PMMA Thicknesses Research Articles

'Dirty dose'-based proton variable RBE models - performance assessment on in vitro data.

In clinical proton radiotherapy, a constant relative biological effectiveness (RBE) of 1.1 is typically applied. Due to abundant evidence of variable RBE effects from in vitro data, multiple variable RBE models have been suggested, typically by describing the and parameters in the linear quadratic (LQ) model as a function of dose averaged linear energy transfer ( ). This work introduces a new variable RBE model based on the dirty dose concept, where dose deposited in voxels with a corresponding LET exceeding a specific threshold is considered "dirty" in the sense that it has a biological effect above the one predicted by a constant RBE of 1.1. As only one LET level, corresponding to a specific energy for a given particle in a given medium, needs to be monitored, this offers several advantages, such as simplified calculations by removing the need for intricate end of range LET calculations and averaging procedures, as well as opening up for more efficient experimental assessment of the cell specific modelparameters. Previously published in vitro data were utilized, where surviving fraction (SF), dose and were reported for a pristine proton beam with varying physical PMMA thicknesses placed upstream of the cells. The setup was re-simulated to extract dirty dose metrics for the corresponding reported -values. Models were created by setting the parameter of the LQ model as a function of the fraction of dirty dose and subsequently benchmarked against models based on other radiation quality metrics by comparing the root-mean-square-error (RMSE) of the predicted and actual cell survivingfraction. Variable RBE models based on dirty dose perform on par with conventional radiation quality metrics with a RMSE of 0.38 for a dirty dose-based model with a threshold of 7 , compared to 0.42 and 0.36 for a -based and -based model, respectively. Higher chosen LET thresholds typically performed better and lower performedworse. The results indicate that models based on dirty dose metrics perform equally well as conventional radiation quality metrics. Due to the simplified calculations involved and the potential for more efficient measurement techniques for data generation, dirty dose-based models might be the most conservative and practical approach for creating future proton variable RBEmodels.

Physical and dosimetric characterisation of different Contrast-Enhanced digital mammographic systems: A multicentric study

PurposeContrast-enhanced digital mammography (CEDM) is a relatively new imaging technique recombining low- and high-energy mammograms to emphasise iodine contrast. This work aims to perform a multicentric physical and dosimetric characterisation of four state-of-the-art CEDM systems. MethodsWe evaluated tube output, half-value-layer (HVL) for low- and high-energy and average glandular dose (AGD) in a wide range of equivalent breast thicknesses. CIRS phantom 022 was used to estimate the overall performance of a CEDM examination in the subtracted image in terms of the iodine difference signal (S). To calculate dosimetric impact of CEDM examination, we collected 4542 acquisitions on patients. ResultsEven if CEDM acquisition strategies differ, all the systems presented a linear behaviour between S and iodine concentration. The curve fit slopes expressed in PV/mg/cm2 were in the range [92–97] for Fujifilm, [31–32] for GE Healthcare, [35–36] for Hologic, and [114–130] for IMS. Dosimetric data from patients were matched with AGD values calculated using equivalent PMMA thicknesses. Fujifilm exhibited the lowest values, while GE Healthcare showed the highest. ConclusionThe subtracted image showed the ability of all the systems to give important information about the linearity of the signal with the iodine concentrations. All the patient-collected doses were under the AGD EUREF 2D Acceptable limit, except for patients with thicknesses ≤35 mm belonging to GE Healthcare and Hologic, which were slightly over. This work demonstrates the importance of testing each CEDM system to know how it performs regarding dose and the relationship between PV and iodine concentration.

