Bragg Peak Shift Research Articles

Transient heating of Pd nanoparticles studied by x-ray diffraction with time of arrival photon detection.

Pulsed laser heating of an ensemble of Pd nanoparticles, supported by a MgO substrate, is studied by x-ray diffraction. By time-resolved Bragg peak shift measurements due to thermal lattice expansion, the transient temperature of the Pd nanoparticles is determined, which quickly rises by at least 100 K upon laser excitation and then decays within 90 ns. The diffraction experiments were carried out using a Cu x-ray tube, giving continuous radiation, and the hybrid pixel detector Timepix3 operating with single photon counting in a time-of-arrival mode. This type of detection scheme does not require time-consuming scanning of the pump-probe delay. The experimental time resolution is estimated at 15 ± 5 ns, which is very close to the detector's limit and matches with the 7 ns laser pulse duration. Compared to bulk metal single crystals, it is discussed that the maximum temperature reached by the Pd nanoparticles is higher and their cooling rate is lower. These effects are explained by the oxide support having a lower heat conductivity.

A Conformable Holographic Sensing Bandage for Wound Monitoring

AbstractChronic wound monitoring can provide personalized pathophysiological information for wound management and treatment. Continuously monitoring the wound milieu via the holographic pH sensor can reflect the wound healing processes. However, the integration with wearable devices is hindered by its inherently restricted interrogation angle dependency within 5°. Herein, a ball bearing‐based double photopolymerization method is developed to fabricate holographic pH sensors with a broader interrogation angle range of 15°–60° in wound exudates. The fabricated holographic pH sensor is then integrated with the flexible ultrathin polyurethane substrate, which replays a total Bragg peak shift of approximately 150 nm with physiological pH changes from 7.00 to 8.75. The conformable holographic pH sensing bandages demonstrate the ability to quantify the pH value under various bending manipulations, simulating the mounting on the body surface. The reversibility in artificial wound exudate demonstrates the durability and capability of real‐time pH monitoring in the wound milieu with minimal effect on the replay wavelength. The addition of electrolytes, albumin, urea, uric acid, lactate, and glucose does not interfere with the readout over the physiological pH range of wound exudates. The obtained conformable holographic sensing bandage benefits the wound healing process monitoring through colorimetric interrogation at point‐of‐care (POC) settings.

Dielectric properties of conventional and microwave sintered Lanthanum doped CaCu3Ti4O12 ceramics for high-frequency applications

The colossal dielectric response of La-doped CaCu3Ti4O12 ceramics has been probed at room temperature for a frequency of 1Hz–20 MHz. In this work, the La-doped (CaCu3Ti4O12)x samples for x = 0.1, 0.2, and 0.3 have been sintered at 1100 °C using two different heating modes. SEM and EDS analysis investigated the microstructural chrysalis, grain size distribution, and the inhibitions of Cu-rich phase segregation into grain boundaries by the effect of La3+. The presence of main cubic single-phase of CCTO and the diminutive Bragg peak shift due to ion size effect of La3+ and Ca2+ have been identified by XRD for both conventional (CS) and microwave sintered (MWS) samples. XPS study revealed the effect of La3+ on the binding energies of Cu and Ti in CCTO. The dielectric properties namely dielectric constant (ϵ), tan δ, and dielectric relaxation peaks were measured using BDS in which CS and MWS La-doped samples demonstrated (ϵ) ∼ >104 and ∼ >103 along with low tan δ for x ≥ 0.1 at medium and high frequency (104–107Hz) than pure CCTO.

Stopping-power ratio of mouthpiece materials for charged-particle therapy in head and neck cancer

In this study, the stopping-power ratios (SPRs) of mouthpiece materials were measured and the errors in the predicted SPRs based on conversion table values were further investigated. The SPRs of the five mouthpiece materials were predicted from their computed tomography (CT) numbers using a calibrated conversion table. Independently, the SPRs of the materials were measured from the Bragg peak shift of a carbon-ion beam passing through the materials. The errors in the SPRs of the materials were determined as the difference between the predicted and measured values. The measured SPRs (errors) of the Nipoflex 710™ and Bioplast™ ethylene–vinyl acetate copolymers (EVAs) were 0.997 (0.023) and 0.982 (0.007), respectively. The SPRs of the vinyl silicon impression material, light-curable resin, and bis-acrylic resin were 1.517 (0.134), 1.161 (0.068), and 1.26 (0.101), respectively. Among the five tested materials, the EVAs had the lowest SPR errors, indicating the highest human-tissue equivalency.

