Primary Photons Research Articles

Quantitative Evaluation of Scintillation Camera Imaging Characteristics of Isotopes Used in Liver Radioembolization

BackgroundScintillation camera imaging is used for treatment planning and post-treatment dosimetry in liver radioembolization (RE). In yttrium-90 (90Y) RE, scintigraphic images of technetium-99m (99mTc) are used for treatment planning, while 90Y Bremsstrahlung images are used for post-treatment dosimetry. In holmium-166 (166Ho) RE, scintigraphic images of 166Ho can be used for both treatment planning and post-treatment dosimetry. The aim of this study is to quantitatively evaluate and compare the imaging characteristics of these three isotopes, in order that imaging protocols can be optimized and RE studies with varying isotopes can be compared.Methodology/Principal FindingsPhantom experiments were performed in line with NEMA guidelines to assess the spatial resolution, sensitivity, count rate linearity, and contrast recovery of 99mTc, 90Y and 166Ho. In addition, Monte Carlo simulations were performed to obtain detailed information about the history of detected photons. The results showed that the use of a broad energy window and the high-energy collimator gave optimal combination of sensitivity, spatial resolution, and primary photon fraction for 90Y Bremsstrahlung imaging, although differences with the medium-energy collimator were small. For 166Ho, the high-energy collimator also slightly outperformed the medium-energy collimator. In comparison with 99mTc, the image quality of both 90Y and 166Ho is degraded by a lower spatial resolution, a lower sensitivity, and larger scatter and collimator penetration fractions.Conclusions/SignificanceThe quantitative evaluation of the scintillation camera characteristics presented in this study helps to optimize acquisition parameters and supports future analysis of clinical comparisons between RE studies.

A GPU implementation of EGSnrc's Monte Carlo photon transport for imaging applications

EGSnrc is a well-known Monte Carlo simulation package for coupled electron–photon transport that is widely used in medical physics application. This paper proposes a parallel implementation of the photon transport mechanism of EGSnrc for graphics processing units (GPUs) using NVIDIA's Compute Unified Device Architecture (CUDA). The implementation is specifically designed for imaging applications in the diagnostic energy range and does not model electrons. No approximations or simplifications of the original EGSnrc code were made other than using single floating-point precision instead of double precision and a different random number generator. To avoid performance penalties due to the random nature of the Monte Carlo method, the simulation was divided into smaller steps that could easily be performed in a parallel fashion suitable for GPUs. Speedups of 20 to 40 times for 643 to 2563 voxels were observed while the accuracy of the simulation was preserved. A detailed analysis of the differences between the CUDA simulation and the original EGSnrc was conducted. The two simulations were found to produce equivalent results for scattered photons and an overall systematic deviation of less than 0.08% was observed for primary photons.

GRIPS - Gamma-Ray Imaging, Polarimetry and Spectroscopy

We propose to perform a continuously scanning all-sky survey from 200 keV to 80 MeV achieving a sensitivity which is better by a factor of 40 or more compared to the previous missions in this energy range. The Gamma-Ray Imaging, Polarimetry and Spectroscopy (GRIPS) mission addresses fundamental questions in ESA's Cosmic Vision plan. Among the major themes of the strategic plan, GRIPS has its focus on the evolving, violent Universe, exploring a unique energy window. We propose to investigate $\gamma$-ray bursts and blazars, the mechanisms behind supernova explosions, nucleosynthesis and spallation, the enigmatic origin of positrons in our Galaxy, and the nature of radiation processes and particle acceleration in extreme cosmic sources including pulsars and magnetars. The natural energy scale for these non-thermal processes is of the order of MeV. Although they can be partially and indirectly studied using other methods, only the proposed GRIPS measurements will provide direct access to their primary photons. GRIPS will be a driver for the study of transient sources in the era of neutrino and gravitational wave observatories such as IceCUBE and LISA, establishing a new type of diagnostics in relativistic and nuclear astrophysics. This will support extrapolations to investigate star formation, galaxy evolution, and black hole formation at high redshifts.

