eMC Algorithm Research Articles

Curvature correction factors for the independent verification of monitor units of electron treatment plans calculated in Eclipse.

Electron beam dosimetry is sensitive to the surface contour of the patient. Over 10% difference between Treatment Planning System (TPS) and independent monitor-unit (IMU) calculations have been reported in the literature. Similar results were observed in our clinic between Radformation ClearCalc IMU and Eclipse TPS electron Monte Carlo (eMC) algorithm (v.16.1). This paper presents data measured under 3D printed spherical and cylindrical phantoms to validate the eMC algorithm in the presence of curved geometries. Measurements were performed with multiple detectors and compared to calculations made in Eclipse for the 6, 9 and 12MeV electron energies. This data is used to create curvature correction factors (CCFs), defined as the ratio of the detector reading with the curved-surface phantom to a flat phantom at the same depth. The mean difference between the TPS calculated and measured CCFs using the NACP, Diode E, microSilicon, and microDiamond detectors were 1.3, 0.9, 0.7 and 0.7% respectively, with maximum differences of 4.5, 2.3, 1.9, and 1.8% respectively. Applying CCFs to previous failing patient IMU calculations improved agreement to the TPS. CCFs were implemented in our clinic for patient-specific IMU calculations with the assistance of a ESAPI script.

Commissioning and initial validation of Eclipse eMC algorithm for the electron FLASH research extension (FLEX) system for pre-clinical studies.

To investigate the feasibility of commissioning the 16 MeV electron FLASH Extension (FLEX) in the commercial treatment planning system (TPS) for biomedical research with cell and mouse models, and in silico treatment planning studies. To commission the FLEX system with the electron Monte Carlo (eMC) algorithm in the commercial TPS, radiochromic film was used to measure the vendor-recommended beam data. Once the beam model was generated for the eMC algorithm, supplemental measurements were collected for validation purposes and compared against the TPS-calculated results. Additionally, the newly commissioned 16 MeV FLASH beam was compared to the corresponding 16 MeV conventional electron beam. The eMC algorithm effectively modeled the FLEX system. The eMC-calculated PDDs and profiles for the 16 MeV electron FLASH beam agreed with measured values within 1%, on average, for 6×6 cm2 and 10×10cm2 applicators. Flatness and symmetry deviated by less than 1%, while FWHM and penumbra agreed within 1mm for both eMC-calculated and measured profiles. Additionally, the small field (i.e., 2-cm diameter cutout) that was measured for validation purposes agreed with TPS-calculated results within 1%, on average, for both the PDD and profiles. The FLASH and conventional dose rate 16 MeV electron beam were in agreement in regard to energy, but the profiles for larger field sizes began to deviate(>10×10cm2) due to the forward-peaked nature of the FLASH beam. For cell irradiation experiments, the measured and eMC-calculated in-plane and cross-plane absolute dose profiles agreed within 1%, on average. The FLEX system was successfully commissioned in the commercial TPS using the eMC algorithm, which accurately modeled the forward-peaked nature of the FLASH beam. A commissioned TPS for FLASH will be useful for pre-clinical cell and animal studies, as well as in silico FLASH treatment planning studies for future clinical implementation.

Optimal values of the Electron Monte Carlo dose engine parameters.

The aim of this study was to indicate the most favorable - in terms of to the time of calculation and the uncertainty of determining the dose distribution - values of the parameters for the Electron Monte Carlo (eMC) algorithm in the Eclipse treatment planning system. Using the eMC algorithm and the variability of the values of its individual parameters, calculations of the electron dose distribution in the full-scattering virtual water phantom were performed, obtaining percentage depth doses, beam profiles, absolute dose values in points and calculation times. The reference data included water tank measurements such as relative dose distributions and absolute point doses. For 63 sets of calculation data created from selected values of the parameters for the eMC algorithm, calculation times were analyzed and the absolute calculated and measured doses were compared. Performing a statistical analysis made it possible to determine whether the differences in the values of deviations between the actual dose and the calculated dose in individual regions of the percentage depth dose curve and the beam profile are statistically significant between the analyzed sets of parameters. Taking into account obtained results from the analysis of the discrepancy between the distribution of the calculated and measured dose, the correspondence of the absolute value of the calculated and measured dose and the duration of the calculation of the dose distribution, the optimal set of parameters was indicated for the eMC algorithm which allows obtaining the dose distribution and the number of monitor units in an acceptable time.