Improving input contrast estimation to an x-ray imaging system

Objective. An appropriate parameter to study the performance of an x-ray imaging system is contrast transfer, or the system’s ability to capture contrast in the radiation beam and bring it to the image. However, determining the input contrast to the system is difficult, as it is heavily affected by secondary radiation, which in turn depends on a multitude of factors. This work presents a method to improve the calculation of input contrast to the imaging system when PMMA phantoms are used. Approach. An expression to obtain input contrast from primary radiation attenuation and scatter-to-primary ratio is shown, and the approximation upon which it is based is discussed. Primary and secondary radiation emerging from the phantoms are calculated for monoenergetic pencil beams impinging on planar PMMA phantoms of different thicknesses. Monte Carlo simulations of two types of anti-scatter grids are also incorporated into the calculations. Main results. The primary and secondary components of radiant energy and grid transmission factors are presented for monoenergetic beams with energies from 10 to 150 keV. These results are then used to calculate input contrast for polyenergetic beams when using a commercial image quality phantom combined with different thicknesses of PMMA and anti-scatter grids. Significance. The information of the object contrast carried by the beam constitutes the input to the imaging system. An accurate determination of this input contrast can be carried out in a wide variety of situations from the study of a reduced number of cases, as those presented in this work for monoenergetic beams, PMMA phantoms of different thicknesses and anti-scatter grids. The relationship between the input contrast and the contrast due to primary radiation used in this work provides a good approximation for the different combinations of inserts, phantoms, grids, and energy spectra analyzed here.

Adhesion Behavior of Ti\u2013PMMA\u2013Ti Sandwiches for Biomedical Applications

The “stress-shielding” problem, common with metallic implants, may be solved by using biocompatible sandwiches with a polymeric core between two metallic skin sheets. To achieve such sandwiches, a process route has been developed, beginning with the grafting of poly-(methyl-methacrylate) (PMMA) on titanium (Ti) sheets via the “grafting from” technique. Grafting resulted in variable thicknesses of PMMA on the Ti sheets. Hot-pressing was used to prepare semi-finished Ti–PMMA–Ti sandwiches. The adhesion was achieved by the interpenetration between PMMA sheet and the grafted PMMA chains. Investigation was carried out to understand the influence of the grafted PMMA thickness on the adhesion strength. Similar adhesion strengths were found for the sandwiches despite variable grafted PMMA thicknesses, indicating a successful grafting of PMMA on large-scale Ti sheets. The adhesion followed the autohesion theory, where a time-dependent increase in adhesion strength was found for the sandwiches.

Do carers and comforters require lead aprons during general radiographic examinations?

Carers and comforters frequently remain with children during paediatric general radiographic examinations. As well as improving the likelihood of overall success of the procedure, this can be important for minimising stress and anxiety of the child. Wearing lead aprons can contribute to additional stress and anxiety about the procedure for both carer and child, specifically due to radiation risk. It also introduces some practical challenges for radiographers. This study quantified a carers exposure to scattered radiation for general radiographic examinations when remaining with a child to assist in positioning or to comfort them. Scattered radiation was measured at four common locations where a carer may stand, with a range of tube potentials (40 kVp to 100 kVp ) and PMMA thicknesses of 2.5-22.5 cm. This was then matched to our clinical protocols to estimate the radiation dose a carer could be exposed to while assisting a patient during general radiographic examinations. The effective dose received by a carer standing 20 cm from the centre of the patient varies from 11 min of Australian natural BERT for a finger radiograph on a patient <3 kg and up to 62 h for a swimmers view radiograph performed on a patient >70 kg. This dosimetric data allowed an evidence-based assessment of radiation protection requirements for the carer using the ALARA principle. At our institution, it was decided that a lead apron is not required if the carer is unlikely to receive more than 2 µSv. A new policy, presented here, was developed to implement this decision.