K-Shell Emission of Neutral Iron Line from Sagittarius B2 Excited by Subrelativistic Protons

Abstract We investigated the emission of the K$\alpha$ iron line from massive molecular clouds in the galactic center (GC). We assumed that at present the total flux of this emission consists of a time-variable component generated by primary X-ray photons ejected by Sagittarius A$^\ast$ (Sgr A$^\ast$) in the past, and a relatively weak quasi-stationary component excited by the impact of protons that were generated by star accretion onto the central black hole. The level of background emission was estimated from a rise of the 6.4 keV line intensity in the direction of several molecular clouds, which we interpreted as being a stage when the X-ray front ejected by Sgr A$^\ast$ entered into these clouds. Regarding the 6.4 keV emission before this intensity jump, we interpreted it as emission generated by subrelativistic cosmic rays there. The cross-section of K$\alpha$ vacancies produced by protons differs from that of electrons or X-rays. Therefore, we expect that this processes can be distinguished from an analysis of the equivalent width of the iron line; also, the time variations of the width can be predicted. The line intensity from the clouds depends on their distance from Sgr A$^\ast$ and the coefficient of spatial diffusion near the galactic center. We expect that in a few years the line intensity for the cloud G 0.11$-$0.11, which is relatively close to Sgr A$^\ast$, will decrease to a level of $\lesssim\ $10% from its present value. For the cloud Sagittarius B2 (Sgr B2) the situation is more intricate. If the diffusion coefficient is $D$$\gtrsim$ 10$^{27}\ $cm$^{2}\ $s$^{-1}$, the expected stationary flux should be about 10% of its level in 2000. In the opposite case the line intensity from Sgr B2 should drop down to zero because the protons do not reach the cloud.

A single scatter electron Monte Carlo approach for simulating gamma-ray stopping efficiencies of Geiger-Müller counters

Abstract In spite of their relatively poor gamma-ray stopping efficiencies, the Geiger-Muller (GM) counter is still preferred in many radioisotope gauges for industrial measurements. This is because these detectors exhibit a high degree of robustness in harsh environments, are relatively insensitive to temperature changes in the environment, and are inexpensive compared to other types of radiation detectors. These properties could make the use of GM counters very feasible in a number of industrial applications, such as gamma-ray tomography and gamma-ray density gauges, provided that their gamma-ray stopping efficiencies can be improved. The Monte Carlo (MC) method is a powerful computational physics tool that is utilized very often in the design of radiation detectors and radioisotope gauges. In this work a MC model for GM counters that is benchmarked with experiments at the primary photon energy of 59.5 keV is proposed. This is a specific purpose MC simulation code that, as opposed to publicly available general purpose MC codes, employs single scatter (or microscopic) electron transport and is currently under development. In this paper, the MC code is described in detail and the results of the specific purpose MC code are benchmarked with experiments and two general purpose MC codes, MCNP5 and PENELOPE. It was observed that the specific purpose MC code improved the reduced chi-square value when compared to MCNP5 and PENELOPE.

SU-E-T-100: Measurement of a Cobalt-60 Teletherapy Irradiator Spectrum Using a Compton Spectrometer

Purpose: To characterize the photon spectrum from a Theratronics T1000 cobalt-60 teletherapy unit using Compton spectrometry and compare to primary beam measurement and Monte Carlo (MC) simulation. Methods: A well-shielded high-purity germanium detector was used to measure the photon spectrum scattered at 22.5 and 70 degrees from the central axis of a 10cm×10cm beam of a cobalt-60 teletherapy unit. The central-axis photons were scattered using an aluminum rod (6mm diameter) positioned 100cm from the source, and the scattered photons were admitted to the detector through a 30cm-long collimating aperture (2mm diameter). The measured Compton-scattered spectra were corrected for detector response, determined using a model of the measurement apparatus in the MCNP5 MC code, and Compton relations (energy-angle and Klein-Nishina) to determine the central-axis spectrum at 100cm from the source. The primary photon spectrum was measured with the collimating aperture aligned to the central axis and corrected for detector response. A MC model of the cobalt-60 unit was developed in MCNP5 and used to generate the central-axis spectrum for a 10cmx10cm field. Results: The primary photon peaks from the cobalt-60 source were appropriately shifted to lower energies in the Compton-scattered spectra. The resolution of the shifted peaks degraded with increasing scattering angle. The corrected scattered spectra compared well with the primary measurement and MC simulation for peak position, but disagreed in the lower-energy continuum where source and collimator scatter are present. Differences are likely due to resolution loss with scattering and incomplete measurement correction. Conclusions: The spectrum from a cobalt-60 teletherapy unit was measured using Compton spectrometry. This spectrum was compared to direct measurement and MC simulation of the unit. Results indicate that small scattering angles should be used with this measurement technique and that further work is required to reconcile differences between measurements and simulations for source and collimator scatter.