Quantitative evaluation of dosimetric uncertainties associated with small electron fields

IntroductionAlthough many studies have investigated small electron fields, there are several dosimetric issues that are not well understood. This includes lack of charged particle equilibrium, lateral scatter, source occlusion and volume averaging of the detectors used in the measurement of the commissioning data. High energy electron beams are also associated with bremsstrahlung production that contributes to dose deposition, which is not well investigated, particularly for small electron fields. The goal of this work has been to investigate dosimetric uncertainties associated with small electron fields using dose measurements with different detectors as well as calculations with eMC dose calculation algorithm. MethodsDifferent dosimetric parameters including output factors, depth dose curves and dose profiles from small electron field cutouts were investigated quantitatively. These dosimetric parameters were measured using different detectors that included small ion chambers and diodes for small electron cutouts with diameters ranging from 15-50mm mounted on a 6 × 6cm2 cone with beam energies from 6-20MeV. ResultsLarge deviations existed between the output factors calculated with the eMC algorithm and measured with small detectors for small electron fields up to 55% for 6MeV. The discrepancy between the calculated and measured doses increased 10%-55% with decreasing electron beam energy from 20 MeV to 6 MeV for 15mm circular field. For electron fields with cutouts 20mm and larger, the measured and calculated doses agreed within 5% for all electron energies from 6-20MeV. For small electron fields, the maximal depth dose shifted upstream and becomes more superficial as the electron beam energy increases from 6-20MeV as measured with small detectors. DiscussionLarge dose discrepancies were found between the measured and calculated doses for small electron fields where the eMC underestimated output factors by 55% for small circular electron fields with a diameter of 15 mm, particularly for low energy electron beams. The measured entrance doses and dmax of the depth dose curves did not agree with the corresponding values calculated by eMC. Furthermore, the measured dose profiles showed enhanced dose deposition in the umbra region and outside the small fields, which mostly resulted from dose deposition from the bremsstrahlung produced by high energy electrons that was not accounted for by the eMC algorithm due to inaccurate modeling of the lateral dose deposition from bremsstrahlung. ConclusionElectron small field dosimetry require more consideration of variations in beam quality, lack of charged particle equilibrium, lateral scatter loss and dose deposition from bremsstrahlung produced by energetic electron beams in a comprehensive approach similar to photon small field dosimetry. Furthermore, most of the commercially available electron dose calculation algorithms are commissioned with large electron fields; therefore, vendors should provide tools for the modeling of electron dose calculation algorithms for small electron fields.

Electron Beam Measurements Employing Electron Montecarlo Algorithm on TrueBeam STx® and Clinac iX® Linear Accelerators

Electron beam measurement comparison between TrueBeam STx® and Clinac iX® established. Data evaluation of eMC-calculated and measured for TrueBeam STx® performed. Dosimetric parameters measured including depth dose curves for each applicator, percentage depth dose (PDDs) curves without applicator, the profile in-air for a large field size 40×40 cm2, and the Absolute Dose (cGy/MU) for each applicator using a large water phantom (PTW, Freiburg, Germany), employing Roos and Markus plane-parallel ionization chambers. The data were examined for five electron beams of Varian’s TrueBeam STx® and Clinac iX® machines. A comparison between measurement PDDs and calculated by the Eclipse electron Monte Carlo (eMC) algorithm was performed to validate Truebeam STx® commissioning. The measured data indicated that electron beam PDDs from the TrueBeam STx® machine are well matched to those from Clinac iX® machine. The quality index R50 for applicator 15×15 cm2 was in the tolerance intervals. However, Surface dose (Ds) increases with increasing energy for both accelerators. Comparisons between the measured and eMC-calculated values revealed that the R100, R90, R80, and R50 values mostly agree within 5 mm. Measured and calculated bremsstrahlung tail Rp correlates well statistically. Ds agrees mostly within 2%. Electron beams were successfully validated for TrueBeam STx®, a good agreement between modeled and measured data was observed.

Quantitative evaluation of dosimetric uncertainties in electron therapy by measurement and calculation using the electron Monte Carlo dose algorithm in the Eclipse treatment planning system.

