X-ray Beam Quality Research Articles

Calculation of X-ray spectra characteristics and kerma to personal dose equivalent Hp(10) conversion coefficients: Experimental approach and Monte Carlo modeling

This work aims to establish some X-ray qualities recommended by the International Standard Organization (ISO) using the half-value layer (HVL) and Hp(10) dosimetry approaches. The HVL values of the following qualities N-60, N-80, N-100, N-150 and N-250 were determined using various attenuation layers. The obtained results were compared to those of reference X-ray beam qualities and a good agreement was found (difference less than 5% for all qualities). The GAMOS (Geant4-based Architecture for Medicine-Oriented Simulations) radiation transport Monte Carlo toolkit was employed to simulate the production of X-ray spectra. The characteristics HVLs, mean energy and the spectral resolution of simulated spectra have been calculated and turned out to be conform to the ISO reference ones (difference less than the limit allowed by ISO). Furthermore, the conversion coefficients from air kerma to personal dose equivalent for simulated and measured spectra were fairly similar (the maximum difference less than 4.2%).

GAMOS/GEANT4 simulation and comparison study of X-ray narrow-spectrum series at the national Secondary Standard Dosimetry Laboratory of Morocco

This study aimed to simulate the X-ray Irradiator narrow-spectrum series and compare the results with experimental and recommended values in ISO standards. X-Ray beam qualities of N-40 to N-300 were established experimentally at the national Secondary Standard Dosimetry Laboratory (SSDL) of Morocco in purpose of calibrating radiation protection- level. The variations between the first half-value layer (1st HVL) and the second (2nd HVL) for experimental were within 5%. Also, homogeneity coefficients h were mostly between 0.75 and 1 according to ISO. GAMOS Monte Carlo code was used to simulate the radiation quality of narrow-spectrum series between N-40 to N-150. All 1st HVL, 2nd HVL, and h simulation values were compare with experimental and ISO values. In MC codes and GAMOS, there is no direct way to generate the X-ray spectrum if we do not have details of the X-ray tube geometry, dimensions and materials. Therefore, Institute of Physics and Engineering in Medicine report number 78 was used to generate the X-ray spectrums in purpose to test this method accuracy. The simulation results for the 1st HVL and 2nd HVL showed a good agreement with experimental data and with ISO 4037–1:1996 given values. Also, the comparison results showed that most of the homogeneity coefficients are within the ISO standard range.

Monte Carlo determination of a nanoDot OSLD response using quality index for diagnostic kilovoltage X-ray beams.

This study aims to investigate the energy response of an optically stimulated luminescent dosimeter known as nanoDot for diagnostic kilovoltage X-ray beams via Monte Carlo calculations. The nanoDot response is calculated as a function of X-ray beam quality in free air and on a water phantom surface using Monte Carlo simulations. The X-ray fluence spectra are classified using the quality index (QI), which is defined as the ratio of the effective energy to the maximum energy of the photons. The response is calculated for X-ray fluence spectra with QIs of 0.4, 0.5, and 0.6 with tube voltages of 50-137.6kVp and monoenergetic photon beams. The surface dose estimated using the calculated response is verified by comparing it with that measured using an ionization chamber. The nanoDot response in free air for monoenergetic photon beams (QI=1.0) varies significantly at photon energies below 100keV and reaches a factor of 3.6 at 25-30keV. The response differs by up to approximately 6% between QIs of 0.4 and 0.6 for the same half-value layer (HVL). The response at the phantom surface decreases slightly owing to the backscatter effect, and it is almost independent of the field size. The agreement between the surface dose estimated using the nanoDot and that measured using the ionization chamber for assessing X-ray beam qualities is less than 2%. The nanoDot response is indicated as a function of HVL for the specified QIs, and it enables the direct surface dose measurement.