SU‐E‐T‐334: A Rapid Method for Testing the Accuracy of Heterogeneity Correction Algorithms Using a 2‐D Detector‐Array QA Tool

Purpose: To demonstrate an efficient quality assurance (QA) method using a 2‐D diode array to verify the absolute dose distribution generated by heterogeneity corrected treatment plans. Methods: The AAA, ETAR, and modified Batho heterogeneity corrected Eclipse treatment plans were compared against the measured data obtained with 6 and 18MV (Varian 2100CD) photon irradiation with the following two geometric setups: (1) Reference setup: An inhomogeneous phantom was sandwiched by a solid water slab (Gammex) and the 22×22cm2 MapCHECK detector (Sun Nuclear) under the incident photon beam that was perpendicular to the slabs. The sandwiched slab material consisted of low‐density foam occupying half of the detector area (11×22cm2), and another solid‐water slab on the other half. (2) Tested setup: two blocks of solid‐water separated by another slab of low‐density foam were erected vertically on the surface of the 2‐D array. A slightly oblique beam angle (<30o) allows primary photon field to pass through each slab of solid water and foam to project the field onto the array. Results: The measured 2‐D dose profiles from the first configuration (Reference setup) were reasonably predicted by all three algorithms, but only AAA among the three taking into account the electron transport shows the best results for the second setup. Conclusions: The geometric design of the second setup with oblique beam angle can enhance the characteristics of the complicated dose profile projected onto a 2‐D array as the transversal and longitudinal electron transports carry out non‐local dose deposit throughout inhomogeneous slabs by oblique primary photons. The combination of build‐up and build‐down profiles is usually illustrated by film dosimetry with much a more time‐consuming procedure.

SU-E-J-15: A GPU-Based Monte Carlo Tool for Computing DRRs with Multiple Scattering

Purpose: To develop a GPU-based kV Monte Carlo (MC) simulation tool for computing CBCT x-ray projection images including both primary and scattered photon signals. Methods: We have developed a MC simulation code on GPU architecture using NVIDIAˈs CUDA API. Photon cross section data of various interaction types in the kV energy range are obtained from the PENELOPE database. The Woodcock transport technique is used for simulating photon transport without the need for voxel boundary crossing. Photon energy fluence at a detector location is recorded as the projection image. Multiple tallies are employed to record primary photon energy fluence (no scattering) and the fluences from photons undergoing first, second, and higher order scatters. To test our MC code, we simulated the geometry of a realistic Varian OBI system. We imaged a patientˈs head and an XCAT chest phantom with 10 billion source photons having a flat source fluence map collimated to a 40.0 cm by 30.0 cm detector. A mono-energetic x-ray source of 100.0 keV is used. Results: The computation time to simulate 10 billion photons for imaging both patientˈs head and the XCAT chest phantom was around 16 minutes on an NVidia C2050 GPU card. We found the total scattering signal to be approximately 10 percent of the primary signal in both cases. We also found that the total signal from higher order scattering is not negligible when imaging the XCAT chest phantom due to its large size and higher probability of scattering the photons.Conclusion: We successfully developed a Monte Carlo based kV imaging tool for simulating x-ray projections. X-ray projections obtained by this work will facilitate many research projects, where accurate x-ray projection images are needed, such as scatter removal in the CBCT reconstruction problem.

SU‐E‐I‐70: Characterisation of the Parameters Defining a Kilovoltage Source for Accurate Dose Computation

Purpose: To perform a sensitivity analysis of the parameters that define beam quality for a kilovoltage (kV) x‐ray sourceMethods: Using a previously developed hybrid approach to calculate radiation dose deposited by x‐ray beams of energies <150 kVp, we computed dose inside a simulated heterogeneous phantom for varying beam spectra to evaluate the sensitivity of calculated dose to half‐value layer (HVL). The approach involves computing the primary photon component deterministically and scattered component stochastically, accounting for the real micro cross sections of the materials involved. We characterized the spectrum of the Varian® On‐Board Imaging® units at our institution by HVL measurements made using of a Farmer‐type Capintec ion chamber (0.06cc) in air. We compared doses computed with our characterized source spectrum with measurements inside water‐equivalent Gammex® Solid Water® phantom. Measurements were done using a 10×10 cm2 field at 100 cm SSD at every centimeter for depths 1 to 12 cm. Results: We found that measuring kV and HVL gives us sufficient beam quality information for accurate [>0.5%] x‐ray dose calculations. We also showed that HVL varies by less than 0.1 mm Al for field sizes over 5×5 cm2, allowing us to use one HVL irrespective of field size. Agreement between calculations and experimental measurements was better than 2% for a transverse profile and the central axis depth dose. This implies that our approach to characterizing the beam quality of a kV source is suitable for ensuring accurate results Conclusions: We have determined the parameters we need to characterize the source in order to obtain good agreement between theoretical calculations and experimental measurements. This is a crucial step in developing an independent tool to calculate patient dose from kV beams such as cone‐beam CT and brings us closer to our goal of calculating patient‐specific dose from imaging procedures.