Helium ion beam lithography and liftoff

We introduce a helium ion beam lithography and liftoff process to fabricate arbitrary nanostructures. Exploiting existing high-resolution positive tone resists such as poly (methyl methacrylate) (PMMA), the process offers three significant advantages over electron beam lithography: (a) the exposing helium ion beam produces a high secondary electron yield leading to fast patterning, (b) proximity effects are negligible due to the low count of backscattered helium ions from the substrate, and (c) the process is transferrable with minimal alteration among different types of substrates (e.g. silicon, fused silica). The process can be used to pattern any material compatible with liftoff such as evaporated metals or dielectrics, and allows overlay of nanostructures precision-aligned to microstructures realised beforehand on the same substrate. The process is demonstrated for several PMMA thicknesses to liftoff different thicknesses of deposited material. Resolution trials are conducted to determine the limits of the process for each PMMA thickness. Isolated lines as narrow as 14 nm, and line-space gratings of 40 nm pitch (50% duty cycle), are produced as resolution tests by lifting off a 20 nm thick Au film. Nanostructures of aspect ratio up to ∼3:1 have been realised. Plasmonic nanoantenna arrays overlaid to microscale contacts are produced as device demonstrators, for which optical measurements are in excellent agreement with theory.

Characterization of the Detonation Pressure of a PETN Based PBX with the Optical Active Method

AbstractDetonation metrology is essential for the development of energetic materials, to characterize existing explosives, and to characterize materials behavior under high pressures. The optical active method (OAM), based on PMMA optical fibers (250 μm diameter) and their radiation transmission loss when shocked, was used to characterize the detonation wave (DW) and shock wave (SW) in inert barriers and applied to measure the detonation pressure in condensed explosives. The detonation velocity and detonation pressure of a PBX based on PETN (86 % PETN, 14 % Sylgard), known as Seismoplast were measured. The OAM with protected optical probes (POP) was used to determine the mean detonation velocity (7337 m s−1), whereas the OAM with bare optical probes (BOP) was used to measure the induced shock velocities generated by Seismoplast on different thicknesses of PMMA (1–9 mm), aluminum and copper (1–7 mm). Based on the shock velocities at the interfaces between the explosive and the inert barriers, the CJ pressure of Seismoplast was determined as 21.2 GPa.

Position-Dependent Diffusion Dynamics of Entangled Polymer Melts Nanoconfined by Parallel Immiscible Polymer Films.

The morphological structure and dynamics of confined polymers adjacent to the polymer-polymer interface have a profound effect on determining the overall physical properties of polymer blends. We measured the diffusion dynamics of poly(methyl methacrylate) (PMMA) melts confined between polystyrene (PS) layers using neutron reflectivity. Combinations of various thicknesses of PMMA and deuterated PMMA (dPMMA) allowed us to experimentally reveal the nonmonotonic behavior of polymer mobility near the PS-PMMA interface. From the neutron reflectivity results, we found that the polymers adjacent to the immiscible polymer-polymer interface showed enhanced diffusion dynamics because of the repulsive interaction between PS and PMMA, whereas the polymer at local regions farther from the interface exhibited reduced dynamics. This is probably due to the nonspherical conformation of PMMA and spatial confinement near the PS-PMMA interface.

105. Upgrading Philips Allura Xper FD20 angiography system to Allura Clarity: Analysis of dose reduction and image quality

Purpose Our Allura Xper FD20 system was installed in 2013 and mainly used for stroke treatment. To reduce the radiation dose delivered to patients though maintaining the required image quality, the system was recently upgraded to Allura Clarity. The core characteristics of Allura Clarity family are new real-time image processing algorithms to reduce image noise. The aim of this work is to show the advantages obtained in terms of dose reduction for cardiac, vascular and electrophysiological studies following such upgrade. Methods For both angiographic systems, the patient dose was assessed by means of K a,e (Entrance Air Kerma) measurements, using a PMMA phantom to simulate patient attenuation. The measurement set up was the referred method indicated in the RP162 report [1] and extensively described by Martin [2] . For each investigated procedure, the measurements were carried out for most selectable fields of view and different PMMA thicknesses. The image quality was evaluated using Leeds TOR 18FG and FluoroMesh phantom for low contrast resolution and spatial resolution respectively. Results Depending on the procedure, the dose reduction is meaningful and ranges from 20% up to a factor of around 4 for fluorographic acquisitions. All K a,e values measured on Allura Clarity system are compliant with the Suspension Levels set out in the RP162 report [1] also for digital fluorographic acquisition mode. The image quality obtained with Allura Clarity is equivalent to that of the previous system. Conclusions The Allura Clarity delivers much lower dose to the patient for all clinical applications while maintaining an equivalent image quality.