Comparação entre métodos de medição da camada semi-redutora em radiologia

The Half Value Layer (HVL) is a parameter used in Quality Control (QC), to evaluate the X-ray beam quality. The HVL can be measured through the X-ray primary beam attenuation measurement using knew thickness slabs of 99% purity aluminum (M1) or by adjusting the best curve (M2) or by multipurpose dosimeter (solid state detector) (M3). The M1 wears out the X-ray tube more and requires a long time of data acquisition and processing, however, it is the standard recommended method for the Radiological Safety Manual. The last one method (M3) is practical, and is not influenced by the abrupt change in the X-ray transmission spectrum, as it does not require the use of aluminum plates. The equipment used to measure radiation was the NOMEX dosemeter, Cobia Smart, UNFORS XI and Radcal Ionization Chamber. The sources were mobile and fixed X-rays and mammography equipment. The results showed that the biggest difference was 15.6% between M1 and M3 for mammography equipment with a filter\target W\Rh. For conventional X-rays, that the target-filter combination is W\Al, the biggest difference was 3.3% between M1 and M3. Thus, the results show that the HVL estimate can be performed by any of the three methods or equipment, as long as the target\filter combination is W/Al. For filter\target combination other than W/Al the percentage differences increase considerably and we do not recommend the use of M1 for this type of measurement.

Prior-image-based CT reconstruction using attenuation-mismatched priors

Prior-image-based reconstruction (PIBR) methods are powerful tools for reducing radiation doses and improving the image quality of low-dose computed tomography (CT). Apart from anatomical changes, prior and current images can also have different attenuations because they originated from different scanners or from the same scanner but with different x-ray beam qualities (e.g., kVp settings, beam filters) during data acquisition. In such scenarios, with attenuation-mismatched priors, PIBR is challenging. In this work, we investigate a specific PIBR method, called statistical image reconstruction, using normal-dose image-induced nonlocal means regularization (SIR-ndiNLM), to address PIBR with such attenuation-mismatched priors and achieve quantitative low-dose CT imaging. We propose two corrective schemes for the original SIR-ndiNLM method, (1) a global histogram-matching approach and (2) a local attenuation correction approach, to account for the attenuation differences between the prior and current images in PIBR. We validate the efficacy of the proposed schemes using images acquired from dual-energy CT scanners to simulate attenuation mismatches. Meanwhile, we utilize different CT slices to simulate anatomical mismatches or changes between the prior and the current low-dose image. We observe that the original SIR-ndiNLM introduces artifacts to the reconstruction when an attenuation-mismatched prior is used. Furthermore, we find that a larger attenuation mismatch between the prior and current images results in more severe artifacts in the SIR-ndiNLM reconstruction. Our two proposed corrective schemes enable SIR-ndiNLM to effectively handle the attenuation mismatch and anatomical changes between the two images and successfully eliminate the artifacts. We demonstrate that the proposed techniques permit SIR-ndiNLM to leverage the attenuation-mismatched prior and achieve quantitative low-dose CT reconstruction from both low-flux and sparse-view data acquisitions. This work permits robust and reliable PIBR for CT data acquired using different beam settings.

A parametric study of occupational radiation dose in interventional radiology by Monte-Carlo simulations.

This paper presents the results of a parametric study on the occupational exposure in interventional radiology to explore the influence of various variables on the staff doses. These variables include the angiography beam settings: x-ray peak voltage (kVp), added copper filtration, field diameter, beam projection and source to detector distance. The study was performed using Monte-Carlo simulations with MCNPX for more than 5600 combinations of parameters that account for different clinical situations. Additionally, the analysis of the results was performed using both multiple and random forest regression to build a predictive model and to quantify the importance of each variable when the variables simultaneously change. Primary and secondary projections were found to have the most effect on the scatter fraction that reaches the operator followed by the effect of changing the x-ray beam quality. The effect of changing the source to image intensifier distance had the lowest effect.

Absorbed dose in the operator’s brain in interventional radiology practices: evaluation through KAP value conversion factors

In order to address the recent concerns over a possible increasing in brain tumour mortality among interventional radiologists and cardiologist, this work evaluated the exposure conditions of the operator’s brain during interventional procedures using Monte Carlo simulations with anthropomorphic phantoms. The absorbed doses in several predefined segments of the operator’s brain were estimated in a typical interventional radiology irradiation scenario. The doses were normalized to the KAP values simulated for ten X-ray beam qualities and four projections (PA, RAO 25°, LAO 25° and CRA 25°). For the interventional radiology scenario, because of the position of the operator, no difference was found in the exposure between the left and right regions of the brain for the first operator. However, for the second operator standing at a farer distance from the tube, the exposure of the left part of the brain is up to two times higher than that of the right part. The results are in agreement with dose measurements reported in the literature. The conversion factors, obtained as the absorbed dose per KAP, can be used to obtain a first estimate of the exposure of the brain of the operators during interventional procedures.