Assessment of the impact of CT calibration procedures for proton therapy planning on pediatric treatments.

Relative stopping powers (RSPs) for proton therapy are estimated using single-energy computed tomography (SECT), calibrated with standardized tissues of the adult male. It is assumed that those tissues are representative of tissues of all age and sex. Female, male, and pediatric tissues differ from one another in density and composition. In this study, we use tabulated pediatric tissues and computational phantoms to investigate the impact of this assumption on pediatric proton therapy. The potential of dual-energy CT (DECT) to improve the accuracy of these calculations is explored. We study 51 human body tissues, categorized into male/female for the age groups newborn, 1-, 5-, 10-, and 15-year-old children, and adult, with given compositions and densities. CT numbers are simulated and RSPs are estimated using SECT and DECT methods. Estimated tissue RSPs from each method are compared to theoretical RSPs. The dose and range errors of each approach are evaluated on three computational phantoms (Ewing's sarcoma, salivary sarcoma, and glioma) derived from pediatric proton therapy patients. With SECT, soft tissues have mean estimation errors and standard deviation up to (1.96±4.18)% observed in newborns, compared to (0.20±1.15)% in adult males. Mean estimation errors for bones are up to (-3.35±4.76)% in pediatrics as opposed to (0.10±0.66)% in adult males. With DECT, mean errors reduce to (0.17±0.13)% and (0.23±0.22)% in newborns (soft tissues/bones). With SECT, dose errors in a Ewing's sarcoma phantom are exceeding 5Gy (10% of prescribed dose) at the distal end of the treatment field, with volumes of dose errors >5Gy of mm3 . Similar observations are made in the head and neck phantoms, with overdoses to healthy tissue exceeding 2Gy (4%). A systematic Bragg peak shift resulting in either over- or underdosage of healthy tissues and target volumes depending on the crossed tissues RSP prediction errors is observed. Water equivalent range errors of single beams are between -1.53 and 5.50mm (min, max) (Ewing's sarcoma phantom), -0.78 and 3.62mm (salivary sarcoma phantom), and -0.43 and 1.41mm (glioma phantom). DECT can reduce dose errors to <1Gy and range errors to <1mm. Single-energy computed tomography estimates RSPs for pediatric tissues with systematic shifts. DECT improves the accuracy of RSPs and dose distributions in pediatric tissues compared to the SECT calibration curve based on adult male tissues.

Determination of atomistic deformation of tricalcium silicate paste with high‐volume fly ash

AbstractWe examined the effect of incorporating high‐volume fly ash on the atomic arrangement and interatomic deformation behavior of calcium silicate hydrates in tricalcium silicate paste upon exposure to external forces. The interatomic structural changes and strains under compressive load were assessed using synchrotron in situ high‐energy X‐ray scattering‐based atomic pair distribution function analysis. Three different types of strains, which were (a) macroscopic strains from gauges on the surfaces of specimen, (b) strains in a reciprocal space (Bragg peak shift), and (c) strains in real space (PDF peak shift), were compared to each other. All monitored and calculated strains for tricalcium silicate‐fly ash (50 wt% fly ash) paste were compared with the counterparts of the pure tricalcium silicate paste. Pair distribution function analysis in the range of r &lt; 10 Å indicated that the atomic arrangement of tricalcium silicate‐fly ash was similar to that of synthetic calcium silicate hydrates followed by that of pure tricalcium silicate paste. Moreover, the pair distribution function refinement results revealed that the calcium silicate hydrate structure in tricalcium silicate‐fly ash paste was similar to tobermorite 11 Å, unlike that in pure tricalcium silicate paste. The interatomic strain of tricalcium silicate‐fly ash in the real space (r &lt; 20 Å) was smaller than that of tricalcium silicate under compression, which suggested that the incompressibility of calcium silicate hydrates at atomistic scale was enhanced by the incorporation of fly ash into it. This was likely to be caused by the increased silicate polymerization of calcium silicate hydrates, which was attributed to the increase in the amount of silicate in their structure via the addition of fly ash.