Reducing the risk of skin injuries in cardiac catheterization procedures: Optimization proposal for obese patients

PurposeDuring interventional cardiology procedures, high doses of X-ray may be delivered to patients. This is especially critical in cases of obese patients and/or high obliquity projections. High dose rates can then be produced in patients’ skin as well as insufficient image quality due to regulatory limitations in the X-ray tube output working in the fluoroscopy mode. In this paper, an optimization action is proposed to reduce patient entrance dose rate and preserve image quality in cases of thick patients. MethodsThe action is based on the evaluation of dose rate to the patient and image quality in a new fluoroscopy protocol with less frame rate (7.5 vs. 15 frames/s) and higher spectral shape filter (0.4 vs. 0.1 mm Cu). The new protocol is tested in an angiography room using a PMMA phantom and a test object. ResultsThe new fluoroscopy protocol (7.5 fr/s and 0.4 mm Cu) reduces entrance surface air kerma in 70%–10% (depending on PMMA thickness), preserving the incident air kerma per frame at the image detector. While at lower PMMA thickness, the MTF measured with bar pattern is better for the default protocol; at PMMA thickness between 32 and 37 cm, the optimized protocol produces better image quality indicators. ConclusionsThis work demonstrates that in the case of high thicknesses of PMMA (32–37 cm), increasing spectral beam filter and reducing frame rate may help improve image quality and maintain entrance surface air kerma so as to fulfil the regulatory requirements.

Evaluation of patient dose saving in grid-less x-ray mammography acquisition compared with full field digital mammography (FFDMG) acquisition

Purpose. To investigate the patient radiation dose saving of grid-less x-ray mammography acquisitions compared with conventional full-field digital mammography (FFDMG). Methods and materials. The Siemens Inspiration MAMMOMAT PRIME system with software based scatter correction was used to investigate the dose saving in grid-less acquisition compared with conventional full-field digital mammography (FFDMG) acquisitions. A Piranha 657 solid-state detector was used to measure the entrance exposure. The entrance exposure was directly measured on different PMMA thicknesses of 20–70 mm in steps of 10 mm. The PMMA block thicknesses were then converted to an equivalent compressed breast tissue thicknesses. The average glandular dose (AGD) is calculated. Results. Dose reduction in both the directly measured entrance exposure and the calculated AGD is between 13% and 32% in the grid-less mammography acquisition. The contrast to noise ratio calculated in the grid-less and the FFDMG acquisition also was the same. Conclusion. It was possible to save patient dose (13%–32%) in grid-less mammography acquisition without affecting the image quality.

Wafer‐Scale Selective‐Area Deposition of Nanoscale Metal Oxide Features Using Vapor Saturation into Patterned Poly(methyl methacrylate) Templates

Adv. Mater. Interfaces. 2016, 3, 1500431 Figure 4 in this manuscript was published missing a label. The corrected version is below. In addition, two units in Experimental Section Polymer Patterning were published incorrectly. The corrected paragraph is below. Polymer Patterning: Patterning was accomplished using a Raith 150TWO electron beam lithography system. Test samples were used to determine proper dosing times for varying thicknesses of PMMA. For example, 200 nm PMMA was patterned with an area dose of 180 uC cm–2 and a line dose of 900 pC. Patterns were developed in 1:3 isopropyl alcohol: methyl isobutyl ketone (Acros) for 55 s and then isopropyl alcohol alone for additional 30 s. PMMA acts as a positive photoresist where the areas exposed to the electron beam are removed. The Raith system is available through North Carolina State University's Nanofabrication Facility and was used to pattern PMMA features as small as 30 nm. The authors apologise for any inconvenience caused by this oversight.

