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Application of TG-100 risk analysis methods to the acceptance testing and commissioning process of a Halcyon linear accelerator
摘要： Purpose: A new type of linear accelerator (linac) was recently introduced into the market by a major manufacturer. Our institution is one of the early users of this pre-assembled and pre-configured dual-layer MLC, ring-gantry linac – HalcyonTM (1st version). We performed a set of full acceptance testing and commissioning (ATC) measurements for three Halcyon machines and compared the measured data with the standard beam model provided by the manufacturer. The ATC measurements were performed following the guidelines given in different AAPM protocols as well as guidelines provided by the manufacturer. The purpose of the present work was to perform a risk assessment of the ATC process for this new type of linac and investigate whether the results obtained from this analysis could potentially be used as a guideline for improving the design features of this type of linac. Methods: AAPM’s TG100 risk assessment methodology was applied to the ATC process. The acceptance testing process relied heavily on the use of a manufacturer-supplied phantom and the automated analysis of EPID images. For the commissioning process, a conventional measurement setup and process (e.g. use of water tank for scanning) was largely used. ATC was performed using guidelines recommended in various AAPM protocols (e.g. TG-106, TG-51) as well as guidelines provided by the manufacturer. Six medical physicists were involved in this study. Process maps, process steps and failure modes (FMs) were generated for the ATC procedures. Failure Modes and Effects Analysis (FMEA) were performed following the guidelines given in AAPM TG-100 protocol. The top 5 and top 10 highest-ranked FMs were identified for the acceptance and commissioning procedures respectively. Quality control measures were suggested to mitigate these FMs. Results: A total of 38 steps and 88 FMs were identified for the entire ATC process. 14 steps and 34 FMs arose from acceptance testing. The top 5 FMs that were identified could potentially be mitigated by the manufacturer. For commissioning, a total of 24 steps and 54 potential FMs were identified. The use of separate measurement tools that are not machine-integrated has been identified as a cause for the higher number of steps and FMs generated from the conventional ATC approach. More than half of the quality control measures recommended for both acceptance and commissioning could potentially be incorporated by the manufacturer in the design of the Halcyon machine. Conclusion: This paper presents the results of Failure Modes and Effects Analysis and quality control measures to mitigate the failure modes for the acceptance testing and commissioning process for Halcyon machine. Unique FMs that result from the differences in the ATC guidelines provided by the vendor and current conventional protocols, and the challenges of performing the ATC due to the new linac features and ring-gantry design were highlighted for the first time. The FMs identified in the present work along with the suggested quality control measures, could potentially be used to improve the design features of future ring-gantry type of linacs that are likely to be pre-assembled, pre-configured, and heavily reliant on automation and image-guidance.
关键词： new ring-gantry linac,reference dosimetry,TG100,TG-51,Failure Modes and Effects Analysis (FMEA),Acceptance testing and Commissioning
更新于2025-09-23 15:23:52
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Measurement of bunch length evolution in electron beam macropulse of S-band linac using coherent edge radiation
摘要： Intense coherent edge radiation (CER) with a power of 0.10 mW was observed in a straight line with an undulator of Kyoto University Free Electron Laser (KU-FEL). To investigate the evolution of a bunch length in a macropulse of an electron beam, a technique was developed using the CER beam. The measured air-extracted CER beam pro?le has a hollow structure resembling the ?rst-order Laguerre–Gaussian mode with asymmetric intensity in horizontal direction. It roughly agrees with the pro?le calculated considering the effective area of a de?ection mirror employed to extract the beam from the FEL optical cavity into air. The root-mean-squared (RMS) bunch length determined from a measured spectrum of the CER beam is 60 μm for an electron-beam macropulse. Changes in the CER intensity in the electron-beam macropulse were measured by diode detectors with short time constants at two frequencies. The evolution of the RMS bunch length was determined using the ratio of the CER intensity at the two frequencies. It could be concluded that the evolution correlated with the macropulse structure of the FEL power. Therefore, measuring the evolution of the CER intensity at multiple frequencies proved useful to control FEL macropulses.
关键词： Bunch length,Terahertz,Coherent edge radiation,Free-electron laser,Linac
更新于2025-09-23 15:23:52
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G4Linac_MT, an easy-to-use Geant4-based code for modeling medical linear accelerator
摘要： In this paper, we present G4Linac_MT, a simple-to-use open source code developed to facilitate the use of the Geant4 C++ toolkit for the simulation of a medical linear accelerator (linac). This multithreaded code encapsulates several well-developed C++ modules serving to handle the complexity of coding geometry and material, to easy plot histograms of various physics quantities, to auto-merge output data created by all working threads into a single file, to well-estimate the number of simulated primary particles required to achieve data with a statistical uncertainty < 1% and also the CPU time required for, to use a set of variance reduction techniques as bremsstrahlung splitting, particle recycling, particle rotational splitting and stacking mechanism, to use a new format of phase space file based on HDF5-C++ scientific library which has been developed specially for this code. In order to minimize human effort required by Geant4 coding and validating of a linac, the code comes with a Java-based GUI application which contains separated GUI modules for linac head simulation, dose calculation, data analysis, geometry modeling and gamma index calculation. Results from Monte Carlo simulations of linac head of a Saturne 43 12 MV configuring a 10 × 10 cm2 radiation field are showed in order to demonstrate the G4Linac_MT capabilities. Thus, comparisons between simulated dosimetric functions and measured ones in a water phantom have been established by using a gamma index method and the results show a good agreement within 2.6%-1 mm accuracy. In addition, after optimizing variance reduction techniques, the overall CPU time spent by this multithreaded code has been decreased by a factor of 7.
