Full Monte Carlo Research Articles

Real Time Modelling of The Dose Distribution Adapted to The Present Treatment Requirements (TG186)

The current approach for brachytherapy usually relies on superposition of single sources in a homogeneous liquid water phantom. This technique is fast and practical in the clinical context but not adapted to the present treatment requirements (TG186[a]) The influence of tissue heterogeneities, inter-seed attenuation and finite patient dimensions, have to be considered. A full Monte-Carlo (MC) code allows computing the Dose Distribution (DD), with a high precision, but is usually too time consuming to be routinely used in clinical context. This work proposes a new method for accurately calculating the DD within a time compatible with clinical requirements.

Independent dose validation system for Gamma Knife radiosurgery, using a DICOM-RT interface and Geant4

Leksell GammaPlan was specifically designed for Gamma Knife (GK) radiosurgery planning, but it has limited accuracy for estimating the dose distribution in inhomogeneous areas, such as the embolization of arteriovenous malformations. We aimed to develop an independent patient dose validation system based on a patient-specific model, constructed using a DICOM-RT interface and the Geant4 toolkit. Leksell Gamma Knife Perfexion was designed in Geant4.10.00 and includes a DICOM-RT interface. Output factors for each collimator in a sector and dose distributions in a spherical water phantom calculated using a Monte Carlo (MC) algorithm were compared with the output factors calculated by the tissue maximum ratio (TMR) 10 algorithm and dose distributions measured using film, respectively. Studies using two types of water phantom and two patient simulation cases were evaluated by comparing the dose distributions calculated by the MC, the TMR and the convolution algorithms. The water phantom studies showed that if the beam size is small and the target is located in heterogeneous media, the dose difference could be up to 11%. In the two patient simulations, the TMR algorithm overestimated the dose by about 4% of the maximum dose if a complex and large bony structure was located on the beam path, whereas the convolution algorithm showed similar results to those of the MC algorithm. This study demonstrated that the in-house system could accurately verify the patient dose based on full MC simulation and so would be useful for patient cases where the dose differences are suspected.

A fast jaw-tracking model for VMAT and IMRT Monte Carlo simulations.

Modern radiotherapy techniques involve routine use of volumetric arc therapy (VMAT) and intensity modulated radiotherapy (IMRT) with jaw‐tracking – dynamic motion of the secondary collimators (jaws) in tandem with multi‐leaf collimators (MLCs). These modalities require accurate dose calculations for the purposes of treatment planning and dose verification. Monte Carlo (MC) methods for radiotherapy dose calculation are widely accepted as capable of achieving high accuracy. This paper presents an efficiency‐enhancement method for secondary collimator modeling, presented in the context of a tool for MC‐based dose second checks. The model constitutes an accuracy trade‐off in the source model for the sake of efficiency enhancement, but maintains the advantages of MC transport in patient heterogeneities. The secondary collimator model is called Flat‐Absorbing‐Jaw‐Tracking (FAJT). Transmission through and scatter from the secondary collimators is neglected, and jaws are modeled as perfectly absorbing planes. To couple the motion of secondary collimators with MLCs for jaw‐tracking, the FAJT model was built into the VCU‐MLC model. Gamma‐index analysis of the dose distributions from FAJT against the full BEAMnrc MC simulations showed over 99% pass rate for a range of open fields, two clinical IMRT, and one VMAT treatment plan, for 2%/2 mm criteria above 10%. Using FAJT, the simulation speed of the secondary collimators for open fields increased by a factor of 237, 1489, and 1395 for 4 × 4, 10 × 10, and 30 × 30 cm2, respectively. In general, clinically oriented simulation times are reduced from “hours” to “minutes” on identical hardware. Results for nine representative clinical cases (seven with jaw‐tracking) are presented. The average 2%/2 mm γ‐test success rate above the 80% isodose was 96.8% when tested against the EPIDose electronic portal image‐based dose reconstruction method and 97.3% against the Eclipse analytical anisotropic algorithm.