SU‐E‐T‐678: Monte Carlo Investigation on Dose Perturbations in the Lung Due to Constant Magnetic Fields during MRIgRT

Purpose: Magnetic resonance image‐guided radiotherapy (MR‐IGRT) has emerged as a promising new technology to reduce tumor position uncertainty during photon radiotherapy treatments of lung cancer. MRIGRT improves upon traditional IGRT techniques by providing real‐time intrafraction imaging of tumor motion. However, the use of MRI during beam delivery complicates treatment planning since the magnetic field will perturb the radiation dose distribution especially in fields prescribed in heterogeneous regions of the body such as the lung. In this study we used Monte Carlo methods to investigate the magnetic field effects on dose distributions near interfaces of high‐ and low‐density regions where the influence of magnetic fields will be significant. Methods: The Monte Carlo code EGS4nrc was used for all simulations performed in this study. We investigated dose distributions from both Co‐60 and 6‐MV photon beam energy spectra in simple heterogeneous phantoms. The phantoms consisted of alternating slabs of PMMA and air or lung material with different thicknesses. Homogeneous transverse magnetic fields of varying strengths were applied to the phantom during the simulations. Results: Large perturbations in the dose distributions near PMMA‐air or PMMA‐lung interfaces were recorded when a transverse magnetic field was applied to the phantom, which can be attributed to electron return effect. It was demonstrated that the size of the perturbation at an interface depends not only on the magnetic field strength, but also on the primary photon beam energy spectrum and the length of the air cavity within the phantom. Conclusions: Preliminary results demonstrated that magnetic fields alter the delivered dose distributions near interfaces of high‐ and low‐density regions. Therefore, accurate planning for MR‐IGRT treatments of lung cancer may need to consider magnetic field effects on the dose distribution. Future work will use Monte Carlo methods to investigate dose perturbations due to magnetic fields in 4D patient geometry.

MO-F-BRB-04: Multi-Source Modeling of Flattening Filter Free (FFF) Beam and the Optimization of Model Parameters

Purpose: To suggest a novel analytic beam source model for a flattening filter free(FFF) beam, a multi‐source model and its optimization method applicable to a treatment planning system were developed. Methods: Previous three source model was improved by introducing off axis ratio (OAR) of primary photon fluence to generate cone shape profiles. The parameters of the model and the OAR were determined from measured head scatter factors and a measured dose profile of a 40 × 40 cm2 field size using a line search optimization technique. A new method to acquire gradient terms for OAR's was developed to enhance the speed of the optimization process. The improved model was validated with measured dose profiles from 3 × 3 cm2 to 40 × 40 cm2 field sizes at 6 and 10 MV from a TrueBeamTM STx linear accelerator. Furthermore, planar dose distributions for clinically used radiation fields were also calculated and compared with measurements using a 2D array detector using the gamma index method. Results: All dose values for the calculated profiles agreed with the measured dose profiles within 0.5% at 6 and 10 MV beams, except for some low dose regions for larger field sizes. A slight overestimation was seen in the lower penumbra region near the field edge for the large field sizes by 1 % ∼ 4%. The planar dose calculations showed comparable passing rates (> 98%) when the criterion of the gamma index method was selected to be 3%/3 mm. Conclusions: Developed source model showed good agreements between measured and calculated dose distributions. The model is easily applicable to any other linear accelerator using FFF beams as the data required include only the measured PDD, dose profiles and output factors for various field sizes, which are easily acquired during conventional beam commissioning process.

