A Monte-Carlo-based study of a single-2D-detector proton-radiography system

PURPOSE: To assess the feasibility of a proton radiography (pRG) system based on a single thin pixelated detector for water-equivalent path length (WEPL) and relative stopping power (RSP) measurements.METHODS: A model of a pRG system consisting of a single pixelated detector measuring energy deposition and proton fluence was investigated in a Geant4-based Monte Carlo study. At the position directly after an object traversed by a broad proton beam, spatial 2D distributions are calculated of the energy deposition in, and the number of protons entering the detector. Their ratio relates to the 2D distribution of the average stopping power of protons in the detector. The system response is calibrated against the residual range in water of the protons to provide the 2D distribution of the WEPL of the object. The WEPL distribution is converted into the distribution of the RSP of the object. Simulations have been done, where the system has been tested on 13 samples of homogeneous materials of which the RSPs have been calculated and compared with RSPs determined from simulations of residual-range-in-water, which we refer to as reference RSPs.RESULTS: For both human-tissue- and non-human-tissue-equivalent materials, the RSPs derived with the detector agree with the reference values within 1%.CONCLUSION: The study shows that a pRG system based on one thin pixelated detection screen has the potential to provide RSP predictions with an accuracy of 1%.</p

A simple microscopy setup for visualizing cellular responses to DNA damage at particle accelerator facilities

Cellular responses to DNA double-strand breaks (DSBs) not only promote genomic integrity in healthy tissues, but also largely determine the efficacy of many DNA-damaging cancer treatments, including X-ray and particle therapies. A growing body of evidence suggests that activation of the mechanisms that detect, signal and repair DSBs may depend on the complexity of the initiating DNA lesions. Studies focusing on this, as well as on many other radiobiological questions, require reliable methods to induce DSBs of varying complexity, and to visualize the ensuing cellular responses. Accelerated particles of different energies and masses are exceptionally well suited for this task, due to the nature of their physical interactions with the intracellular environment, but visualizing cellular responses to particle-induced damage - especially in their early stages - at particle accelerator facilities, remains challenging. Here we describe a straightforward approach for real-time imaging of early response to particle-induced DNA damage. We rely on a transportable setup with an inverted fluorescence confocal microscope, tilted at a small angle relative to the particle beam, such that cells can be irradiated and imaged without any microscope or beamline modifications. Using this setup, we image and analyze the accumulation of fluorescently-tagged MDC1, RNF168 and 53BP1—key factors involved in DSB signalling—at DNA lesions induced by 254 MeV α-particles. Our results provide a demonstration of technical feasibility and reveal asynchronous initiation of accumulation of these proteins at different individual DSBs

Quantitative Comparison of Commercial and Non-Commercial Metal Artifact Reduction Techniques in Computed Tomography

Objectives Typical streak artifacts known as metal artifacts occur in the presence of strongly attenuating materials in computed tomography (CT). Recently, vendors have started offering metal artifact reduction (MAR) techniques. In addition, a MAR technique called the metal deletion technique (MDT) is freely available and able to reduce metal artifacts using reconstructed images. Although a comparison of the MDT to other MAR techniques exists, a comparison of commercially available MAR techniques is lacking. The aim of this study was therefore to quantify the difference in effectiveness of the currently available MAR techniques of different scanners and the MDT technique. Materials and Methods Three vendors were asked to use their preferential CT scanner for applying their MAR techniques. The scans were performed on a Philips Brilliance ICT 256 (S1), a GE Discovery CT 750 HD (S2) and a Siemens Somatom Definition AS Open (S3). The scans were made using an anthropomorphic head and neck phantom (Kyoto Kagaku, Japan). Three amalgam dental implants were constructed and inserted between the phantom's teeth. The average absolute error (AAE) was calculated for all reconstructions in the proximity of the amalgam implants. Results The commercial techniques reduced the AAE by 22.0 +/- 1.6%, 16.2 +/- 2.6% and 3.3 +/- 0.7% for S1 to S3 respectively. After applying the MDT to uncorrected scans of each scanner the AAE was reduced by 26.1 +/- 2.3%, 27.9 +/- 1.0% and 28.8 +/- 0.5% respectively. The difference in efficiency between the commercial techniques and the MDT was statistically significant for S2 (p = 0.004) and S3 (p <0.001), but not for S1 (p = 0.63). Conclusions The effectiveness of MAR differs between vendors. S1 performed slightly better than S2 and both performed better than S3. Furthermore, for our phantom and outcome measure the MDT was more effective than the commercial MAR technique on all scanners

Data from: Quantitative comparison of commercial and non-commercial metal artifact reduction techniques in computed tomography

Objectives: Typical streak artifacts known as metal artifacts occur in the presence of strongly attenuating materials in computed tomography (CT). Recently, vendors have started offering metal artifact reduction (MAR) techniques. In addition, a MAR technique called the metal deletion technique (MDT) is freely available and able to reduce metal artifacts using reconstructed images. Although a comparison of the MDT to other MAR techniques exists, a comparison of commercially available MAR techniques is lacking. The aim of this study was therefore to quantify the difference in effectiveness of the currently available MAR techniques of different scanners and the MDT technique. Materials and Methods: Three vendors were asked to use their preferential CT scanner for applying their MAR techniques. The scans were performed on a Philips Brilliance ICT 256 (S1), a GE Discovery CT 750 HD (S2) and a Siemens Somatom Definition AS Open (S3). The scans were made using an anthropomorphic head and neck phantom (Kyoto Kagaku, Japan). Three amalgam dental implants were constructed and inserted between the phantom’s teeth. The average absolute error (AAE) was calculated for all reconstructions in the proximity of the amalgam implants. Results: The commercial techniques reduced the AAE by 22.0±1.6%, 16.2±2.6% and 3.3±0.7% for S1 to S3 respectively. After applying the MDT to uncorrected scans of each scanner the AAE was reduced by 26.1±2.3%, 27.9±1.0% and 28.8±0.5% respectively. The difference in efficiency between the commercial techniques and the MDT was statistically significant for S2 (p=0.004) and S3 (p<0.001), but not for S1 (p=0.63). Conclusions: The effectiveness of MAR differs between vendors. S1 performed slightly better than S2 and both performed better than S3. Furthermore, for our phantom and outcome measure the MDT was more effective than the commercial MAR technique on all scanners