Evaluation of a deep learning-based pelvic synthetic CT generation technique for MRI-based prostate proton treatment planning

The purpose of this work is to validate the application of a deep learning-based method for pelvic synthetic CT (sCT) generation that can be used for prostate proton beam therapy treatment planning. We propose to integrate dense block minimization into 3D cycle-consistent generative adversarial networks (cycleGAN) framework to effectively learn the nonlinear mapping between MRI and CT pairs. A cohort of 17 patients with co-registered CT and MR pairs were used to test the deep learning-based sCT generation method by leave-one-out cross-validation. Image quality between the sCT and CT images, gamma analysis passing rate, dose-volume metrics, distal range displacement, and the individual pencil beam Bragg peak shift between sCT- and CT-based proton plans were evaluated. The average mean absolute error (MAE) was 51.32 ± 16.91 HU. The relative differences of the statistics of the PTV dose-volume histogram (DVH) metrics in between sCT and CT were generally less than 1%. Mean values of dose difference, absolute dose difference (in percent of the prescribed dose) were −0.07% ± 0.07% and 0.23% ± 0.08%. Mean gamma analysis pass rate of 1 mm/1%, 2 mm/2%, 3 mm/3% criteria with 10% dose threshold were 92.39% ± 5.97%, 97.95% ± 2.95% and 98.97% ± 1.62% respectively. The median, mean and standard deviation of absolute maximum range differences were 0.09 cm and 0.23 ± 0.25 cm. The median and mean Bragg peak shifts among the 17 patients were 0.09 cm and 0.18 ± 0.07 cm. The image similarity, dosimetric and distal range agreement between sCT and original CT suggests the feasibility of further development of an MRI-only workflow for prostate proton radiotherapy.

MRI-based Proton Radiotherapy for Prostate Cancer Using Deep Convolutional Neural Networks

The purpose of this study is to develop a deep-learning-based method to generate synthetic CT (sCT) from anatomical MRI for potential MRI-only based prostate proton beam radiotherapy. We propose a 3D cycle-generative adversarial network (cycle-GAN) framework with dense blocks to effectively generate sCT from MRI. Cycle-GANs not only train the network from MRI to sCT, but also inversely reinforce the algorithm by generating cycle-MRI from sCT. To minimize the differences between the synthetic/cycle images and their respective real datasets, both transformations are implemented by a generator and the outputs are judged by a discriminator. Training the generator takes into account the estimation error loss as well as the discriminator feedback, which can make the generator’s output more similar to the real dataset and improve the discriminator’s ability to differentiate synthetic/cycle from real images. In the synthetic stage, the patches from testing MRI are fed into the well-trained transformation model to estimate the sCT patches. The full sCT is then generated through a patch fusion process. The sCT generation method was evaluated using 20 prostate cancer patients with 17 proton treatment plans. Our sCTs were registered to CT for generating MRI-based proton treatment plan. Mean absolute error (MAE) and normalized cross-correlation (NCC) were used to quantify the differences between the sCT and CT. Clinically-relevant dose volume histogram (DVH) metrics were extracted from CT- and sCT-based proton plans for quantitative dosimetric evaluation. Gamma analyses were performed for the comparison of planar dose distributions. Proton distal range displacement, and the individual pencil beam Bragg peak shift between both proton plans were also evaluated. The mean MAE and NCC between the sCT and CT were 50.89±16.79 HU and 0.93±0.03 for the entire cohort. Relative differences of the prostate DVH metrics between sCT and CT were less than 1%. Mean values of dose difference, absolute dose difference (in percent of the prescribed dose) were -0.07±0.07% and 0.23±0.08%. Mean gamma analysis pass rate was 99% using 3mm/3% criteria with 10% dose threshold. Median and mean absolute maximum range differences were 0.9 mm and 2.3 mm. Median and mean proton pencil beam spot Bragg peak shifts among all patients were 0.9 mm and 1.8 mm. We developed a novel deep-learning-based approach to generate sCT from routine MR for MRI-based proton radiotherapy. The proposed method reliably generated sCT from the MRI that provided dose calculation of comparable accuracy to the CT for proton treatment planning. Results of image quality, gamma analysis passing rate, DVH metrics, distal range displacement, and the individual pencil beam Bragg peak shift between two proton plans support further development of an MRI-only workflow for prostate proton radiotherapy.