Hybrid fluid–kinetic neutral model based on a kinetic correction on a fluid solution

We describe a hybrid fluid–kinetic approach for the neutral particles in the plasma edge for a simplified 1D model. This is done by means of a micro–macro decomposition of the kinetic equation. The closure terms from the fluid (macro) equations are modelled with a Monte Carlo (MC) simulation of the kinetic (micro) equation. We assess two hybrid neutral models with different underlying fluid models: (a) a pure pressure diffusion equation and (b) a pressure diffusion equation superposed with an energy equation. Both hybrid models reduce the statistical errors on the resulting particle and momentum sources by about a factor five for a given computational time, whereas the statistical error on the energy source is reduced by about a factor three compared to the full kinetic MC simulation. The hybrid model without the fluid energy equation slightly outperforms the model with the energy equation for the prediction of the particle and momentum sources, but adding an energy equation to the fluid model is beneficial for reducing the statistical error on the energy source.

Comparison of Monte Carlo and analytical dose computations for intensity modulated proton therapy

To evaluate the effect of approximations in clinical analytical calculations performed by a treatment planning system (TPS) on dosimetric indices in intensity modulated proton therapy. TPS calculated dose distributions were compared with dose distributions as estimated by Monte Carlo (MC) simulations, calculated with the fast dose calculator (FDC) a system previously benchmarked to full MC. This study analyzed a total of 525 patients for four treatment sites (brain, head-and-neck, thorax and prostate). Dosimetric indices (D02, D05, D20, D50, D95, D98, EUD and Mean Dose) and a gamma-index analysis were utilized to evaluate the differences. The gamma-index passing rates for a 3%/3 mm criterion for voxels with a dose larger than 10% of the maximum dose had a median larger than 98% for all sites. The median difference for all dosimetric indices for target volumes was less than 2% for all cases. However, differences for target volumes as large as 10% were found for 2% of the thoracic patients. For organs at risk (OARs), the median absolute dose difference was smaller than 2 Gy for all indices and cohorts. However, absolute dose differences as large as 10 Gy were found for some small volume organs in brain and head-and-neck patients. This analysis concludes that for a fraction of the patients studied, TPS may overestimate the dose in the target by as much as 10%, while for some OARs the dose could be underestimated by as much as 10 Gy. Monte Carlo dose calculations may be needed to ensure more accurate dose computations to improve target coverage and sparing of OARs in proton therapy.

Abstract ID: 197 Monte Carlo simulations of X-ray grating interferometry based imaging systems

Over the last couple of years the implementation of Monte Carlo (MC) methods of grating based imaging techniques is of increasing interest. Several different approaches were taken to include coherent effects into MC in order to simulate the radiation transport of the image forming procedure. These include full MC using FLUKA [1], which however are only considering monochromatic sources. Alternatively, ray-tracing based MC [2] allow fast simulations with the limitation to provide only qualitative results, i.e. this technique is not suitable for dose calculation in the imaged object. Finally, hybrid models [3] were used allowing quantitative results in reasonable computation time, however only two-dimensional implementations are available. Thus, this work aims to develop a full MC framework for X-ray grating interferometry imaging systems using polychromatic sources suitable for large-scale samples. For this purpose the EGSnrc C++ MC code system is extended to take Snell's law, the optical path length and Huygens principle into account. Thereby the EGSnrc library was modified, e.g. the complex index of refraction has to be assigned to each region depending on the material. The framework is setup to be user-friendly and robust with respect to future updates of the EGSnrc package. These implementations have to be tested using dedicated academic situations. Next steps include the validation by comparisons of measurements for different setups with the corresponding MC simulations. Furthermore, the newly developed implementation will be compared with other simulation approaches. This framework will then serve as bases for dose calculation on CT data and has further potential to investigate the image formation process in grating based imaging systems.