Absorbed dose to water determination for kilo-voltage X-rays using alanine/EPR dosimetry systems

Alanine's relative response to kilo-voltage X-rays, compared to 60Co reference quality beam, was studied in this work, in order to determine correction factors to be applied to alanine's response when irradiated with low to medium energy X-rays (up to 300 keV).The relative response to kilo-voltage X-rays of Aerial's alanine dosimeters was determined by three distinct methods: experimental measurements using alanine dosimeters and a calibrated PTW Farmer 30013 ion chamber, Monte Carlo simulations using MCNPX code and finally, analytical calculations based on weighting of X-ray spectra by NIST's published mass energy absorption coefficients. Two sets of X-ray beam qualities, covering high voltages ranging from 50 kV up to 280 kV, were used to study the energy dependence of the alanine dosimeter's response. Obtained results were consistent within 2.1% (average standard deviation at k = 1).

Image quality determination of a novel digital detector for X-ray imaging and cone-beam computed tomography applications

The demand for adequate image quality with low radiation doses for patients has greatly increased. This is especially true in the case of position verification in radiotherapy which requires a high number of images per patient. This study presents a physical characterisation of a new clinical detector named “Lassena (CsI)” based on a thick layer of structured thallium activated caesium iodide and complementary metal-oxide semiconductor technology with active pixel sensor architecture for general X-ray imaging and cone-beam computed tomography (CBCT) applications. We made a critical appraisal of its performance for the first time and determined its signal transfer property (STP) and its detective quantum efficiency (DQE) by acquiring the pre-sampling modulation transfer function (pMTF) and normalised noise power spectrum (NNPS) in addition to the dark current calculation. The investigation was conducted with the application of three X-ray beam qualities: (50 kV (RQA3), 70 kV (RQA5) and 90 kV (RQA7)) in compliance with the International Electrotechnical Commission (IEC 62220-1(2003)) standard. The STP was found to be linear with the coefficient of determination (R2) more than 0.9995 in all cases. The spatial resolution and NNPS results led to acceptable DQE values at all energies; in particular the DQE values at 0.5 line pairs per mm (DQE(0.5)) which were 0.46 for RQA3, 0.52-0.56 for RQA5 and 0.55-0.59 for RQA7. Lastly, the dark current was 2.51 pA/cm2 for a 50μm pixel pitch. For CBCT applications, Lassena (CsI) showed very promising results.

Development and Implementation of an End-To-End Test for Absolute Dose Verification of Small Animal Preclinical Irradiation Research Platforms

Lack of standardization and inaccurate dosimetry assessment in preclinical research is hampering translational opportunities for new radiation therapy interventions. The aim of this work was to develop and implement an end-to-end dosimetry test for small animal radiation research platforms to monitor and help improve accuracy of dose delivery and standardization across institutions. The test is based on a bespoke zoomorphic heterogeneous mouse and WT1 Petri dish phantoms with alanine as a reference detector. Alanine measurements within the mouse phantom were validated with Monte Carlo simulations at 0.5 mm Cu x-ray reference beam. Energy dependence of alanine in medium x-ray beam qualities was taken into consideration. For the end-to-end test, treatment plans considering tissue heterogeneities were created in Muriplan treatment planning systems (TPS) and delivered to the phantoms at 5 institutions using Xstrahl's small animal irradiation platforms. Mean calculated dose to the pellets were compared with alanine measured dose. Monte Carlo simulations and in phantom alanine measurements in NPL's reference beam were in excellent agreement, validating the experimental approach. At 1 institute, initial measurements showed a larger than 12% difference between calculated and measured dose caused by incorrect input data. The physics data used by the calculation engine were corrected, and the TPS was recommissioned. Subsequent end-to-end test measurements showed differences <5%. With an anterior field, 4 of the participating institutes delivered dose within 5% to both phantoms. An end-to-end dosimetry test was developed and implemented for dose evaluation in preclinical irradiation with small animal irradiation research platforms. The test was capable of detecting treatment planning commissioning errors and highlighted critical elements in dose calculation. Absolute dosimetry with alanine in relevant preclinical irradiation conditions showed reasonable levels of accuracy compared with TPS calculations. This work provides an independent and traceable dosimetric validation in preclinical research involving small animal irradiation.