The production of positron emitters with millisecond half-life during helium beam radiotherapy

Therapy with helium ions is currently receiving significantly increasing interest because helium ions have a sharper penumbra than protons and undergo less fragmentation than carbon ions and thus require less complicated dose calculations. For any ion of interest in hadron therapy, the accuracy of dose delivery is limited by range uncertainties. This has led to efforts by several groups to develop in vivo verification techniques, including positron emission tomography (PET), for monitoring of the dose delivery. Beam-on PET monitoring during proton therapy through the detection of short-lived positron emitters such as N-12 (T-1/2 = 11 ms), an emerging PET technique, provides an attractive option given the achievable range accuracy, minimal susceptibility to biological washout and provision of near prompt feedback. Extension of this approach to helium ions requires information on the production yield of relevant short-lived positron emitters. This study presents the first measurements of the production of short-lived positron emitters in water, graphite, calcium and phosphorus targets irradiated with 59 MeV/u He-3 and 50 MeV/u He-4 beams. For these targets, the most produced short-lived nuclides are O-13/N-12 (T-1/2 = 8.6/11 ms) on water, O-13/N-12 on graphite, Ti-43/Sc-41/Sc-42 (T-1/2 = 509-680 ms) on calcium, P-28 (T-1/2 = 268 ms) on phosphorus. A translation of the results from elemental targets to PMMA and representative tissues such as adipose tissue, muscle, compact and cortical bone, shows the dominance of O-13/N-12 in at least the first 20 s of an irradiation with He-4 and somewhat longer with He-3. As the production of O-13/N-12 in a He-3 irradiation is 3-4 times higher than in a He-4 irradiation, from a statistical point of view, range verification using O-13/N-12 PET imaging will be about 2 times more precise for a He-3 irradiation compared to a He-4 irradiation

The increase in average absolute error (AAE) of all standard CT reconstructions of the phantom containing three amalgam implants as a function of the position of the slice.

<p>A high error was observed in a 9 mm wide region around the amalgam implants at 0 mm. In addition, a high error was observed at -48 mm and +24 mm which were caused by movement of the tongue and the upperjaw due to the insertion of amalgam implants respectively. S1: Philips Brilliance ICT 256, S2: GE Discovery CT 750 HD, S3: Siemens Somatom Definition AS Open.</p

Scan protocol for the CT scans of the three scanners.

<p>S1: Philips Brilliance ICT 256, S2: GE Discovery CT 750 HD, S3: Siemens Somatom Definition AS Open, O-MAR: Metal Artifact Reduction for Orthopedic Implants, SMAR: Smart Metal Artifact Reduction, MARIS: Metal Artifact Reduction in Image Space.</p><p>* S2 scanned using dual energy. S3 used both a metal artifact reduction technique based on single and on dual energy using a tube voltage of 140/80 kV.</p><p>Scan protocol for the CT scans of the three scanners.</p

The average absolute error (AAE) with and without different metal artifact reduction (MAR) techniques.

<p>(a) The AAE between reference scans, for scans without MAR, for scans with the commercial MAR technique and for scans corrected using the MDT software. For S3, MAR2 is displayed. (b) The AAE reduction after the application of both the commercial MAR techniques and the metal deletion technique (MDT). S1: Philips Brilliance ICT 256, S2: GE Discovery CT 750 HD, S3: Siemens Somatom Definition AS Open.</p

The Kyoto Kagaku PH-47 head/neck phantom.

<p>(a) The assembled phantom. (b) The disassembled jaw.</p

Relative electron density determination using a physics based parameterization of photon interactions in medical DECT

Radiotherapy and particle therapy treatment planning require accurate knowledge of the electron density and elemental composition of the tissues in the beam path to predict the local dose deposition. We describe a method for the analysis of dual energy computed tomography (DECT) images that provides the electron densities and effective atomic numbers of tissues. The CT measurement process is modelled by system weighting functions, which apply an energy dependent weighting to the parameterization of the total cross section for photon interactions with matter. This detailed parameterization is based on the theoretical analysis of Jackson and Hawkes and deviates, at most, 0.3% from the tabulated NIST values for the elements H to Zn. To account for beam hardening in the object as present in the CT image we implemented an iterative process employing a local weighting function, derived from the method proposed by Heismann and Balda. With this method effective atomic numbers between 1 and 30 can be determined. The method has been experimentally validated on a commercially available tissue characterization phantom with 16 inserts made of tissue substitutes and aluminium that has been scanned on a dual source CT system with tube potentials of 100 kV and 140 kV using a clinical scan protocol. Relative electron densities of all tissue substitutes have been determined with accuracy better than 1%. The presented DECT analysis method thus provides high accuracy electron densities and effective atomic numbers for radiotherapy and especially particle therapy treatment planning