In the electron beam radiation therapy, customized blocks are mostly used to shape treatment fields to generate conformal doses. The goal of this study is to investigate quantitatively dosimetric uncertainties associated with heterogeneities, detectors used in the measurement of the beam data commissioning, and modeling of the interactions of high energy electrons with tissue. These uncertainties were investigated both by measurements with different detectors and calculations using electron Monte Carlo algorithm (eMC) in the Eclipse treatment planning system. Dose distributions for different field sizes were calculated using eMC and measured with a multiple‐diode‐array detector (MapCheck2) for cone sizes ranging from 6 to 25 cm. The dose distributions were calculated using the CT images of the MapCheck2 and water‐equivalent phantoms. In the umbra region (<20% isodose line), the eMC underestimated dose by a factor of 3 for high energy electron beams due to lack of consideration of bremsstrahlung emitted laterally that was not accounted by eMC in the low dose region outside the field. In the penumbra (20%–80% isodose line), the eMC overestimated dose (40%) for high energy 20 MeV electrons compared to the measured dose with small diodes in the high gradient dose region. This was mainly due to lack of consideration of volume averaging of the ion chamber used in beam data commissioning which was input to the eMC dose calculation algorithm. Large uncertainties in the CT numbers (25%) resulted from the image artifacts in the CT images of the MapCheck2 phantom due to metal artifacts. The eMC algorithm used the electron and material densities extracted from the CT numbers which resulted large dosimetric uncertainties (10%) in the material densities and corresponding stopping power ratios. The dose calculations with eMC are associated with large uncertainties particularly in penumbra and umbra regions and around heterogeneities which affect the low dose level that cover nearby normal tissue or critical structures.

Commissioning Measurements of Electron Beam Using Montecarlo Algorithm on Truebeam STx® and Compariaon with Clinac iX Linear Accelerator

TrueBeam STx latest generation linear accelerators (linacs) installed at Sheikh Khalifa International University Hospital in Casablanca, Morocco. The aim of this is to present and compare the result of the Electron commissioning measurement on TrueBeam Stx and clinac iX installed at Sheikh Khalifa International University Hospital in Casablanca, Morocco. A compariaon of eMC calculations and measurements for TrueBeam Stx were evaluated. Dosimetric parameters are systematically measured using a large water phantom 3D scanning system MP3 Water Phantom (PTW, Freiburg, Germany). The data of the electron beams commissioning including depth dose curves for each applicator, depth dose curves without applicator and the profile in air for a large field size 40x 40cm2, and the Absolute Dose (cGy/MU) for each applicator. All the data were examined and compared for five electron beams (E6MeV, E9MeV, E12MeV, E16MeV and E20MeV) of Varian’s TrueBeam STx and Clinac iX machines. A comparison, between measurement PDDs and calculated by the Eclipse electron Monte Carlo (eMC) algorithm were performed to validate Truebeam Stx commissioning. All this measurements were performed with a Roos and Markus plane parallel chamber. Our measured data indicated that electron beam PDDs from the TrueBeam Stx machine are well matched to those from our Varian Clinac iX machine. Significant differences between TrueBeam and Clinac iX were found in in‐air profiles and open field output. Maximum depth dose for the TrueBeam Stx and Clinac iX for the following energies (6, 9, 12, 16, 20 MeV) are respectively (1.15; 1.89; 2.6; 3.1; and 2.35) and (1.24; 1.95; 2.70; 2.99 and 2.4cm). For the TrueBeam Stx and Clinac iX the quality index R50 for applicator 15x15 cm2 are in the tolerance intervals. Surface dose increases by increasing energy for both machines. The Absolute Dose (cGy/MU) calibrated for both machine in Dmax at 1cGy/MU for the reference field size cone 15x15 cm2. Bremsstrahlung tail Rp per energy levels as follows for the TrueBeam Stx : 6 MeV – 2.85 cm, 9 MeV – 4.28 cm, 12 MeV – 5.97 cm, 16 MeV – 7.88 cm and 20 MeV – 9.86 cm. and for the Clinac iX : 6 MeV – 2.86 cm, 9 MeV – 4.32 cm, 12 MeV – 5.96 cm, 16 MeV – 7.93 cm and 20 MeV – 10.08 cm. A good agreement between modeled and measured data is observed.