A Simulation Study on Estimation of Bragg-Peak Shifts via Machine Learning Using Proton-Beam Images Obtained by Measurement of Secondary Electron Bremsstrahlung

We investigated an estimation method of Bragg-peak shifts via machine learning using proton-beam images obtained by measurement of secondary electron bremsstrahlung (SEB) by Monte Carlo simulation. Proton beams having energy of 139 MeV were incident on a water phantom with randomly placed air spheres inside, and 6400 pairs of “proton-beam images” and “a Bragg-peak shift” were prepared and then multiple linear regression analysis was carried out. A good agreement was found between the actual Bragg-peak shifts and predicted values in both the training and test sets. The coefficients of determination of the obtained prediction model were 0.899 for the training set and 0.894 for the test set. Consequently, we found that a prediction model with small variance and high prediction performance could be obtained using the SEB data.

Temperature and pH sensor based on functionalized magnetic nanofluid

Here we report a new simple colorimetric sensing platform based on magnetic nanofluid for rapid detection of temperature and pH. The new sensing platform relies on changes in the conformation of the adsorbed macromolecular functional groups and the consequent changes in the optical properties of magnetically polarizable nanoemulsion. By biasing the sensor with a weak magnetic field, nanoemulsion self assembled to form one dimensional grating with a fixed interdroplet spacing, which is sensitive to temperature or pH, depending on the functional groups attached. The sensing action is based on the subtle changes in the interdroplet spacing that is manifested from the reflected Bragg peak shift in the visible wavelength regime. Owing to temperature and pH response of poly(vinyl alcohol – vinyl acetate) (PVA-vac) and polyacrylic acid (PAA) respectively, they are used as functional moieties. The sensor showed a linear temperature and pH response between 5 and 90 °C and 3–11.5, respectively. These results suggest that a simple coupling of magnetic nanoemulsion with suitable adsorbed moieties offers a rapid sensing platform for temperature and pH. Further, by suitably changing the functional moieties, this approach can be extended to a variety of sensing applications, including visual detection.

A spectroscopic approach to probe macromolecular conformational changes at interface under different environmental conditions: A case study with PAA adsorbed at oil-water Interface

Knowledge of the behavior of adsorbed macromolecules at liquid-liquid interface under different physio-chemical conditions is extremely important in different scientific disciplines such as colloidal formulations, food, cosmetic materials, drug delivery systems, anti-bacterial surfaces etc. The conformational changes of a weak polyelectrolyte, polyacrylic acid (PAA), adsorbed at a magnetically controllable oil-water interface under different local environmental condition is manifested from the Bragg peak shifts in the reflected light, after the droplets are assembled into a periodic 1D array with the aid of a weak magnetic field. The change in Bragg peak wavelength was large when the adsorbed PAA molecular weight was high. Further, the conformational changes are also confirmed from force-distance and light scattering measurements. The intermolecular force measurement shows that the adsorbed PAA undergoes a reversible conformational change from a compact globule at pH~3 to an extended structure at pH~11, with a huge change in the interdroplet spacing due to an enhanced ionization of surface groups. With further increase in pH, the extended PAA is fully collapsed due to counter-ion condensation, resulting in an irreversible aggregation. The force and light scattering measurements further confirm the conformational change from globule to extended transition. This new spectroscopic approach offers promising applications in probing macromolecular conformation at interfaces and to obtain new insight into colloidal stability.

