The dose accumulation and the impact of deformable image registration on dose reporting parameters in a moving patient undergoing proton radiotherapy

INTRODUCTION: Potential changes in patient anatomy during proton radiotherapy may lead to a deviation of the delivered dose. A dose estimate can be computed through a deformable image registration (DIR) driven dose accumulation. The present study evaluates the accumulated dose uncertainties in a patient subject to an inadvertent breathing associated motion. MATERIALS AND METHODS: A virtual lung tumour was inserted into a pair of single participant landmark annotated computed tomography images depicting opposite breathing phases, with the deep inspiration breath-hold the planning reference and the exhale the off-reference geometry. A novel Monte Carlo N-Particle, Version 6 (MCNP6) dose engine was developed, validated and used in treatment plan optimization. Three DIR methods were compared and used to transfer the exhale simulated dose to the reference geometry. Dose conformity and homogeneity measures from International Committee on Radioactivity Units and Measurements (ICRU) reports 78 and 83 were evaluated on simulated dose distributions registered with different DIR algorithms. RESULTS: The MCNP6 dose engine handled patient-like geometries in reasonable dose calculation times. All registration methods were able to align image associated landmarks to distances, comparable to voxel sizes. A moderate deterioration of ICRU measures was encountered in comparing doses in on and off-reference anatomy. There were statistically significant DIR driven differences in ICRU measures, particularly a 10% difference in the relative D(98%) for planning tumour volume and in the 3 mm/3% gamma passing rate. CONCLUSIONS: T he dose accumulation over two anatomies resulted in a DIR driven uncertainty, important in reporting the associated ICRU measures for quality assurance

Depth Profile Analysis of Deep Level Defects in 4H- SiC Introduced by Radiation

Deep level defects created by implantation of light-helium and medium heavy carbon ions in the single ion regime and neutron irradiation in n- type 4H-SiC are characterized by the DLTS technique. Two deep levels with energies 0.4 eV (EH1) and 0.7 eV (EH3) below the conduction band minimum are created in either ion implanted and neutron irradiated material beside carbon vacancies (Z1/2). In our study, we analyze components of EH1 and EH3 deep levels based on their concentration depth profiles, in addition to (−3/=) and (=/−) transition levels of silicon vacancy. A higher EH3 deep level concentration compared to the EH1 deep level concentration and a slight shift of the EH3 concentration depth profile to larger depths indicate that an additional deep level contributes to the DLTS signal of the EH3 deep level, most probably the defect complex involving interstitials. We report on the introduction of metastable M-center by light/medium heavy ion implantation and neutron irradiation, previously reported in cases of proton and electron irradiation. Contribution of M-center to the EH1 concentration profile is presented

Reliability of haemophilia early arthropathy detection with ultrasound (HEAD-US) in children

BACKGROUND: Ultrasound (US) has been proven to be reliable in the assessment of early haemophilic arthropathy in the adult haemophilic population, however few studies so far focused on the reliability of US specifically in the paediatric haemophilic population. We were interested if the changing appearance of the growing bone hinders the ultrasonographic evaluation of the pathologic processes caused by haemophilic arthropathy. The aim of the study was to assess the reliability of US for evaluation of haemophilic arthropathy in children in comparison to magnetic resonance imaging (MRI). PATIENTS AND METHODS: The study included all children aged 6 years or more with severe haemophilia in the country (n = 10). We assessed their elbows, knees, and ankles bilaterally by US and compared the results to the MRI as the reference standard. Pearson correlation coefficient (r) was used to analyse correlation. RESULTS: The correlation with MRI for the US for the total score was excellent for all joints (r = 0.849 for the elbows, r = 1 for knees, r = 0.842 for ankles). The correlation of scores for specific joint components showed fair, moderate, or excellent correlation for all joint components in all joints. The correlation was the lowest for the evaluation of cartilage and bone in the ankles (r = 0.546 and r = 0.478) and bone in the elbows (r = 0.499). CONCLUSIONS: Our study proved that US using the HEAD-US method performed by paediatric radiologists is a reliable tool for detection and quantification of haemophilic arthropathy in children in comparison to MRI