2. Entropic closure for MRI-guided radiotherapy

Introduction The majority of patients affected by cancer are nowadays treated by radiotherapy, which consists in delivering a homogeneous dose with energetic particles. Magnetic Resonance Imaging (MRI)-guided radiotherapy shows precisely the tumor position in real time and allows to direct the photon beams to the tumor while sparing organs at risks. Our work consists in the validation of a new model developped to simulate the energy deposition of the particles used in radiotherapy (electrons, photons and protons) in the presence of strong magnetic field, within human tissues, and its adaptation to this new technology. Material and methods This model is based on a kinetic entropic closure of the linearized Boltzmann equation [1] , which describes the transport of energetic particles in the matter. This equation takes a lot of computation time to be solved due to the high number of variables. To simplify this, we replace fluences by angular moments, which allows getting rid of the angular variables and improve the calculation time. We obtain a set of angular moments equations, and we close this set using the Boltzmann’s principle of entropy maximization on the two first equations of the set. This model has an accuracy comparable to references Monte-Carlo (MC) codes [2] (Geant4, MCNPx, Penelope), and is less time-consuming than these ones. We added the Lorentz force into our code to study the influence of a magnetic field on the dose deposition, and compared it to the reference full MC code FLUKA. To further validate our model, we have carried out an experimental campaign in which we irradiated a composition of materials of different mass densities, with 6 and 18 MV photon beams of a Varian Clinac 21Ex accelerator, without and with the influence of a 0.87 T magnetic field of amplitude induced by a permanent magnet. Results We show a good agreement between our model and the FLUKA code ( Fig. 1 ). We highlight the effects that occur on the propagation of particles in the matter in presence of a magnetic field of a few Tesla. Indeed, it modifies the dose deposition by shifting the deposition of energy, leading to an increased diffusion depending on the orientation of the magnetic field. Moreover, it also leads to an increase or decrease of the dose deposited at the interfaces between materials depending on their difference between mass densities. The results of our experiments lead to the same conclusions. These effects have to be taken into account in order to prevent creation of hot spots or a spread of energy distribution in a human body, within computation times compatible with the clinical environment. Conclusion Our model is a good candidate for future Treatment Planning Systems since it allows a faster and efficient way to plan a viable treatment for a patient in presence of strong magnetic fields. A magnetic field modifies the profile of the dose deposition such as it has to be taken into account in calculations to prevent the dramatic changes which occur at interfaces between media of different density. This work takes place in the framework of POPRA (Programme Optique Physique et Radiotherapie en Aquitaine), which involves several laboratories around problematics on the topic of cancer treatment.

Abstract ID: 116 Comparison of beam output factors in MCNP6 and Geant4 based IAEA phase-space files

Monte Carlo (MC) dose calculation algorithms demand an accurate characterization of the radiation beam. At present, three MC-based beam models are commonly used for dose calculation; namely, full MC simulation, virtual source model, and phase space (phsp) files. The first two require detailed information of the LINAC head: information that is not always available from vendors. Therefore, properly validated phase-space data for external beam radiotherapy, available from the IAEA Nuclear Data Services section, remains a valuable alternative for MC beam simulation. The aim of this work is to compare the beam output factors obtained by MC-based phsp simulations in MCNP6 and Geant4. The simulations were performed with the photon mode energies of 6, 10, and 25 MV on the ELEKTA Precise. The simulations are divided into two steps: (1) the development of a method for directly reading the phase-space files provided by the IAEA in MCNP6, and (2) the determination of cut-off values, variation reduction techniques, and field size. Patient-specific beam line devices (blocks, jaws, wedges, etc.) were not simulated. The comparison of the output factors as percentage depth dose (PDD), lateral dose profiles, and dose distributions for different field sizes were computed using Geant4 and MCNP6. Both calculations generate matching PDD for a range of open-field sizes within the statistical uncertainties. Variation in lateral dose profiles varies up to 5% in the 25 MV energy mode. Comparison of dose distributions for an open 10 × 10 field by the gamma evaluation test returns a value of 0.93. Despite the lack of a user-friendly MCNP6 interface, this work shows that MCNP6 is suitable for beam simulation based IAEA-phsp.

Fast 3D Modeling of Dose Distribution in Brachytherapy Adapted to Recommendations of International Organizations of Medical Practice