Assessment of dosimetric parameters in mammography employing a homemade ionization chamber

X-ray mammography examination is the reference tool to discover breast cancer in an early stage. The mammography unit must follow an accurate quality control program that covers both patient and staff radiation protection. Plane parallel ionization chambers are the reference instrument for dosimetry in mammography beams, but they can represent higher cost for small clinics in countries as Brazil. In this work, it is presented a low cost ionization chamber for mammography X-rays energy range dosimetry developed at IPEN. The homemade ionization chamber has a sensitive volume of 6.0 cm3 and it was utilized to execute quality control tests in two distinct mammography systems: a GE Senographe DMR-plus and a Philips VMI Graph Mammo. The setups for the tests performed agreed with the IAEA HHS 2 and 17 recommendations. A breast phantom of various PMMA thicknesses was utilized in this work. The homemade ionization chamber performance was compared to that of a commercial one. The maximum difference between the incident air kerma measured with the reference ionization chamber and the developed one was only 5.62% for the GE equipment and only 4.42% for the Philips equipment. The homemade ionization chamber presented an excellent performance in incident air kerma and HVL measurements for the radiographic techniques utilized in the present work. All the results obtained were within IAEA specifications.

P6. Digital breast tomosynthesis: Dose and image quality assessment

Introduction Digital Breast Tomosynthesis (DBT) offers a gain in sensitivity and in specificity for the detection of breast cancers compared to 2D mammography, due to reduction of the tissues’ overlapping. DBT is already used in many centers in France. The introduction of this technique within the French breast cancer screening program is being considered by the authorities for the coming years. As it has been done for 2D digital mammography, a protocol for quality control must be developed specifically for this technic. It is therefore necessary to increase our knowledge of tomosynthesis systems and of Image quality phantoms proposed by manufacturers. The aim of the study is to compare different DBT systems in term of dose and image quality. The evaluation of different image quality phantoms could lead to recommendations for internal quality control (regulatory or not). Methods Five French hospitals with three different tomosynthesis systems and seven specific phantoms have been included in the study. Average Glandular Dose and Signal Difference to Noise Ratio are assessed for different thicknesses of PMMA. Regarding image quality, reconstructed images are analyzed on global score, spatial resolution, geometrical distortion and homogeneity aspects. Results Preliminary results on dose and image quality for different models and different acquisition modes will be presented. Phantoms’ sensitivity at different dose levels will be discussed as well. Conclusions The variety of DBT systems design leads to an expected variability in terms of image quality and dose with breast thickness. Particular attention should be paid to the increased dose in comparison with 2D digital mammography. Works at a national level on the regulatory quality control of tomosynthesis systems should be initiated as soon as possible. The results of this study are expected to contribute to the national discussion on this topic.

Digital Breast Tomosynthesis: Dose and image quality characterization

Introduction Digital Breast Tomosynthesis (DBT) offers a gain in sensitivity and in specificity for detection of breast cancers compared to 2D mammography, due to tissues’ overlapping reduction. The introduction of this technique within the French breast cancer screening program is being considered by the authorities in the coming years. Purpose The aim of the study is to compare different DBT systems in term of dose and image quality. The evaluation of different image quality phantoms could lead to recommendations for incoming French regulatory internal quality control. Materials and methods Five French hospitals with three different tomosynthesis systems and seven specific phantoms have been included in the study. Average Glandular Dose and SDNR are assessed for different thicknesses of PMMA. Regarding image quality, reconstructed images are analyzed on global score, spatial resolution, geometrical distortion and homogeneity aspects. Results Preliminary results on dose and image quality for different models and modes are expected in May 2016 and will be discussed, as well as image quality and phantoms’ sensibility at different dose levels. Conclusion The diversity in design of Digital Breast Tomosynthesis systems leads to an expected variability in terms of image quality and dose with breast thickness. Particular attention should be paid to the increase of the dose. Work at a national level on the regulatory quality control of tomosynthesis systems should be initiated as soon as possible in France. Disclosure FITTON I: co-inventor of Tomomam® phantom.