Effect of tin filter-based spectral shaping CT on image quality and radiation dose for routine use on ultralow-dose CT protocols: A phantom study

PurposeThe purpose of this study was to assess the impact of tin filter (TF) on X-ray beam quality, image quality and radiation dose and its suitability for routine use for chest and lumbar-spine/pelvis-hip ultralow-dose (ULD) CT examination protocols. Materials and methodsThe X-ray beam quality was determined by measuring the half-value layer (HVL) and calculating the mean weighted energy for 100, 120, 150kVp (using standard filtration) and for 100 and 150kVp using TF (Sn100kVp and Sn150kVp, respectively). Acquisitions were performed on a phantom at four dose levels for each previously definedkVp. The mean attenuation (NCT), noise-power-spectrum (NPS) and task-based transfer function (TTF) were computed. The detectability index (d’) was computed to model the detection of two lesions in spine and pelvic/hip examination and two for chest exploration. Image quality and detectability using a TF were assessed for two routinely used ULD protocols. ResultsThe HVL and mean weighted energy increased using a TF for the same tube voltage. Using a TF for the same tube voltage changed NCT for bone and acrylic inserts, decreased the NPS peak without changing the NPS spatial frequency and increased the TTF values. The d’ values were improved using a TF and with the dose increase. d’ values of all modeled lesions were improved using Sn100kVp and Sn150kVp for the lumbar-spine/pelvis-hip and chest ULD protocols except for sclerotic bone lesion using Sn150kVp. ConclusionThe use of TF increases the X-ray beam quality and improves the image quality characteristics in phantom images, thus appearing as a promising tool for reducing dose and/or improving the image quality of ULD protocols.

Investigation of a synthetic diamond detector response in kilovoltage photon beams.

An important characteristic of radiation dosimetry detectors is their energy response which consists of absorbed-dose and intrinsic energy responses. The former can be characterized using Monte Carlo (MC) simulations, whereas the latter (i.e., detector signal per absorbed dose to detector) is extracted from experimental data. Such a characterization is especially relevant when detectors are used in nonrelative measurements at a beam quality that differs from the calibration beam quality. Having in mind the possible application of synthetic diamond detectors (microDiamond PTW 60019, Freiburg, Germany) for nonrelative dosimetry of low-energy brachytherapy (BT) beams, we determined their intrinsic and absorbed-dose energy responses in 25-250kV beams relative to a 60 Co beam, which is usually the reference beam quality for detector calibration in radiotherapy. Three microDiamond detectors and, for comparison, two silicon diodes (PTW 60017) were calibrated in terms of air-kerma free in air in six x-ray beam qualities (from 25 to 250kV) and in terms of absorbed dose to water in a 60 Co beam at the national metrology laboratory in Sweden. The PENELOPE/penEasy MC radiation transport code was used to calculate the absorbed-dose energy response of the detectors (modeled based on blueprints) relative to air and water depending on calibration conditions. The MC results were used to extract the relative intrinsic energy response of the detectors from the overall energy response. Measurements using an independent setup with a single ophthalmic BEBIG I25.S16 125 I BT seed (effective photon energy of 28keV) were used as a qualitative check of the extracted intrinsic energy response correction factors. Additionally, the impact of the thickness of the active volume as well as the presence of extra-cameral components on the absorbed-dose energy response of a microDiamond detector was studied using MC simulations. The relative intrinsic energy response of the microDiamond detectors was higher by a factor of 2 in 25 and 50kV beams compared to the 60 Co beam. The variation in the relative intrinsic energy response of silicon diodes was within 10% over the investigated photon energy range. The use of relative intrinsic energy response correction factors improved the agreement among the absorbed dose to water values determined using microDiamond detectors and silicon diodes, as well as with the TG-43 formalism-based calculations for the 125 I seed. MC study of microDiamond detector design features provided a possible explanation for inter-detector response variation at low-energy photon beams by differences in the effective thickness of the active volume. MicroDiamond detectors had a non-negligible variation in the relative intrinsic energy response (factor of 2) which was comparable to that in the absorbed-dose energy response relative to water at low-energy photon beams. Silicon diodes, in contrast, had an absorbed-dose energy dependence on photon energy that varied by a factor of 6, whereas the intrinsic energy dependence on beam quality was within 10%. It is important to decouple these two responses for a full characterization of detector energy response especially when the user and reference beam qualities differ significantly, and MC alone is not enough.