MO‐F‐110‐04: Experimental Validation of a Novel Approach to Fast and Accurate Kilovoltage Dose Computation

Purpose:To validate a novel hybrid method for the calculation of kilovoltage (kV) x‐ray dose. Methods: We performed experimental validation of a novel hybrid approach for calculating dose deposited by imaging beams (<150 kVp). The approach involves computing the primary photon component deterministically and scattered component stochastically, accounting for the real micro cross sections of the materials involved. Depth dose and profile measurements for the Varian® On‐Board Imaging® unit in the radiographic mode using a 125 kVp x‐ray beam (4.6 mm Al half‐value layer) were performed. The measurements were made using a Farmer‐type Capintec ion chamber (0.06cc) in homogeneous and heterogeneous phantoms. A phantom consisting of Certified Therapy‐Grade Solid Water® (Gammex 457) was used to measure the dose under homogeneous conditions. The heterogeneous phantom was constructed using lung‐ equivalent material (Gammex 455) and bone‐equivalent material (Gammex 450). Results: Measurements in the homogeneous phantom agreed with theoretical calculations within 2% for depth doses and within 2% of the central axis dose for profiles. Local agreement in highly attenuated regions such as depths >10 cm or outside the beam edge were about 10%. However, the dose differences in these regions were less than 2% of the maximum dose. Conclusions: This work provides experimental validation of our hybrid calculation method. The next step will be to test the algorithm using more complex phantoms, such as the anthropomorphic Rando® phantom, which mimics patient geometry as well as inhomogeneities. This is a crucial step in the validation of an independent tool to calculate patient dose from kV beams such as cone‐beam CT and brings us closer to our goal of calculating patient‐specific dose from imaging procedures.

SU-E-T-219: Ion Chamber Dosimetry Modification under Strong Magnetic Field Conditions; Air and Liquid Filled Chambers Study

Purpose: To examine the dose response of ion chambers in an external high magnetic field,conductingmeasurements and Monte Carlo simulations. To examine a liquid filled ion chamber (LION) as a low B field dependant on‐time dosimeter. Methods: This work investigates the response of a 0.6cm3 Farmer chamber to a 11.17 mCi 137Cs source under the influence of a 1.5 T magnetic field. A special setup allowed measurements for transverse and longitudinal field directions inside a 1.5T MRI bore. Monte Carlo simulations were conducted using FLUKA, a particle physics transport package. A PTW 0.002 cm3 MicroLion chamber is offered as a non‐correctional on‐line B field measurement alternative, since it introduces a small cavity and no air phantom voids. Results: Higher Farmer chamber currents were obtained when a transverse (to chamber central axis) magnetic field was applied, compared to zero B field conditions. Lower readings were obtained when a longitudinal field was present. Measurements have shown that the electric field between the electrodes has a very small impact on the ion collection, and can be neglected for simulation purposes. A microLion chamber was found not to have response impact due to the presence of a magnetic field. Conclusions: The dose response of a Farmer chamber in an external magnetic field varies with the average charged particle trajectory length. The average trajectory depends on the B field magnitude and direction, and on the energy spectrum of the primary photon beam. Thus, an alignment with the B field direction would be essential. A liquid‐filled chamber is offered as an alternative due to its homogeneous structure and small cavity that results in no B field correction needed.

MO-F-BRB-01: Convolution Based Dose Calculation in Microbeam Radiation Therapy

Purpose: Microbeam Radiation Therapy(MRT) uses synchrotron keV x‐ray sources. So far dose calculations in MRT are based on time consuming Monte Carlo(MC) simulations. We have developed convolution based methods to calculate dose in MRT employing theoretically motivated kernels. Methods: Whereas the Compton effect is the only dominant effect in the MeV x‐ray range, the photoelectric effect becomes more important at lower energy (E<150keV) rendering simple electron density scaling impossible. Furthermore photon scattering becomes more important, whereas electrons are absorbed locally. We have split energy absorption into scattering orders according to the number of preceding Compton events. With some reasonable approximations of the scattering cross sections, spatial energy distributions can be derived analytically in different scattering orders. From this we derive rules to scale kernels in different materials. The microbeam profile is produced by electrons created in primary photon interactions that have a range of less than 300μm. We also simplified electron scattering in order to predict beam penumbras. Results: Comparisons with MC simulations at different energies show good agreement. Differences for broad field irradiation of homogeneous material are less than 1% along the beam axis and less than 20% inside a 100mm radius. Simulations of bone in water show differences of up to 12% close to interfaces. Application of the methods to a real head CT also showed good agreement. Due to the integrating character of the method structures in the scattereddose cannot be resolved. The microbeam profile is well resolved and agreement in the valley region is better than 5%. Conclusions: The developed methods reduce dose calculation times in MRT down to a few minutes and make parameter optimisation and treatment planning possible. However, the accuracy cannot compete with MC simulations, but this seems not to be a big compromise considering biological uncertainties.

