the 100 MeV calibration curve, the RSP values for a variety of tissue-equivalent materials were measured and compared to values obtained from a standard depth-dose range shift measurement using a water-tank. A cylindrical water phantom was scanned with 200 MeV protons and its RSP distribution was reconstructed using the 200 MeV calibration.
Results:
It is shown that this calibration method produces measured RSP values of various tissue-equivalent materials that agree to within 0.5% of values obtained using an established water-tank method. The mean RSP value of the water phantom reconstruction was found to be 0.995 ± 0.006.
Conclusions:
The method presented provides a simple and reliable procedure for calibration of a pCT scanner.
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