Dosimetric evaluation of electron beam Monte Carlo isodoses distribution based on thermoluminescent dosimetry

Electron beams are applied in radiotherapy treatments where superficialized doses are desirable as well as deeper tissues sparing. Monte Carlo method has been recently implemented in the TPS as the algorithm for electron beam isodoses calculation at the National Institute of Cancer in Brazil. This work comprises an additional method of evaluation of the isodoses generated by the TPS, considering the irradiation of a non-flat surface. A 6-Gy electron beam breast irradiation was planned and delivered to an anthropomorphic phantom into which 36 capsules with TLD100 were inserted. The TLD calibration curve was performed from 100 cGy to 700 cGy. In an overall analysis, eMC algorithm isodose distribution results agreed with TLD measured doses. 75% of measured data met the 5% accuracy criteria, which can be considered in good agreement with the recommended uncertainties involved in a radiotherapy treatment. Considered all collected data, 8 TLDs received extremely low doses and due to tissue attenuation of the electron beam, the TLD measurements might have additional uncertainties. If these data are not taken into account, 100% of the measured doses, considering the uncertainties, meet the 5% accuracy criteria. About the 3 methods for isodose smoothing available in the eMC algorithm, the low level of dose smoothing option provides the best matching with measured data, consisting of the most reliable option. Considering the AAPM recommendations eMC algorithm offers an accurate solution for isodoses calculation, within a 5% accuracy.

Low-signal limit of X-ray single particle diffractive imaging.

An outstanding question in X-ray single particle imaging experiments has been the feasibility of imaging sub 10-nm-sized biomolecules under realistic experimental conditions where very few photons are expected to be measured in a single snapshot and instrument background may be significant relative to particle scattering. While analyses of simulated data have shown that the determination of an average image should be feasible using Bayesian methods such as the EMC algorithm, this has yet to be demonstrated using experimental data containing realistic non-isotropic instrument background, sample variability and other experimental factors. In this work, we show that the orientation and phase retrieval steps work at photon counts diluted to the signal levels one expects from smaller molecules or with weaker pulses, using data from experimental measurements of 60-nm PR772 viruses. Even when the signal is reduced to a fraction as little as 1/256, the virus electron density determined using ab initio phasing is of almost the same quality as the high-signal data. However, we are still limited by the total number of patterns collected, which may soon be mitigated by the advent of high repetition-rate sources like the European XFEL and LCLS-II.

Comprehensive evaluation of electron radiation dose using beryllium oxide dosimeters at breast radiotherapy

AbstractIntroduction:In this study, the differences between calculated and measured dose values were then analysed to assess the performance, in terms of accuracy, of the tested treatment planning system (TPS) algorithms applied to calculate electron beam dose targeted and non-targeted the breast region.Materials and methods:The beryllium oxide (BeO) dosimeters placed on the female RANDO phantom were irradiated 12 MeV electron energy with medical linear accelerator and repeatedly read in the Risø thermoluminescence (TL)/optically stimulated luminescence (OSL) system via OSL method at least three times.Results:For electron treatment, one made quantitative comparisons of the dose distributions calculated by TPSs with those from the measurements by OSL at various points in the RANDO phantom.The mean dose measured from the dosimeters placed on the female RANDO phantom target left breast region was 160 cGy and non-target right breast region was 1·2 cGy. Analysis of Generalised Gaussian Pencil Beam (GGPB) and Electron Monte Carlo (eMC) algorithms for determined region mean point dose values, respectively, 174 and 164 cGy. Two algorithms for non-targeted region calculated same point dose values of 0·2 cGy.Conclusions:The results of this study showed that BeO dosimeters can be used with OSL method in radiotherapy applications and it is a very important tool for the determination of targeted/non-targeted absorbed dose.

Quality control of radiotherapy treatment plans with electrons

In this work the quality of the treatment planning generated by EclipseÒ commercial treatment planning system for electron beams of energy 9 and 20 MeV was verified and their accuracy in the calculation of dose distributions for several clinical situations was evaluated. Tests cases had been developed according to the Brazilian reality, having as reference the radiotherapy treatments carried out in the National Institute of the Cancer.The system developed for checking the quality of treatment planning systems with electrons was efficient in evaluating the Eclipse planning system by identifying the failures of their algorithms, especially in planning the isodose. The verification system has been validated against the Monte Carlo method and the experimental data with an ionization chamber and showed the shortcomings of generalized pencil beam and eMC algorithms.