Dosimetry and image quality in digital mammography facilities in the State of Minas Gerais, Brazil

Abstract According to the National Register of Health Care Facilities (CNES), there are approximately 477 mammography systems operating in the state of Minas Gerais, Brazil, of which an estimated 200 are digital apparatus using mainly computerized radiography (CR) or direct radiography (DR) systems. Mammography is irreplaceable in the diagnosis and early detection of breast cancer, the leading cause of cancer death among women worldwide. A high standard of image quality alongside smaller doses and optimization of procedures are essential if early detection is to occur. This study aimed to determine dosimetry and image quality in 68 mammography services in Minas Gerais using CR or DR systems. The data of this study were collected between the years of 2011 and 2013. The contrast-to-noise ratio proved to be a critical point in the image production chain in digital systems, since 90% of services were not compliant in this regard, mainly for larger PMMA thicknesses (60 and 70 mm). Regarding the image noise, only 31% of these were compliant. The average glandular dose found is of concern, since more than half of the services presented doses above acceptable limits. Therefore, despite the potential benefits of using CR and DR systems, the employment of this technology has to be revised and optimized to achieve better quality image and reduce radiation dose as much as possible.

Getting started with protocol for quality assurance of digital mammography in the clinical centre of Montenegro.

The purpose of this work is (i) to work out a test procedure for quality assurance (QA) in digital mammography with newly released test equipment, including the MagicMax mam multimeter (IBA, Germany) and the anthropomorphic tissue equivalent phantom Mammo AT (IBA, Germany), and (ii) to determine whether a first digital computer radiography (CR) system in Montenegro meets the current European standards. Tested parameters were tube output (µGy mAs(-1)) and output rate (mGy s(-1)), reproducibility and accuracy of tube voltage, half value layer, reproducibility and accuracy of the AEC system, exposure control steps, image receptor's response function, image quality and printer stability test. The evaluated dosimetric quantity is the average glandular dose (AGD) as evaluated from PMMA slabs simulating breast tissue. The main findings are that QA can be organised in Montenegro. (1) All measured parameters are within the range described in European protocols except the tube voltage which deviated more than ± 1 kV. The automatic determination of the HVL was satisfactorily. AGD ranged from 0.66 to 7.02 mGy for PMMA thicknesses from 20 to 70 mm, and is in accordance with literature data. (2) The image quality score as obtained with the anthropomorphic tissue equivalent phantom Mammo AT for the CR system was similar to findings on the authors' conventional screen-film mammography. (3) In clinical practice the mammograms are printed. The CR reader produces images with a pixel size of 43.75 µm, which is compatible with the laser printer (39 µm laser spot spacing). The image processing algorithm embedded in the reader successfully processes mammograms with desirable image brightness and contrast in the printed image. The authors conclude that this first digital mammography system seems a good candidate for breast cancer screening applications.

National DRLs for adult body CT scans based on body width

National DRLs for adult body CT scans based on body width

Effective detective quantum efficiency for two mammography systems: Measurement and comparison against established metrics