关键词： Multi-threading,G4Linac_MT,Monte Carlo,Geant4,Linac
更新于2025-09-23 15:22:29
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Technical Note: <scp>EPID</scp> 's response to 6? <scp>MV</scp> photons in a strong, parallel magnetic field
摘要： Purpose: Electronic portal imaging devices (EPIDs) are potentially useful for dosimetric verification in integrated MRI-linac systems. This work presents the reproducibility, linearity, image lag, and radiation field profiles in a conventional EPID, with and without a 0.5 T parallel magnetic field present in a 6 MV photon beam. Methods: An aS500 EPID was modified to function in strong magnetic fields. All measurements were made using the linac-MR installed at the Cross Cancer Institute. The EPID remained stationary on the couch between the measurements made with and without magnetic field. We measured short-term reproducibility of dark and flood fields, signal linearity from 1 to 500 MU irradiations, and image lag post 100 MU irradiation. An ion chamber was used to measure any linac output variations to correct the EPID signal due to these variations for the duration of experiment. X-axis and Y-axis radiation field profiles were obtained from the EPID image resulting from a 10 9 10 cm2 radiation field delivery. Results: The average pixel value ((cid:1)standard deviation) of flood field with and without magnetic fields were 57,876 (cid:1) 379 and 57,703 (cid:1) 366, respectively, and the corresponding average dark field pixel values were (cid:3)32.05 (cid:1) 0.85 and (cid:3)32.19 (cid:1) 0.97. The maximum difference in image linearity data with and without magnetic field is 0.2% which is well within the measurement uncertainty of 0.65%. Similarly, the image lag curves, with and without the magnetic field, were nearly identical. The first measured point, with mean lag signal of 1.44% without and 1.41% with magnetic field, shows that the largest difference is well below the uncertainty in the EPID signal measurement. The radiation field profiles obtained with and without magnetic fields were nearly identical; 91.3% of the X-axis and 95.2% of the Y-axis profile points pass a gamma criterion of 1% and 1 mm. Conclusions: A conventional EPID imager with a 0.1 cm copper plate responds to 6 MV photons similarly irrespective of the strong magnetic field being off or on in the parallel orientation to the radiation beam. Thus, the EPID is a potentially useful tool for pretreatment dosimetric verification in linac-MR systems using parallel magnetic field.
关键词： linac-MR,MRI-linac,EPID
更新于2025-09-23 15:19:57
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Empirical Law to Evaluate the Skin Dose with Photon Beam Energy and Irradiation Field Size
摘要： The objective of this study is to evaluate mathematically an empirical law governs the skin dose with photon beam energy and irradiation field size based on experiment data of dose distributions. The dose distributions were expressed on percentage depth dose (PDD). The measurements of PDDs were done as a function of irradiation field size with an uncertainty of 2% as recommended by IAEA protocols. The skin dose corresponds to PDD at depth of 0 mm for photon beam energy of 6 and 18 MV. For these both photon beam energies, the skin dose increased linearly with irradiation field size and the skin dose rate decreased in power law as a function of irradiation field size with mathematical error under to 10%. This law allows us to predict the skin dose with irradiation field size for high radiotherapy quality and high protection of organ at risks.
关键词： skin dose,linac,dosimetry,radiotherapy,PDD
更新于2025-09-19 17:15:36
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Design of Energy Recovery Linac for a Source of High-Flux Gamma-ray by Laser Compton Scattering
摘要： We investigate the generations of a high-?ux γ-ray beams by laser Compton scattering. We performed the design of an energy recovery linac that produces a γ-ray beam with the ?ux of ～ 1013 photons/s. It is important to examine the e?ects on beam performances of the ERL in detail. Thus, we examined the e?ects of emittance growths on higher order modes in the superconducting linac and coherent synchrotron radiation in the designed lattice of the energy recovey linac. They were checked by performing the start-to-end simulation of multi-beam particle trackings in the designed 355 MeV ERL. It was shown that the energy recovery linacs by laser Compton scattering may provide monochromatic high-?ux gamma-ray beams. It is shown through our design studies that goals of γ-ray beam parameters in the ERL facility are achievable. Such an energy-tunable γ-ray beams that are generated by laser Compton scattering may be applied to nuclear resonance ?uorescence(NRF) measurements for the non-destructive detection of radioactive nuclear materials. The investigations show that our design studies provide a good optimized ERL parameters in terms of beam dynamics.