The current approach for brachytherapy usually relies on superposition of single sources in a homogeneous liquid water phantom. This technique is fast and practical in the clinical context but not adapted to the present treatment requirements [Beaulieu et al, TG186, Med Phys. 39, 6208 (2012)]. The influence of tissue heterogeneities, inter-seed attenuation and finite patient dimensions, have to be considered. A full Monte-Carlo (MC) code allows computing the Dose Distribution (DD), with a high precision, but is too time consuming to be routinely used in clinical context. This work proposes a new method for accurately calculating the DD within a time compatible with clinical requirements. Our code solves the three dimensional linear Boltzmann transport equation (LBTE). The model is based on a multi-group energy approach combined with a specific angular momentum closure, deduced from the principle of entropy minimization. The code has been recently applied to external radio-therapy and results suggest that the method is as accurate as Monte-Carlo code for the considered test cases [1]. The transport, attenuation and scattering are based on microscopic cross sections in the energy range from a few keV up to Mev’s. All particles, electrons, positrons, photons, primary or secondary are treated simultaneously and computations are performed in full three-dimensional geometry. Our deterministic method differs from existing commercial software [2] by the phase space discretization and the LBTE solving. Our method has been tested by using water phantoms with tissues and density/material inserts. The DD’s computed with our deterministic model have been compared with full three-dimensional converging MC simulations. We demonstrated that the model is capable of reproducing the DD’s with accuracy of a few percent compared to the reference MC calculations. The deterministic model is fast and hence it may be a viable candidate for a future Treatment Planning System. Limitations and possible improvements of the deterministic method are presented. Photon energies are relatively low in brachytherapy and the contribution of scattered photons to the total dose can be of the same order of magnitude as the primary dose, particularly in the presence of inhomogeneities. In addition, for these energies, the photoelectric effect, specifically in the inter seed attenuation, yields deviation from an in-water DD. The proposed method provides a fast, accurate and integrated dose computation without any corrections or adjustments. In addition, the discretization of the space dimension is well suited to problems in radiation therapy where voxel-based geometries of patients are conducted from tomographic images.

Fred: a GPU-accelerated fast-Monte Carlo code for rapid treatment plan recalculation in ion beam therapy

Ion beam therapy is a rapidly growing technique for tumor radiation therapy. Ions allow for a high dose deposition in the tumor region, while sparing the surrounding healthy tissue. For this reason, the highest possible accuracy in the calculation of dose and its spatial distribution is required in treatment planning. On one hand, commonly used treatment planning software solutions adopt a simplified beam–body interaction model by remapping pre-calculated dose distributions into a 3D water-equivalent representation of the patient morphology. On the other hand, Monte Carlo (MC) simulations, which explicitly take into account all the details in the interaction of particles with human tissues, are considered to be the most reliable tool to address the complexity of mixed field irradiation in a heterogeneous environment. However, full MC calculations are not routinely used in clinical practice because they typically demand substantial computational resources. Therefore MC simulations are usually only used to check treatment plans for a restricted number of difficult cases. The advent of general-purpose programming GPU cards prompted the development of trimmed-down MC-based dose engines which can significantly reduce the time needed to recalculate a treatment plan with respect to standard MC codes in CPU hardware. In this work, we report on the development of fred, a new MC simulation platform for treatment planning in ion beam therapy. The code can transport particles through a 3D voxel grid using a class II MC algorithm. Both primary and secondary particles are tracked and their energy deposition is scored along the trajectory. Effective models for particle–medium interaction have been implemented, balancing accuracy in dose deposition with computational cost. Currently, the most refined module is the transport of proton beams in water: single pencil beam dose–depth distributions obtained with fred agree with those produced by standard MC codes within 1–2% of the Bragg peak in the therapeutic energy range. A comparison with measurements taken at the CNAO treatment center shows that the lateral dose tails are reproduced within 2% in the field size factor test up to 20 cm. The tracing kernel can run on GPU hardware, achieving 10 million primary on a single card. This performance allows one to recalculate a proton treatment plan at 1% of the total particles in just a few minutes.

Angular correlations in the prompt neutron emission in spontaneous fission of252Cf

An experiment aiming at the detailed investigation of angular correlations in the neutron emission from spontaneous fission of 252 Cf has been performed at IPHC Strasbourg using the angle-sensitive double ionization chamber CODIS for measuring fission fragments and a set of 60 DEMON scintillator counters for neutron detection. The main aim of the experiment is to search for an anisotropy of neutron emission in the center-of-mass system of the fragments. The present status of the data analysis and the full Monte-Carlo simulation of the experiment are reported in the present paper.

Evaluating the Application of Tissue-Specific Dose Kernels Instead of Water Dose Kernels in Internal Dosimetry: A Monte Carlo Study.