Evaluation of X-ray beam quality in different bowtie filters on ultra-high resolution CT

Evaluation of X-ray beam quality in different bowtie filters on ultra-high resolution CT

Organ-specific dose coefficients derived from Monte Carlo simulations for historical (1930s to 1960s) fluoroscopic and radiographic examinations of tuberculosis patients

This work provides dose coefficients necessary to reconstruct doses used in epidemiological studies of tuberculosis patients treated from the 1930s through the 1960s, who were exposed to diagnostic imaging while undergoing treatment. We made use of averaged imaging parameters from measurement data, physician interviews, and available literature of the Canadian Fluoroscopy Cohort Study and, on occasion, from a similar study of tuberculosis patients from Massachusetts, United States, treated between 1925 and 1954. We used computational phantoms of the human anatomy and Monte Carlo radiation transport methods to compute dose coefficients that relate dose in air, at a point 20 cm away from the source, to absorbed dose in 58 organs. We selected five male and five female phantoms, based on the mean height and weight of Canadian tuberculosis patients in that era, for the 1-, 5-, 10-, 15-year old and adult ages. Using high-performance computers at the National Institutes of Health, we simulated 2,400 unique fluoroscopic and radiographic exposures by varying x-ray beam quality, field size, field shuttering, imaged anatomy, phantom orientation, and computational phantom. Compared with previous dose coefficients reported for this population, our dosimetry system uses improved anatomical phantoms constructed from computed tomography imaging datasets. The new set of dose coefficients includes tissues that were not previously assessed, in particular, for tissues outside the x-ray field or for pediatric patients. In addition, we provide dose coefficients for radiography and for fluoroscopic procedures not previously assessed in the dosimetry of this cohort (i.e. pneumoperitoneum and chest aspirations). These new dose coefficients would allow a comprehensive assessment of exposures in the cohort. In addition to providing newly derived dose coefficients, we believe the automation and methods developed to complete these dosimetry calculations are generalizable and can be applied to other epidemiological studies interested in an exposure assessment from medical x-ray imaging. These epidemiological studies provide important data for assessing health risks of radiation exposure to help inform the current system of radiological protection and efforts to optimize the use of radiation in medical studies.

Measurement of X-ray Beam Quality and Patient Dose Information from Analog Mammography

Measurement of X-ray beam quality and patient dose information from analog mammography have been studied by using an X-ray multimeter from 2016-2018. Parameters in the study are voltage accuracy, reproducibility test, radiation output linearity, radiation beam quality test, and patient dose information. The patient dose information using PMMA phantom with a thickness 4 cm in the Mean Glandular Dose (MGD) obtained dose values in 2016, 2017, 2018 are 0.982 mGy, 0.982 mGy, 0.953mGy, respectively. This study aims to determine the feasibility of mammography, while patient doses are compared with the standars set by the IAEA. The results showed that the suitability test of X-ray beam quality and patient dose information still comply the requirements recommended by the IAEA.

Methodology adopted to establish diagnostic X-ray beam qualities

Methodology adopted to establish diagnostic X-ray beam qualities

Commissioning and performance characteristics of a pre-clinical image-guided radiotherapy system

Characteristics of a small-animal radiotherapy device, the X-RAD SmART, are described following commissioning of the device for pre-clinical radiotherapy research. Performance characteristics were assessed using published standards and compared with previous results published for similar systems. Operational radiation safety was established. Device X-ray beam quality and output dose-rate were found to be consistent with those reported for similar devices. Output steadily declined over 18 months though remained within tolerance levels. There is considerable variation in output factor across the international installations for the smallest field size (varying by more than 30% for 2.5 mm diameter fields). Measured depth dose and profile data was mostly consistent with that published, with some differences in penumbrae and generally reduced flatness. Target localisation is achieved with an imaging panel and with automatic corrections for panel flex and device mechanical instability, targeting within 0.2 mm is achievable. The small-animal image-guided radiotherapy platform has been implemented and assessed and found to perform as specified. The combination of kV energy and high spatial precision make it suitable for replicating clinical dose distributions at the small-animal scale, though dosimetric uncertainties for the narrowest fields need to be acknowledged.