Comparison of Monitor Unit between Electron Monte Carlo Algorithm by Different Dose Normalization Methods and Conventional Manual Calculation

The purpose of this study was to evaluate the discrepancy between the monitor unit (MU) calculated by different dose normalization methods in the electron Monte Carlo (eMC) algorithm and the conventional manual MU. In the water phantom condition, the manual MU obtained from the measured output factor was compared with the calculated MU by the eMC algorithm, using 24 different irradiation field shapes and several different energies of electron beam. In the breast boost condition, calculated MUs by both calculation methods were evaluated for 45 cases. As a result, the MUs computed by the eMC algorithm in the water phantom varied according to the dose normalization methods, and the mean±standard deviation of the difference between the manual and calculated MU were 1.1±1.4%, 0.0±1.0% and 0.4±1.2% in peak depth normalization (PN), no plan normalization (NPN) and 100% at body maximum (100%BM), respectively. In breast-boost cases, the MU difference between the manual and the calculated MU were 6.1±3.7%, 3.4±2.8% and 1.1±2.9% in PN, NPN and 100%BM, respectively. We revealed that the resultant MU calculated by eMC algorithm was dependent on the dose normalization method and the averaged differences exceeded 6% in PN, especially in breast boost condition. When using the eMC in the breast boost condition, it is desirable to select an appropriate dose normalization method according to dose prescription policies at each facility.

The commissioning and validation of Monaco treatment planning system on an Elekta VersaHD linear accelerator.

Accurate beam modeling is essential to help ensure overall accuracy in the radiotherapy process. This study describes our experience with beam model validation of a Monaco treatment planning system on a Versa HD linear accelerator. Data were collected such that Monaco beam models could be generated using three algorithms: collapsed cone (CC) and photon Monte Carlo (MC) for photon beams, and electron Monte Carlo (eMC) for electron beams. Validations are performed on measured percent depth doses (PDDs) and profiles, for open‐field point‐doses in homogenous and heterogeneous media, and for obliquely incident electron beams. Gamma analysis is used to assess the agreement between calculation and measurement for intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) plans, including volumetric modulated arc therapy for stereotactic body radiation therapy (VMAT SBRT). For all relevant conditions, gamma index values below 1 are obtained when comparing Monaco calculated PDDs and profiles with measured data. Point‐doses in a water medium are found to be within 2% agreement of commissioning data in 99.5% and 98.6% of the points computed by MC and CC, respectively. All point‐dose calculations for the eMC algorithm in water are within 4% agreement of measurement, and 92% of measurements are within 3%. In heterogeneous media of air and cortical bone, both CC and MC yielded better than 3% agreement with ion chamber measurements. eMC yielded 3% agreement to measurement downstream of air with oblique beams of up to 27°, 5% agreement distal to bone, and within 4% agreement at extended source to surface distance (SSD) for all electron energies except 6 MeV. The 6‐MeV point of measurement is on a steep dose gradient which may impact the magnitude of discrepancy measured. The average gamma passing rate for IMRT/VMAT plans is 96.9% (±2.1%) and 98.0% (±1.9%) for VMAT SBRT when evaluated using 3%/2 mm criteria. Monaco beam models for the Versa HD linac were successfully commissioned for clinical use.