The aim of this work is to evaluate the application of tissue-specific dose kernels instead of water dose kernels to improve the accuracy of patient-specific dosimetry by taking tissue heterogeneities into consideration. Tissue-specific dose point kernels (DPKs) and dose voxel kernels (DVKs) for yttrium-90 (90Y), lutetium-177 (177Lu), and phosphorus-32 (32P) are calculated using the Monte Carlo (MC) simulation code GATE (version 7). The calculated DPKs for bone, lung, adipose, breast, heart, intestine, kidney, liver, and spleen are compared with those of water. The dose distribution in normal and tumorous tissues in lung, liver, and bone of a Zubal phantom is calculated using tissue-specific DVKs instead of those of water in conventional methods. For a tumor defined in a heterogeneous region in the Zubal phantom, the absorbed dose is calculated using a proposed algorithm, taking tissue heterogeneity into account. The algorithm is validated against full MC simulations. The simulation results indicate that the highest differences between water and other tissue DPKs occur in bone for 90Y (12.2% ± 0.6%), 32P (18.8% ± 1.3%), and 177Lu (16.9% ± 1.3%). The second highest discrepancy corresponds to the lung for 90Y (6.3% ± 0.2%), 32P (8.9% ± 0.4%), and 177Lu (7.7% ± 0.3%). For 90Y, the mean absorbed dose in tumorous and normal tissues is calculated using tissue-specific DVKs in lung, liver, and bone. The results are compared with doses calculated considering the Zubal phantom water equivalent and the relative differences are 4.50%, 0.73%, and 12.23%, respectively. For the tumor in the heterogeneous region of the Zubal phantom that includes lung, liver, and bone, the relative difference between mean calculated dose in tumorous and normal tissues based on the proposed algorithm and the values obtained from full MC dosimetry is 5.18%. A novel technique is proposed considering tissue-specific dose kernels in the dose calculation algorithm. This algorithm potentially enables patient-specific dosimetry and improves estimation of the average absorbed dose of 90Y in a tumor located in lung, bone, and soft tissue interface by 6.98% compared with the conventional methods.

A kernel-based dose calculation algorithm for kV photon beams with explicit handling of energy and material dependencies

Objective:Mimicking state-of-the-art patient radiotherapy with high-precision irradiators for small animals is expected to advance the understanding of dose–effect relationships and radiobiology in general. We work on the implementation of intensity-modulated radiotherapy-like irradiation schemes for small animals. As a first step, we present a fast analytical dose calculation algorithm for keV photon beams.Methods:We follow a superposition–convolution approach adapted to kV X-rays, based on previous work for microbeam therapy. We assume local energy deposition at the photon interaction point due to the short electron ranges in tissue. This allows us to separate the dose calculation into locally absorbed primary dose and the scatter contribution, calculated in a point kernel approach. We validate our dose model against Geant4 Monte Carlo (MC) simulations and compare the results to Muriplan (XStrahl Ltd, Camberley, UK).Results:For field sizes of (1 mm)2 to (1 cm)2 in water, the depth dose curves show a mean disagreement of 1.7% to MC simulations, with the largest deviations in the entrance region (4%) and at large depths (5% at 7 cm). Larger discrepancies are observed at water-to-bone boundaries, in bone and at the beam edges in slab phantoms and a mouse brain. Calculation times are in the order of 5 s for a single beam.Conclusion:The algorithm shows good agreement with MC simulations in an initial validation. It has the potential to become an alternative to full MC dose calculation.Advances in knowledge:The presented algorithm demonstrates the potential of kernel-based dose calculation for kV photon beams. It will be valuable in intensity-modulated radiotherapy and inverse treatment planning for high precision small-animal radiotherapy.

Monte-Carlo study of the MRPC prototype for the upgrade of BESIII

A GEANT4-based simulation is developed for the endcap time of flight (ETOF) upgrade based on multi-gap resistive plate chambers (MRPC) for the BESIII experiment. The MRPC prototype and the simulation method are described. Using a full Monte-Carlo simulation, the influence of high voltage and threshold on time resolution and detection efficiency are investigated. The preliminary results from simulation are presented and are compared with the experimental data taken with the prototype MRPC modules.