The aim of this paper was to illustrate the value of the new metric effective detective quantum efficiency (eDQE) in relation to more established measures in the optimization process of two digital mammography systems. The following metrics were included for comparison against eDQE: detective quantum efficiency (DQE) of the detector, signal difference to noise ratio (SdNR), and detectability index (d') calculated using a standard nonprewhitened observer with eye filter. The two systems investigated were the Siemens MAMMOMAT Inspiration and the Hologic Selenia Dimensions. The presampling modulation transfer function (MTF) required for the eDQE was measured using two geometries: a geometry containing scattered radiation and a low scatter geometry. The eDQE, SdNR, and d' were measured for poly(methyl methacrylate) (PMMA) thicknesses of 20, 40, 60, and 70 mm, with and without the antiscatter grid and for a selection of clinically relevant target/filter (T/F) combinations. Figures of merit (FOMs) were then formed from SdNR and d' using the mean glandular dose as the factor to express detriment. Detector DQE was measured at energies covering the range of typical clinically used spectra. The MTF measured in the presence of scattered radiation showed a large drop at low spatial frequency compared to the low scatter method and led to a corresponding reduction in eDQE. The eDQE for the Siemens system at 1 mm(-1) ranged between 0.15 and 0.27, depending on T/F and grid setting. For the Hologic system, eDQE at 1 mm(-1) varied from 0.15 to 0.32, again depending on T/F and grid setting. The eDQE results for both systems showed that the grid increased the system efficiency for PMMA thicknesses of 40 mm and above but showed only small sensitivity to T/F setting. While results of the SdNR and d' based FOMs confirmed the eDQE grid position results, they were also more specific in terms of T/F selection. For the Siemens system at 20 mm PMMA, the FOMs indicated Mo/Mo (grid out) as optimal while W/Rh (grid in) was the optimal configuration at 40, 60, and 70 mm PMMA. For the Hologic, the FOMs pointed to W/Rh (grid in) at 20 and 40 mm of PMMA while W/Ag (grid in) gave the highest FOM at 60 and 70 mm PMMA. Finally, DQE at 1 mm(-1) averaged for the four beam qualities studied was 0.44 ± 0.02 and 0.55 ± 0.03 for the Siemens and Hologic detectors, respectively, indicating only a small influence of energy on detector DQE. Both the DQE and eDQE data showed only a small sensitivity to T/F setting for these two systems. The eDQE showed clear preferences in terms of scatter reduction, being highest for the grid-in geometry for PMMA thicknesses of 40 mm and above. The SdNR and d' based figures of merit, which contain additional weighting for contrast and dose, pointed to specific T/F settings for both systems.

SU‐E‐I‐30: Simulation of the Scatter Energy Spectrum for Multiple C‐Arm/patient Thickness Configurations Using MCNPX

Purpose: Lead‐free composite aprons consist of a mixture of relatively low atomic number materials with K shell absorption edges that have been selected to provide maximum X‐ray attenuation per unit mass of the apron for common x‐ray energy spectra encountered in fluoroscopy. The purpose of this study was to simulate and then analyze several factors that may influence the energy spectrum encountered by a physician near the fluoroscopy table. Methods: Dose curves were determined on a Siemens Artis Zee C‐arm system using varying thicknesses of PMMA. A model energy spectrum was generated using SPEKTR for patients of varying size based on the filtration and kVp described by the dose curves. The energy spectrum was imported into MCNPX v2.5.0 and a Monte Carlo simulation performed. Simulated geometries included both AP and lateral, with the physician standing on both the tube and detector side of the bed. Multiple flux tallies were created to generate an energy fluence histogram as a function of physician location for each fluoroscopy geometry. Plots of the energy spectrum were generated from the resultant MCNPX tallies. Results: The average energy of the scatter spectrum varied weakly as a function of C‐arm orientation and physician location relative to C‐arm isocenter. The average energy was the highest at a location of 40 cm inferior at the detector side for a lateral exam at 43.67 keV. The average energy was the lowest at 160 cm inferior on the source side for a lateral exam at 39.82 keV. Conclusion: The influence of physician location and C‐arm geometry on the scatter spectrum was, at its largest, 3.9 keV. The difference in energy was relatively small and provides a well‐defined target region for material‐composite aprons to optimally attenuate scattered photons.