34 Optimization of eMC algorithm parameters for dose calculation in electron

Introduction Monte Carlo algorithms model the transport of particles in matter with great precision considering all physical phenomena which can’t be realized by simple Pencil beam algorithms. Varian Medical System’s eMC algorithm have this stochastic nature but requires significant computing resources. In clinical use, parameters can be adjusted by the user to reduce the calculation time at the cost of dose distribution and monitor unit precision. This study aims to select the group of parameters allowing the best compromise. Methods The combinatorial study of eMC V13.5.35 algorithm parameters examines the accuracy, 1, 2 and 3%, the calculation grid size, 1.0, 1.5, 2.0 and 2.5 mm and the filter smoothing level, Low, Medium and Strong for energies 6, 9, 12 and 16 MeV and fields of 5, 10 and 15 cm2, for a total of 432 calculation plans. Percentage depth dose (PDD) and beam profile measured at zref are compared to reference measurements in water by gamma index calculation. Accuracy of monitor unit (UM) number is also evaluated. In addition to the standard fields, ten patient plans with custom cash are studied. Results Local gamma index with 3%/3 mm acceptance criteria of PDD decreases from 98 to 85% for Low to Strong filters only for E6 regardless of accuracy and calculation grid. Analysis with 2%/2 mm acceptance criteria confirms the same trend for E9 with degradation from 88% to 72%. The local gamma index with 3%/3 mm acceptance criteria of beam profiles does not vary by the grid size and accuracy. Analysis with 2%/2 mm acceptance criteria shows a negative effect of the Low filter with 50% of the results below the 95% threshold except for the 10 cm2 reference field. The differences between MU calculated and measured in a homogeneous water medium increased with Low to Strong filters from 0.8 to 3.0%. Calculation accuracy between 1 and 3% results in increasing differences up to 3.0%. There is no effect of the calculation grid size. Analyzes of calculated MU with custom cache show that the use of an accuracy of 1 or 2% for a 2 mm grid and a Low filter results in MU differences between measured less than 1%. Conclusions The 1%-1 mm-Low parameters provide the most accurate results but have the longest calculation time. The 2%-2 mm-Low parameters are a good compromise on the dose distribution and MU calculated while reducing the computation time by 20.

195. Electronic Brachytherapy in clinical practice: Implementation and comparison against conventional techniques and electron montecarlo algorithm

Purpose Electronic Brachytherapy (EBX), a technique that utilizes miniaturized X-Rays source, is gaining ground in radiotherapy treatment in presence of small superficial lesions. This work focuses on acceptance test, commissioning, clinical implementation and dosimetric features of the novel EBX system Esteya® (Elekta AB, Stockholm, Sweden). Methods Flatness and symmetry of X-ray beams have been evaluated according IEC60976 using a high definition 2D array equipped of liquid filled ionization chambers (SRS 1000, PTW, Germany). Half Value Layer (HVL), PDD and absolute dose have been measured for each applicator with a soft X-ray parallel plate chamber (T34013 PTW, Germany) and solid water according to IAEA TRS 398 [1] . Dose distributions have been compared with the ones calculated for conventional electron treatments. Calculations have been carried out in a virtual water phantom by electron montecarlo (eMc) algorithm implemented in a commercial TPS (Monaco v. 5.11, Elekta) for each applicator. Results Flatness, symmetry and penumbra showed excellent performance even if compared with eMC plans. Build up absence and PDDs slopes allow good homogeneity for coverage in superficial targets. Conclusions Shielding requirements, patient compliance and global management of Electronic brachytherapy sources are well known advantages [2] . This study demonstrated that EBX could be a valid alternative to electron treatment in case of small skin lesions also from a dosimetric point of view.

Characterisation of a MOSFET-based detector for dose measurement under megavoltage electron beam radiotherapy

The aim of this study is to investigate the fundamental dosimetric characteristics of the MOSkin detector for megavoltage electron beam dosimetry. The reproducibility, linearity, energy dependence, dose rate dependence, depth dose measurement, output factor measurement, and surface dose measurement under megavoltage electron beam were tested. The MOSkin detector showed excellent reproducibility (>98%) and linearity (R2= 1.00) up to 2000cGy for 4–20MeV electron beams. The MOSkin detector also showed minimal dose rate dependence (within ±3%) and energy dependence (within ±2%) over the clinical range of electron beams, except for an energy dependence at 4MeV electron beam. An energy dependence correction factor of 1.075 is needed when the MOSkin detector is used for 4MeV electron beam. The output factors measured by the MOSkin detector were within ±2% compared to those measured with the EBT3 film and CC13 chamber. The measured depth doses using the MOSkin detector agreed with those measured using the CC13 chamber, except at the build-up region due to the dose volume averaging effect of the CC13 chamber. For surface dose measurements, MOSkin measurements were in agreement within ±3% to those measured using EBT3 film. Measurements using the MOSkin detector were also compared to electron dose calculation algorithms namely the GGPB and eMC algorithms. Both algorithms were in agreement with measurements to within ±2% and ±4% for output factor (except for the 4 × 4cm2 field size) and surface dose, respectively. With the uncertainties taken into account, the MOSkin detector was found to be a suitable detector for dose measurement under megavoltage electron beam. This has been demonstrated in the in vivo skin dose measurement on patients during electron boost to the breast tumour bed.