Laser Interference Lithography for the Nanofabrication of Stimuli‐Responsive Bragg Stacks

AbstractDynamic structural coloration in Tmesisternus isabellae beetle elytra is a unique example of Bragg stack‐based wavelength tuning in response to external stimuli. The underlying principles could guide the design of quantitative optical stimuli‐responsive polymers. Existing nanofabrication techniques to create such materials are costly, time‐consuming, and require high expertise. This study reports a nanofabrication method to produce slanted Bragg stack structures in poly(acrylamide‐co‐poly(ethylene glycol) diacrylate) hydrogel films by combining laser interference lithography and silver halide chemistry in a cost‐effective and rapid process (≈10 min). The Bragg stacks consist of silver bromide nanocrystal multilayers having a lattice spacing of ≈200 nm. Upon broadband light illumination, the Bragg stacks diffract a narrow‐band peak at 520 nm at ≈10° with respect to the normal incidence. The lattice spacing of the hydrogel films can be modulated by external stimuli to shift the Bragg peak for dynamic quantitative measurements. To demonstrate the utility of this method, the Bragg stacks are functionalized with phenylboronic acid molecules. Bragg peak shift analysis allows reversible glucose sensing within a physiological dynamic range (0.0–20.0 mmol L−1) having a sensitivity of 0.2 mmol L−1. The developed Bragg stacks may have application in portable, wearable, and implantable real‐time medical diagnostics at point‐of‐care settings.

Pair distribution function analysis of nanostructural deformation of calcium silicate hydrate under compressive stress

AbstractDespite enormous interest in calcium silicate hydrate (C–S–H), its detailed atomic structure and intrinsic deformation under an external load are lacking. This study demonstrates the nanostructural deformation process of C–S–H in tricalcium silicate (C3S) paste as a function of applied stress by interpreting atomic pair distribution function (PDF) based on in situ X‐ray scattering. Three different strains in C3S paste under compression were compared using a strain gauge, Bragg peak shift, and the real space PDF. PDF refinement revealed that the C–S–H phase mostly contributed to PDF from 0 to 20 Å whereas crystalline phases dominated that beyond 20 Å. The short‐range atomic strains exhibited two regions for C–S–H: I) plastic deformation (0‐10 MPa) and II) linear elastic deformation (&gt;10 MPa), whereas the long‐range deformation beyond 20 Å was similar to that of Ca(OH)2. Below 10 MPa, the short‐range strain was caused by the densification of C–S–H induced by the removal of interlayer or gel‐pore water. The strain is likely to be recovered when the removed water returns to C–S–H.

Transient Melting and Recrystallization of Semiconductor Nanocrystals Under Multiple Electron-Hole Pair Excitation.

Ultrafast optical pump, X-ray diffraction probe experiments were performed on CdSe nanocrystal (NC) colloidal dispersions as functions of particle size, polytype, and pump fluence. Bragg peak shifts related to heating and peak amplitude reduction associated with lattice disordering are observed. For smaller NCs, melting initiates upon absorption of as few as ∼15 electron-hole pair excitations per NC on average (0.89 excitations/nm3 for a 1.5 nm radius) with roughly the same excitation density inducing melting for all examined NCs. Diffraction intensity recovery kinetics, attributable to recrystallization, occur over hundreds of picoseconds with slower recoveries for larger particles. Zincblende and wurtzite NCs revert to initial structures following intense photoexcitation suggesting melting occurs primarily at the surface, as supported by simulations. Electronic structure calculations relate significant band gap narrowing with decreased crystallinity. These findings reflect the need to consider the physical stability of nanomaterials and related electronic impacts in high intensity excitation applications such as lasing and solid-state lighting.

Multi-stimuli responsive nanofluid with easy-to-visualize structural color patterns

We present the details of a multi- stimuli responsive nanofluid with easy-to-visualize structural color patterns. We have used a thermo-responsive polymer, Poly (N-isopropylacrylamide)(PNIPAM) and superparamagnetic nanoparticle to realize both thermal and magnetic actuation of the nanofluid. PNIPAM molecules adsorbed at the oil-water (O/W) interface acts as a stabilizer cum thermo-responsible moiety, while the superparamagnetic nanoparticles make the nanofluid magnetically responsive. Under a constant magnetic field and in the temperature range of 5–30°C, the interdroplet separation is reversibly tuned from 82 to 52nm. The reversible swelling and collapse of polymer adsorbed at the O/W interface is manifested from the Bragg peak shift at a constant magnetic force. Above the lower critical solution temperature (>35°C), a strong attraction between adsorbed PNIPAM layers caused the bridging of PNIPAM covered droplets, which was evident from the disappearance of Bragg peak after the removal of magnetic stimulus and the presence of bridged long flexible chains of drops. It is observed that the incorporation of a small amount of anionic surfactant monomers dramatically increases the volume phase transition, the repulsive interaction forces and the interparticle tunability due to strong association of PNIPAM and sodium dodecyl suphate (SDS). Our results suggest that by using PNIPAM and an anionic surfactant, the interparticle interactions and optical properties of magnetically polarizable nanofluids can be reversibly tuned. Thermo-magneto responsive nanoemulsions offer exciting applications in optical devices (2D and 3D photonic crystals, optical gratings, body temperature sensor etc.), smart drug delivery systems and sensors. Besides, they are wonderful model system to probe temperature induced conformational changes under different physiological conditions.