M-Center in Neutron-Irradiated 4H-SiC

We report on the metastable defects introduced in the n-type 4H-SiC material by epithermal and fast neutron irradiation. The epithermal and fast neutron irradiation defects in 4H-SiC are much less explored compared to electron or proton irradiation-induced defects. In addition to the carbon vacancy (Vc), silicon vacancy (Vsi) and carbon antisite-carbon vacancy (CAV) complex, the neutron irradiation has introduced four deep-level defects, all arising from the metastable defect, the M-center. The metastable deep-level defects were investigated by deep level transient spectroscopy (DLTS), high-resolution Laplace DLTS (L-DLTS) and isothermal DLTS. The existence of the fourth deep-level defect, M4, recently observed in ion-implanted 4H-SiC, has been additionally confirmed in neutron-irradiated samples. The isothermal DLTS technique has been proven as a useful tool for studying the metastable defect

4H-SiC Schottky barrier diodes for efficient thermal neutron detection

In this work, we present the improved efficiency of 4H-SiC Schottky barrier diodes-based detectors equipped with the thermal neutron converters. This is achieved by optimizing the thermal neutron converter thicknesses. Simulations of the optimal thickness of thermal neutron converters have been performed using two Monte Carlo codes (Monte Carlo N–Particle Transport Code and Stopping and Range of Ions in Matter). We have used 6LiF and 10B4C for the thermal neutron converter material. We have achieved the thermal neutron efficiency of 4.67% and 2.24 % with 6LiF and 10B4C thermal neutron converters, respectively

Nuclear Cogeneration of Methanol and Acetaldehyde from Ethylene Glycol Using Ionizing Radiation

Despite offering low-carbon and reliable energy, the utilization of nuclear energy is declining globally due to high upfront capital costs and longer returns on investments. Nuclear cogeneration of valuable chemicals from waste biomass-derived feedstocks could have beneficial impacts while harnessing the underutilized resource of ionizing energy. Here, we demonstrate selective methanol or acetaldehyde production from ethylene glycol, a feedstock derived from glycerol, a byproduct of biodiesel, using irradiations from a nuclear fission reactor. The influence of radiation quality, dose rate, and the absorbed dose of irradiations on radiochemical yields (G-value) has been studied. Under low-dose-rate, γ-only radiolysis during reactor shutdown rate (<0.018 kGy min–1), acetaldehyde is produced at a maximum G-value of 8.28 ± 1.05 μmol J–1 and a mass productivity of 0.73 ± 0.06% from the 20 kGy irradiation of neat ethylene glycol. When exposed to a high-dose-rate (6.5 kGy min–1), 100 kGy mixed-field of neutron + γ-ray radiations, the radiolytic selectivity is adjusted from acetaldehyde to generate methanol at a G-value of 2.91 ± 0.78 μmol J–1 and a mass productivity of 0.93 ± 0.23%. Notably, utilizing 422 theoretical systems could contribute to 4.96% of worldwide acetaldehyde production using a spent fuel pool γ-ray scheme. This research reports G-values and production capacities for acetaldehyde for high-dose scenarios and shows the potential selectivity of a nuclear cogeneration process to synthesize chemicals based on their irradiation conditions from the same reagent

HTR-PROTEUS Pebble Bed Experimental Program Cores 1, 1A, 2, and 3: Hexagonal Close Packing with a 1:2 Moderator-to-Fuel Pebble Ratio

In its deployment as a pebble bed reactor (PBR) critical facility from 1992 to 1996, the PROTEUS facility was designated as HTR-PROTEUS. This experimental program was performed as part of an International Atomic Energy Agency (IAEA) Coordinated Research Project (CRP) on the Validation of Safety Related Physics Calculations for Low Enriched HTGRs. Within this project, critical experiments were conducted for graphite moderated LEU systems to determine core reactivity, flux and power profiles, reaction-rate ratios, the worth of control rods, both in-core and reflector based, the worth of burnable poisons, kinetic parameters, and the effects of moisture ingress on these parameters. Four benchmark experiments were evaluated in this report: Cores 1, 1A, 2, and 3. These core configurations represent the hexagonal close packing (HCP) configurations of the HTR-PROTEUS experiment with a moderator-to-fuel pebble ratio of 1:2. Core 1 represents the only configuration utilizing ZEBRA control rods. Cores 1A, 2, and 3 use withdrawable, hollow, stainless steel control rods. Cores 1 and 1A are similar except for the use of different control rods; Core 1A also has one less layer of pebbles (21 layers instead of 22). Core 2 retains the first 16 layers of pebbles from Cores 1 and 1A and has 16 layers of moderator pebbles stacked above the fueled layers. Core 3 retains the first 17 layers of pebbles but has polyethylene rods inserted between pebbles to simulate water ingress. The additional partial pebble layer (layer 18) for Core 3 was not included as it was used for core operations and not the reported critical configuration. Cores 1, 1A, 2, and 3 were determined to be acceptable benchmark experiments