Low-energy photons in high-energy photon fields – Monte Carlo generated spectra and a new descriptive parameter

The varying low-energy contribution to the photon spectra at points within and around radiotherapy photon fields is associated with variations in the responses of non-water equivalent dosimeters and in the water-to-material dose conversion factors for tissues such as the red bone marrow. In addition, the presence of low-energy photons in the photon spectrum enhances the RBE in general and in particular for the induction of second malignancies. The present study discusses the general rules valid for the low-energy spectral component of radiotherapeutic photon beams at points within and in the periphery of the treatment field, taking as an example the Siemens Primus linear accelerator at 6 MV and 15 MV. The photon spectra at these points and their typical variations due to the target system, attenuation, single and multiple Compton scattering, are described by the Monte Carlo method, using the code BEAMnrc/EGSnrc. A survey of the role of low energy photons in the spectra within and around radiotherapy fields is presented. In addition to the spectra, some data compression has proven useful to support the overview of the behaviour of the low-energy component. A characteristic indicator of the presence of low-energy photons is the dose fraction attributable to photons with energies not exceeding 200 keV, termed P D 200keV . Its values are calculated for different depths and lateral positions within a water phantom. For a pencil beam of 6 or 15 MV primary photons in water, the radial distribution of P D 200keV is bellshaped, with a wide-ranging exponential tail of half value 6 to 7 cm. The P D 200keV value obtained on the central axis of a photon field shows an approximately proportional increase with field size. Out-of-field P D 200keV values are up to an order of magnitude higher than on the central axis for the same irradiation depth. The 2D pattern of P D 200keV for a radiotherapy field visualizes the regions, e.g. at the field margin, where changes of detector responses and dose conversion factors, as well as increases of the RBE have to be anticipated. Parameter P D 200keV can also be used as a guidance supporting the selection of a calibration geometry suitable for radiation dosimeters to be used in small radiation fields.

Extreme TeV blazars and the intergalactic magnetic field

We study the four BL Lac objects (RGB J0152+017, 1ES 0229+200, 1ES 0347-121 and PKS 0548-322) detected in the TeV band but not present in the 1FGL catalogue of the Fermi/Large Area Telescope. We analize the 24 months of LAT data deriving gamma-ray fluxes or upper limits that we use to assemble their spectral energy distributions (SED). We model the SEDs with a standard one-zone leptonic model, also including the contribution of the reprocessed radiation in the multi GeV band, emitted by the pairs produced through the conversion of the primary TeV emission by interaction with the cosmic optical-IR background. For simplicity, in the calculation of this component we adopt an analytical approach including some simplifying assumptions, in particular i) the blazar high energy emission is considered on average stable over times of the order of 10^7 years and ii) the observer is exactly on-axis. We compare the physical parameters derived by the emission model with those of other high-energy emitting BL Lacs, confirming that TeV BL Lacs with a rather small GeV flux are characterized by extremely low values of the magnetic field and large values of the electron energies. The comparison between the flux in the GeV band and that expected from the reprocessed TeV emission allows us to confirm and strengthen the lower limit of B >10^{-15} G for the intergalactic magnetic field using a theoretically motivated spectrum for the primary high-energy photons.

Epp: A C++ EGSnrc user code for x‐ray imaging and scattering simulations

Easy particle propagation (Epp) is a user code for the EGSnrc code package based on the c+ + class library egspp. A main feature of egspp (and Epp) is the ability to use analytical objects to construct simulation geometries. The authors developed Epp to facilitate the simulation of x-ray imaging geometries, especially in the case of scatter studies. While direct use of egspp requires knowledge of c+ +, Epp requires no programming experience. Epp's features include calculation of dose deposited in a voxelized phantom and photon propagation to a user-defined imaging plane. Projection images of primary, single Rayleigh scattered, single Compton scattered, and multiple scattered photons may be generated. Epp input files can be nested, allowing for the construction of complex simulation geometries from more basic components. To demonstrate the imaging features of Epp, the authors simulate 38 keV x rays from a point source propagating through a water cylinder 12 cm in diameter, using both analytical and voxelized representations of the cylinder. The simulation generates projection images of primary and scattered photons at a user-defined imaging plane. The authors also simulate dose scoring in the voxelized version of the phantom in both Epp and DOSXYZnrc and examine the accuracy of Epp using the Kawrakow-Fippel test. The results of the imaging simulations with Epp using voxelized and analytical descriptions of the water cylinder agree within 1%. The results of the Kawrakow-Fippel test suggest good agreement between Epp and DOSXYZnrc. Epp provides the user with useful features, including the ability to build complex geometries from simpler ones and the ability to generate images of scattered and primary photons. There is no inherent computational time saving arising from Epp, except for those arising from egspp's ability to use analytical representations of simulation geometries. Epp agrees with DOSXYZnrc in dose calculation, since they are both based on the well-validated standard EGSnrc radiation transport physics model.