Inter-comparison of relative stopping power estimation models for proton therapy

Theoretical stopping power values were inter-compared for the Bichsel, Janni, ICRU and Schneider relative stopping power (RSP) estimation models, for a variety of tissues and tissue substitute materials taken from the literature. The RSPs of eleven plastic tissue substitutes were measured using Bragg peak shift measurements in water in order to establish a gold standard of RSP values specific to our centre’s proton beam characteristics. The theoretical tissue substitute RSP values were computed based on literature compositions to assess the four different computation approaches. The Bichsel/Janni/ICRU approaches led to mean errors in the RSP of −0.1/+0.7/−0.8%, respectively. Errors when using the Schneider approach, with I-values from the Bichsel, Janni and ICRU sources, followed the same pattern but were generally larger. Following this, the mean elemental ionisation energies were optimized until the differences between theoretical RSP values matched measurements. Failing to use optimized I-values when applying the Schneider technique to 72 human tissues could introduce errors in the RSP of up to −1.7/+1.1/−0.4% when using Bichsel/Janni/ICRU I-values, respectively. As such, it may be necessary to introduce an additional step in the current stoichiometric calibration procedure in which tissue insert RSPs are measured in a proton beam. Elemental I-values can then optimized to match these measurements, reducing the uncertainty when calculating human tissue RSPs.

Performance of MACACO Compton telescope for ion-beam therapy monitoring: first test with proton beams

In order to exploit the advantages of ion-beam therapy in a clinical setting, delivery verification techniques are necessary to detect deviations from the planned treatment. Efforts are currently oriented towards the development of devices for real-time range monitoring. Among the different detector concepts proposed, Compton cameras are employed to detect prompt gammas and represent a valid candidate for real-time range verification. We present the first on-beam test of MACACO, a Compton telescope (multi-layer Compton camera) based on lanthanum bromide crystals and silicon photo-multipliers. The Compton telescope was first characterized through measurements and Monte Carlo simulations. The detector linearity was measured employing 22Na and Am-Be sources, obtaining about 10% deviation from linearity at 3.44 MeV. A spectral image reconstruction algorithm was tested on synthetic data. Point-like sources emitting gamma rays with energy between 2 and 7 MeV were reconstructed with 3–5 mm resolution. The two-layer Compton telescope was employed to measure radiation emitted from a beam of 150 MeV protons impinging on a cylindrical PMMA target. Bragg-peak shifts were achieved via adjustment of the PMMA target location and the resulting measurements used during image reconstruction. Reconstructed Bragg peak profiles proved sufficient to observe peak-location differences within 10 mm demonstrating the potential of the MACACO Compton Telescope as a monitoring device for ion-beam therapy.

SU‐F‐J‐208: Prompt Gamma Imaging‐Based Prediction of Bragg Peak Position for Realistic Treatment Error Scenarios