Reconstructing three-dimensional protein crystal intensities from sparse unoriented two-axis X-ray diffraction patterns.

Recently, there has been a growing interest in adapting serial microcrystallography (SMX) experiments to existing storage ring (SR) sources. For very small crystals, however, radiation damage occurs before sufficient numbers of photons are diffracted to determine the orientation of the crystal. The challenge is to merge data from a large number of such 'sparse' frames in order to measure the full reciprocal space intensity. To simulate sparse frames, a dataset was collected from a large lysozyme crystal illuminated by a dim X-ray source. The crystal was continuously rotated about two orthogonal axes to sample a subset of the rotation space. With the EMC algorithm [expand-maximize-compress; Loh & Elser (2009). Phys. Rev. E, 80, 026705], it is shown that the diffracted intensity of the crystal can still be reconstructed even without knowledge of the orientation of the crystal in any sparse frame. Moreover, parallel computation implementations were designed to considerably improve the time and memory scaling of the algorithm. The results show that EMC-based SMX experiments should be feasible at SR sources.

Reconstruction of Three-Dimensional Structures of a Protein with Software ENMA and EMC Algorithm: A Simulation for XFEL-CXDI Experiment

Coherent X-ray diffraction imaging (CXDI) experiments enable us to visualize the structures of non-crystalline particles with micrometer to sub-micrometer dimensions. Using the X-ray free-electron laser (XFEL), two-dimensional diffraction patterns are collected in the diffraction-before-destruction scheme. To reconstruct three-dimensional electron density maps of a particle, it is necessary to classify the diffraction patterns in terms of structural polymorphism before the reconstruction. Here, we performed a simulation for XFEL-CXDI experiment of a protein predominantly adopting two states. After classifying the data using the custom-made software “ENMA” [1] in which the manifold theory is implemented, we successfully reconstructed the three-dimensional electron density maps of the states using the EMC algorithm [2].[1] T. Yoshidome, T. Oroguchi, M. Nakasako, and M. Ikeguchi, Phys. Rev. E 92, 032710 (2015).[2] N.-T. Duane Loh and V. Elser, Phys. Rev. E 80, 026705 (2009).

Verification measurements of an eMC algorithm using a 2D ion chamber array.

The aim of this study was to assess the suitability of the Im'RT MatriXX 2D ion chamber array for performing verification measurements on the Varian Eclipse electron Monte Carlo (eMC) algorithm for a range of clinical energies (6, 12, and 20 MeV) on a Varian 2100iX linear accelerator. Firstly, the suitability of the MatriXX for measuring percentage depth doses (PDD) in water was assessed, including characterization of the inherent buildup found in the MatriXX. Secondly the suitability of the MatriXX for measuring dose distributions in homogeneous and heterogeneous phantoms was assessed using gamma analysis at 3%/3 mm. It was found that after adjusting the PDD curves for the inherent buildup, that the position of R50,D measured using the MatriXX agreed to within 1 mm to the PDDs generated using the eMC algorithm for all energies used in this study. Gamma analysis at 3%/3 mm showed very good agreement (>95%) for all cases in both homogeneous and heterogeneous phantoms. It was concluded that the Im'RT MatriXX is a suitable device for performing eMC verification and could potentially be used for routine energy checks of electron beams.PACS number(s): 87.55.km, 87.55.Qr

Large-scale Monte Carlo simulations for the depinning transition in Ising-type lattice models

With the developed “extended Monte Carlo” (EMC) algorithm, we have studied the depinning transition in Ising-type lattice models by extensive numerical simulations, taking the random-field Ising model with a driving field and the driven bond-diluted Ising model as examples. In comparison with the usual Monte Carlo method, the EMC algorithm exhibits greater efficiency of the simulations. Based on the short-time dynamic scaling form, both the transition field and critical exponents of the depinning transition are determined accurately via the large-scale simulations with the lattice size up to L=8912, significantly refining the results in earlier literature. In the strong-disorder regime, a new universality class of the Ising-type lattice model is unveiled with the exponents β=0.304(5),ν=1.32(3),z=1.12(1), and ζ=0.90(1), quite different from that of the quenched Edwards–Wilkinson equation.