Search for primary photons and neutrinos in the ultra-high energy cosmic rays with the Pierre Auger Observatory

Along with primary protons and nuclei most of the scenarios of the origin of cosmic rays predict fluxes of photons and neutrinos at the highest energies. Thanks to the huge collection area and the hybrid design, combining ground array and fluorescence detection techniques, the Pierre Auger Observatory is a unique tool to search for primary photons and neutrinos in ultra-high energy cosmic rays. Implications of these searches extend from astrophysics to fundamental and particle physics. Current results and future perspectives are reported.

Extremity dosimetry problems during the handling of radionuclides syringes in nuclear medicine: A Monte Carlo radiation transport simplified approach

Abstract The ORAMED (Optimization of RAdiation protection for MEDical staff) Working Tasks (WP4) is addressed at evaluating extremity doses (and dose distributions across the hands) of medical staff working in nuclear medicine departments, to study the influence of protective devices such as syringe and vial shields, to improve such devices when possible and to propose “levels of reference doses” for each standard nuclear medicine procedure. In particular task 4 is concerned with the study of the extremity dosimetry for the hand of operators devoted to the preparation and administration stages of the usage, for example, of 99mTc, 18F and 90Y (Zevalin) radionuclides. The aim of this report consists in the study of photon-electron equilibrium conditions at 0.07 mm in the skin to justify a simplified “kerma approximation” approach in the planned complex Monte Carlo voxel hand modeling. Furthermore a detailed investigation on primary electron and secondary bremsstrahlung photon transport from 90Y to speed up the calculations was performed. The results obtained in the simplified investigated conditions could be of help for the production calculations, introducing, if necessary, suited correction factors applicable to the complex condition results.

A 1st generation scatter CT algorithm for electron density breast imaging which accounts for bound incoherent, coherent and multiple scatter: A Monte Carlo study.

Breast CT is an emerging modality that reconstructs 3D linear attenuation coefficient (μ) images of the breast. Its tomographic nature reduces the overlap of structures and may improve tissue visualization. Current prototype systems produce large levels of scatter that could be used to reconstruct electron density (ρ<formula> _{e}</formula>) images. This could potentially enhance diagnosis. We are developing a first generation bench top CT system to investigate the benefits of simultaneous imaging μ and ρ<formula> _{e}</formula> of the intact breast. The system uses an algorithm capable of reconstructing ρ <formula>_{e}</formula> images from single Klein-Nishina scatter. It has been suggested that this algorithm may be impractical since measurements include coherent, bound incoherent and multiple scatter. To investigate this, the EGSnrc Monte Carlo (MC) code was used to simulate scans using a first generation system. These simulations were used to quantify the dose per scan, to provide raw data for the ρ<formula> _{e}</formula> reconstructions and to investigate corrections for multiple and coherent scatter since these can not be directly related to ρ<formula> _{e}</formula>. MC simulations show that the dose coefficients are similar to those of cone beam breast CT. Coherent scatter is only ∼9% concentrated in scattering angles < 8°. Electron binding reduces the number of incoherently scattered photons but this reduction can be included in the quantification of scatter measured by the system. Multiple scatter was found to be the major source of errors and, if not corrected for, can result in an overestimation of ρ<formula> _{e}</formula> by more than a factor of two. Empirical corrections, based on breast thickness or radiological path, can be used to reconstruct images where the variance in ρ<formula> _{e}</formula> error is half of that found in images derived from primary photons only. Although some practical challenges remain in creating a laboratory system, this work has shown that it is possible to reconstruct scatter images of the breast with a 4 mGy dose and further experimental evaluation of this technique is warranted.