Purpose:To quantify the accuracy in predicting the Bragg peak position using simulated in‐room measurements of prompt gamma (PG) emissions for realistic treatment error scenarios that combine several sources of errors.Methods:Prompt gamma measurements by a knife‐edge slit camera were simulated using an experimentally validated analytical simulation tool. Simulations were performed, for 143 treatment error scenarios, on an anthropomorphic phantom and a pencil beam scanning plan for nasal cavity. Three types of errors were considered: translation along each axis, rotation around each axis, and CT‐calibration errors with magnitude ranging respectively, between −3 and 3 mm, −5 and 5 degrees, and between −5 and +5%. We investigated the correlation between the Bragg peak (BP) shift and the horizontal shift of PG profiles. The shifts were calculated between the planned (reference) position and the position by the error scenario. The prediction error for one spot was calculated as the absolute difference between the PG profile shift and the BP shift.Results:The PG shift was significantly and strongly correlated with the BP shift for 92% of the cases (p&lt;0.0001, Pearson correlation coefficient R&gt;0.8). Moderate but significant correlations were obtained for all cases that considered only CT‐calibration errors and for 1 case that combined translation and CT‐errors (p&lt;0.0001, R ranged between 0.61 and 0.8). The average prediction errors for the simulated scenarios ranged between 0.08±0.07 and 1.67±1.3 mm (grand mean 0.66±0.76 mm). The prediction error was moderately correlated with the value of the BP shift (p=0, R=0.64). For the simulated scenarios the average BP shift ranged between −8±6.5 mm and 3±1.1 mm. Scenarios that considered combinations of the largest treatment errors were associated with large BP shifts.Conclusion:Simulations of in‐room measurements demonstrate that prompt gamma profiles provide reliable estimation of the Bragg peak position for complex error scenarios.Yafei Xing and Luiza Bondar are funded by BEWARE grants from the Walloon Region.The work presents simulations results for a prompt gamma camera prototype developed by IBA.

Nanostructural Deformation Analysis of Calcium Silicate Hydrate in Portland Cement Paste by Atomic Pair Distribution Function

The deformation of nanostructure of calcium silicate hydrate (C-S-H) in Portland cement (PC) paste under compression was characterized by the atomic pair distribution function (PDF), measured using synchrotron X-ray diffraction. The PDF of the PC paste exhibited a unique deformation behavior for a short-range order below 2.0 nm, close to the size of the C-S-H globule, while the deformation for a long-range order was similar to that of a calcium hydroxide phase measured by Bragg peak shift. The compressive deformation of the C-S-H nanostructure was comprised of three stages with different interactions between globules. This behavior would originate from the granular nature of C-S-H, which deforms with increasing packing density by slipping the interfaces between globules, rearranging the overall C-S-H nanostructure. This new approach will lead to increasing applications of the PDF technique to understand the deformation mechanism of C-S-H in PC-based materials.

SU‐E‐T‐553: Monte Carlo Calculation of Proton Bragg Peak Displacements in the Presence of Al2O3:C Dosimeters

Purpose:The application of optically stimulated luminescence dosimeters (OSLDs) may be extended to clinical investigations verifying irradiated doses in small animal models. In proton beams, the accurate positioning of the Bragg peak is essential for tumor targeting. The purpose of this study was to estimate the displacement of a pristine Bragg peak when an Al2O3:C nanodot (Landauer, Inc.) is placed on the surface of a water phantom and to evaluate corresponding changes in dose.Methods:Clinical proton pencil beam simulations were carried out with using TOPAS, a Monte Carlo platform layered on top of GEANT4. Point‐shaped beams with no energy spread were modeled for energies 100MV, 150MV, 200MV, and 250MV. Dose scoring for 100,000 particle histories was conducted within a water phantom (20cm × 20cm irradiated area, 40cm depth) with its surface placed 214.5cm away from the source. The modeled nanodot had a 4mm radius and 0.2mm thickness.Results:A comparative analysis of Monte Carlo depth dose profiles modeled for these proton pencil beams did not demonstrate an energy dependent in the Bragg peak shift. The shifts in Bragg Peak depth for water phantoms modeled with a nanodot on the phantom surface ranged between 2.7 to 3.2 mm. In all cases, the Bragg Peaks were shifted closer to the irradiation source. The peak dose in phantoms with an OSLD remained unchanged with percent dose differences less than 0.55% when compared to phantom doses without the nanodot.Conclusion:Monte Carlo calculations show that the presence of OSLD nanodots in proton beam therapy will not change the position of a pristine Bragg Peak by more than 3 mm. Although the 3.0 mm shift will not have a detrimental effect in patients receiving proton therapy, this effect may not be negligible in dose verification measurements for mouse models at lower proton beam energies.