关键词： Supercavity,High-?ux gamma rays,Laser Compton scattering,Nuclear resonance ?uorescence,Energy recovery linac
更新于2025-09-12 10:27:22
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Microbunch Rotation and Coherent Undulator Radiation from a Kicked Electron Beam
摘要： Coherent emission from a microbunched electron beam is the driving force behind the revolution in light sources, enabling x-ray free-electron lasers (FELs) to emit pulses 9 orders of magnitude brighter than previous sources. Microbunches form perpendicular to the electron travel direction, and the conventional understanding is that they shear rather than rotate in response to a transverse kick, locking FEL facilities into a single-user operating mode. In this paper, we show that microbunches rotate toward the new direction of travel if the electron beam is kicked and defocused. We provide evidence that microbunch rotation explains the unexpectedly large amount of off-axis radiation observed during experiments at the Linac Coherent Light Source. We demonstrate that LCLS can be multiplexed into at least three separate beams using this principle. Finally, we propose using a magnetic triplet to rotate microbunches through significantly larger angles without microbunch degradation. This new understanding of microbunch dynamics can lead to significantly improved multiplexing at FEL facilities, microbunch preservation through a bend, and x-ray pulses with a pulse-front tilt.
关键词： electron beam,Linac Coherent Light Source,coherent undulator radiation,x-ray free-electron lasers,microbunch rotation
更新于2025-09-09 09:28:46
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[IEEE 2018 IEEE International Symposium on Technologies for Homeland Security (HST) - Woburn, MA, USA (2018.10.23-2018.10.24)] 2018 IEEE International Symposium on Technologies for Homeland Security (HST) - Development of Dual Energy Container Inspection System for Harbor Security in KAERI
摘要： The use of multiple energy X-rays can provide additional information as compared to a single energy X-ray for the security inspection of cargo such as containers. Using the 9/6 MeV dual energy X-ray and material discrimination algorithms, it is possible to distinguish between low-density (organic) and high-density (inorganic) materials through the intended color mapping. The material discrimination algorithm can obtain the material information of the image used for screening by exploiting the characteristic that the energy-dependent attenuation coefficient is different even though the same material is used. Based on these technologies, we have developed a security inspection system for container cargo that consists of a radiation source, a detector array, four- collimators, a moving stage, and an imaging system. The radiation source was developed based on a dual-energy radio- frequency (RF) electron linear-accelerator (LINAC) with a spot size of 0.9 mm, and a 5.5 MW S-band magnetron was used as a RF generator. The detector is composed of 43 modules in one array and 32 channels per module, and the moving stage is designed and manufactured to transport cargo of up to 70 tons in the horizontal direction of the radiation beam at an optimized speed of 300 mm per second. The imaging system controls the whole process of the security inspection system from the operation of equipment to the acquisition and discrimination of images. In this paper, we introduce the characteristics of the developed inspection system and explain the results obtained by ANSI N42.46, the international recommendation scanner performance test.
关键词： Material decomposition,Dual-energy LINAC,Cargo Security Inspection System
更新于2025-09-04 15:30:14
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[IEEE 2017 IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC) - Atlanta, GA, USA (2017.10.21-2017.10.28)] 2017 IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC) - Design of a Photoneutron Convertor for Energy Selective Neutron Imaging
摘要： Neutron imaging plays an essential role in the industrial applications, such as turbine blade manufacturing, fuel cell research, and nuclear fuel quality inspection. As isotopic neutron sources and neutron generators cannot provide high-intensity neutron beams, and neutron beam lines of research reactors or spallation neutron sources are very scarce, a cost-effective neutron source with high neutron yield and long life-span should be researched. The e-LINAC driven photoneutron source, which converts X-rays to photoneutrons, has been proved to be a robust neutron source that can realize neutron yield ranging from 1010 to 1015n/s. Hence it is a promising neutron source to provide neutron beams used for the neutron imaging. Because the e-LINAC works at a pulsed mode and the photoneutrons have a continuous energy spectrum, energy selective neutron imaging can thus be realized with the e-LINAC driven photoneutron source, with the aid of time of flight (TOF) technique. In this research, an e-LINAC driven photoneutron source is researched to strike the compromise between the neutron flux and the energy resolution. With a well-designed heavy water photon-to-neutron convertor, a 10 MeV/ 20 kW e-LINAC can provide a thermal neutron flux of 7.28×104n/cm2/s at 10 meters away from the electron target, with an energy resolution less than 20%. By using a low temperature (10K) moderator, the cold neutron flux at the same position can be 2.13×104n/cm2, and the energy resolution is less than 2%. This study may help realize the energy selective neutron imaging with an e-LINAC driven photoneutron source.
关键词： Neutron imaging,e-LINAC,energy selective neutron imaging,photoneutron source,time of flight (TOF)
更新于2025-09-04 15:30:14