Examination of general cavity theory for magnesium and titanium doped lithium fluoride (TLD-100) of varying thicknesses in bone and lung

PurposeTo evaluate the accuracy of Burlin cavity theory for TLDs in bone and lung, the two most relevant heterogeneities in radiological physics. MethodsTheoretical calculations and Monte Carlo (MC) simulations of dose to TLD to dose to medium correction factor, (f)medTLD, were performed and compared in bone and lung. MC simulations included virtual irradiation of TLDs with varying thicknesses (0.015, 0.038, and 0.089 cm) in bone, lung, and water phantoms. Theoretical calculation of Burlin cavity theory requires calculation of fractional dose contribution from photon interactions (d) from mass effective attenuation coefficient (β) and average path length of electrons penetrating in the cavity from the wall (g). Different theoretical formulations of g and β were used to calculate 18 different values for d and (f)medTLD. Further, the impact of mean energy approximation used in theoretical calculations was evaluated using full spectrum MC simulations. ResultsWhile the values of d differed as much as by a factor of 2, (f)medTLD agreed well (SD = 0.1%) in water, bone and lung. The TLD thickness ranging 0.015–0.089 cm was not a significant factor (SD = 0.2%). Dose correction factors calculated using mean energy approximation agreed within the 2% with full spectrum MC simulations. Uncertainty associated with theoretical calculation of (f)medTLD was 7.2% compare to 0.5% with MC simulation. ConclusionThe (f)medTLD calculated with Burlin theory agreed well with MC results for 6 MV photon beam. Nevertheless, the difficulty and the ambiguity in the determination of β and g in a given medium and the energy spectrum under investigation limited the theoretical calculations and resulted in large uncertainty. This study suggests the use of MC for easy and accurate estimation of(f)medTLD, which is required in radiological applications to convert TLD measured dose to dose in medium.

Preliminary evaluation of the costs and benefits of prawn stocking to enhance recreational fisheries in recruitment limited estuaries

Hatchery-based fisheries enhancement involves supplementing natural recruitment through releases of cultured individuals to increase the productivity of wild harvest fisheries. The responsible approach to marine stock enhancement recommends economic assessment of enhancement endeavours be undertaken, but such assessments are difficult for recreational fisheries and consequently examples of such analyses are rare. This paper describes a bioeconomic assessment of hatchery releases to enhance a recreational Eastern King Prawn fishery in a recruitment limited coastal lake. Sensitivity analysis on the model indicated that parameters estimating growth and economic impact were the most important drivers of the model. A full Monte-Carlo Analysis of Uncertainty indicated that a scenario releasing 3,000,000 Eastern King Prawn postlarvae is most likely to yield over 5000kg of harvest. Cost-Benefit results indicated that such a scenario would most likely generate AUD5.48 benefit for every AUD1.00 invested in releasing Eastern King Prawn. Achieving a benefit of less than AUD2.37 was extremely unlikely. This study indicates a favorable assessment of the potential economic benefits derived from a release of 3,000,000 Eastern King Prawns into Wallagoot Lake. Also, the simple approach presented provides a framework which may be useful for assessing other recreational fishery enhancement projects. Bioeconomic modelling is an important tool for understanding the potential benefits and risks of enhancement or sea ranching projects.

SU-G-201-02: Application of RayStretch in Clinical Cases: A Calculation for Heterogeneity Corrections in LDR Permanent I-125 Prostate Brachytherapy

Purpose: Tissue heterogeneities and calcifications have significant impact on the dosimetry of low energy brachytherapy (BT). RayStretch is an analytical algorithm developed in our institution to incorporate heterogeneity corrections in LDR prostate brachytherapy. The aim of this work is to study its application in clinical cases by comparing its predictions with the results obtained with TG-43 and Monte Carlo (MC) simulations. Methods: A clinical implant (71 I-125 seeds, 15 needles) from a real patient was considered. On this patient, different volumes with calcifications were considered. Its properties were evaluated in three ways by i) the Treatment planning system (TPS) (TG-43), ii) a MC study using the Penelope2009 code, and iii) RayStretch. To analyse the performance of RayStretch, calcifications located in the prostate lobules covering 11% of the total prostate volume and larger calcifications located in the lobules and underneath the urethra for a total occupied volume of 30% were considered. Three mass densities (1.05, 1.20, and 1.35 g/cm3) were explored for the calcifications. Therefore, 6 different scenarios ranging from small low density calcifications to large high density ones have been discussed. Results: DVH and D90 results given by RayStretch agree within 1% with the full MC simulations. Although no effort has been done to improve RayStretch numerical performance, its present implementation is able to evaluate a clinical implant in a few seconds to the same level of accuracy as a detailed MC calculation. Conclusion: RayStretch is a robust method for heterogeneity corrections in prostate BT supported on TG-43 data. Its compatibility with commercial TPSs and its high calculation speed makes it feasible for use in clinical settings for improving treatment quality. It will allow in a second phase of this project, its use during intraoperative ultrasound planning. This study was partly supported by a fellowship grant from the Spanish Ministry of Education, by the Generalitat Valenciana under Project PROMETEOII/2013/010, by the Spanish Government under Project No. FIS2013-42156 and by the European Commission within the SeventhFramework Program through ENTERVISION (grant agreement number 264552).