Ion chamber response to kilovoltage x-rays in the presence of a contrast agent

Contrast enhanced radiotherapy is a relatively new treatment modality in which a radiological contrast agent is uploaded into a tumor that is subsequently irradiated with kilovoltage x-ray beams thus maximizing absorption of radiation through the photoelectric effect. As with other treatment modalities, experimental verification of absorbed dose distributions is a necessary step as part of the quality assurance process. In this paper, we address the question of how the response to kilovoltage x-rays exhibited by an ion chamber is modified when a radiological contrast agent is incorporated into the irradiated medium. Using a combination of Monte Carlo simulation and experimental validation of the different models used in such simulations, we determined the correction factors that allow for the use of an ion chamber with a ND,W calibration factor at a given kilovoltage x-ray beam quality Q to be used when said beam irradiates a medium into which a radiological contrast agent is incorporated. The correction factors were derived as a function of the contrast agent concentration and for five different beam qualities. For a given concentration, the correction factor varies linearly with the beam quality as defined by the half-value layer, and for a given beam quality it varies linearly with the contrast agent concentration.

WALL THICKNESS OPTIMISATION OF AN IONISATION CHAMBER FOR DIRECTIONAL DOSE EQUIVALENT RATE MEASUREMENT AT LOW AND MEDIUM PHOTON ENERGIES.

A thin and plane wall ionisation chamber having 900 cc volume was designed and fabricated to study the calibration coefficient dependency on ionisation chamber wall thickness for directional dose equivalent rate (Ḣ'(d)) at various low and medium energy X-ray beam qualities. Optimised wall thickness was established through measurements to achieve a near flat energy response using the developed ionisation chamber. The measurement shows that in the energy range 12-213 keV, the average calibration coefficient for directional dose equivalent rate lies within ±10% for wall thickness 1.2 mg/cm2 and 480 mg/cm2 (4 mm poly methyl methacrylate) for skin and eye lens dose monitoring, respectively. The study could be useful for the estimation of skin and eye lens doses for the paramedical staff and patient during the interventional radiology and interventional cardiology procedures by monitoring the directional dose equivalent rate.

P061] Calculation of beam quality parameters for X-ray mammography spectra: A monte carlo simulation study

Purpose Breast cancer is known to be the most malignant type of cancer among women in the world. By X-ray mammographic imaging, the disease can be detected and then an early stage treatment can be started following this. For a reliable imaging, beam quality parameters should be precisely determined. However, measurement of X-ray beam quality parameters necessitates using specific equipment. An efficient way for determining these parameters is to utilize scientifically proven and verified Monte Carlo simulation codes. Methods Monte Carlo simulations are widely used in digital mammography imaging research. In this work, MCNP5 was used for simulating generation of X-ray spectrum including both bremsstrahlung and characteristic X-rays. Electron beam and target (anode) were modelled as specified in the Report of AAPM Task Group 195: Monte Carlo Reference Data Sets for Imaging Research. Results X-ray quality parameters such as Aluminum (Al) equivalent half-value layer (HVL), Al equivalent effective energy, average energy, and air kerma of the simulated polyenergetic X-ray beams were calculated and tabulated for a wide range of commercially available mammographic X-ray tube voltage (kVp) and target/filter material and thickness combinations (molybdenum/molybdenum, molybdenum/rhodium, rhodium/rhodium, tungsten/rhodium, tungsten/silver, and tungsten/aluminum). All calculated parameters were then fitted to second-degree polynomial surface equations as a function of kVp and filter thickness for each target/filter combination. Conclusions This work is essential and flexible in the sense that it provides a reliable and quick look-up database for those performing mammographic patient dose and image quality calculations. In addition, it could be taken as a starting point for generation of quality data for entire diagnostic X-ray energy range, e.g. 20–140 kVp, for any combination of target/filter. On the other hand, with this study, it can be deduced that important mammographic parameters can be precisely calculated with Monte Carlo methods, which would otherwise need for expensive and complicated experimental equipment and much more time.