SU‐F‐T‐33: Air‐Kerma Strength and Dose Rate Constant by the Full Monte Carlo Simulations

Purpose:In general, the air‐kerma strength (Sk) has been determined by the energy weighting the photon energy fluence and the corresponding mass‐energy absorption coefficient or mass‐energy transfer coefficient. Kerma is an acronym for kinetic energy released per unit mass, defined as the sum of the initial kinetic energies of all the charged particles. Monte Carlo (MC) simulations can investigate the kinetic energy of the charged particles after photo interactions and sum the energy. The Sk of 192Ir source is obtained in the full MC simulation and finally the dose rate constant Λ is determine.Methods:MC simulations were performed using EGS5 with the microSelectron HDR v2 type of 192Ir source. The air‐kerma rate obtained to sum the electron kinetic energy after photoelectric absorption or Compton scattering for transverse‐axis distance from 1 to 120 cm with a 10 m diameter air phantom. Absorbed dose in water is simulated with a 30 cm diameter water phantom. The transport cut‐off energy is 10 keV and primary photons from the source need two hundred and forty billion in the air‐kerma rate and thirty billion in absorbed dose in water.Results:Sk is multiplied by the square of the distance in air‐kerma rate and determined by fitting a linear function. The result of Sk is (2.7039±0.0085)*10‐−11 µGy m2 Bq−1 s−1. Absorbed dose rate in water at 1 cm transverse‐axis distance D(r0, θ0) is (3.0114±0.0015)*10−11 cGy Bq−1 s−1.Conclusion:From the results, dose rate constant Λ of the microSelectron HDR v2 type of 192Ir source is (1.1137±0.0035) cGy h−1 U−1 by the full MC simulations. The consensus value conΛ is (1.109±0.012) cGy h−1 U−1. The result value is consistent with the consensus data conΛ.

Full Monte Carlo and measurement-based overall performance assessment of improved clinical implementation of eMC algorithm with emphasis on lower energy range

New version 13.6.23 of the electron Monte Carlo (eMC) algorithm in Varian Eclipse™ treatment planning system has a model for 4MeV electron beam and some general improvements for dose calculation. This study provides the first overall accuracy assessment of this algorithm against full Monte Carlo (MC) simulations for electron beams from 4MeV to 16MeV with most emphasis on the lower energy range. Beams in a homogeneous water phantom and clinical treatment plans were investigated including measurements in the water phantom. Two different material sets were used with full MC: (1) the one applied in the eMC algorithm and (2) the one included in the Eclipse™ for other algorithms. The results of clinical treatment plans were also compared to those of the older eMC version 11.0.31. In the water phantom the dose differences against the full MC were mostly less than 3% with distance-to-agreement (DTA) values within 2mm. Larger discrepancies were obtained in build-up regions, at depths near the maximum electron ranges and with small apertures. For the clinical treatment plans the overall dose differences were mostly within 3% or 2mm with the first material set. Larger differences were observed for a large 4MeV beam entering curved patient surface with extended SSD and also in regions of large dose gradients. Still the DTA values were within 3mm. The discrepancies between the eMC and the full MC were generally larger for the second material set. The version 11.0.31 performed always inferiorly, when compared to the 13.6.23.

On the use of MEIS cartography for the determination of Si1–xGex thin-film strain

The cartography from MEIS (Medium Energy Ion Scattering) is used to measure lattice deformation of strained Si1–xGex/Si heterogeneous epitaxial structures. Higher crystallographic index directions are shown to be specially sensitive to strain leading to a clear quantification of the strain with high sensitivity and accuracy. We provide a simple method to determine the lattice deformation and checked it against full Monte-Carlo simulations. Since MEIS has an excellent depth resolution it can be potentially used to quantify depth-dependent strain in thin-films as well as in nano-structured materials.