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Mammography is one of the most effective diagnostic methods for the early detection of breast cancer; however, it poses the risk of radiation exposure. To date, mammography dosimetry has been performed according to the mean glandular dose; however, the actual exposure in the breast has not been assessed. Here, we have measured dose distributions and depth doses using both radiochromic films and mammographic phantoms, and a three-dimensional intra-mammary dose assessment was conducted. The absorbed dose distribution at the surface was markedly higher on the chest wall side but lower on the nipple side. The absorbed doses in the depth direction exponentially decreased. The glandular tissue near the surface may be irradiated with an absorbed dose of 7.0 mGy or higher. Since LD-V1 could be placed inside the phantom, the absorbed dose inside the breast could also be evaluated in three dimensions.

This study developed a phantom with a shape similar to that of the breast and use GAFCHROMIC films that can be placed inside the phantom to measure the detailed breast dose distribution in mammography. GAFCHROMIC EBT3 was placed on the block cube breast phantom and irradiated with a mammography device to measure the absorbed dose distribution inside the phantom in the horizontal and depth directions. The dose distribution in the horizontal plane was the highest in the centre on the chest wall side, and it decreased in a fan shape. Along the depth of the phantom, the doses absorbed across the entire cross-section were 16.15 mGy at the surface and 7.51, 3.25 and 1.68 mGy at depths of 10, 20 and 30 mm, respectively. Compared with the mean glandular dose, the proposed method can measure breast dose distributions in greater detail and is applicable to various breast shapes.

In this paper, we propose a novel radiochromic film (RCF)-based computed tomography (CT) dosimetry method, which is different from the method based on CT dose index. RCF dosimetry using Gafchromic QA2 films was performed using two lengths of film-folding phantoms. The phantom was exposed to X-ray CT through a single scan, while the RCF was sandwiched between the phantoms. We analysed the dose profile curve in two directions to investigate the dose distribution. We observed a difference in the dose distribution as the phantom size changed. Our results contradict with the results of previous studies such as Monte Carlo simulation or direct measurement. The ability to visually evaluate 2D dose distributions is an advantage of RCF dosimetry over other methods. This research investigated the ability of 2D X-ray CT dose evaluation using RCF and film-folding phantom.

The effective energy calculated using the half-value layer (HVL) is an important parameter for quality assurance (QA) and quality control (QC). However constant monitoring has not been performed because measurements using an ionization chamber (IC) are time-consuming and complicated. To solve these problems, a method using radiochromic film (GAFCHROMIC EBT2 dosimetry film (GAF-EBT2) with slight energy dependency errors), a mobile scanner and step-shaped aluminum (SSAl) filter is developed. The results of the method using a mobile scanner were compared with those of the recommended method using an IC in order to evaluate its applicability. The difference ratios of the effective energies by each method using a mobile scanner with GAF-EBT2 were less than 5% compared with results of an IC. It is considered that this method offers a simple means of determining HVL for QA and QC consistently and quickly without the need for an IC dosimeter.

This research demonstrated that commercially available alumina is well-suited for use in large area X-ray detectors. We discovered a new radiation imaging device that has a high spatial resolution, high sensitivity, wide dynamic range, large imaging area, repeatable results, and low operating costs. The high thermoluminescent (TL) properties of Al2O3 ceramic plates make them useful for X-ray imaging devices.

Radiochromic film dosimeters have a disadvantage in comparison with an ionization chamber in that the dosimetry process is time-consuming for creating a density-absorbed dose calibration curve. The purpose of this study was the development of a simplified method of creating a density-absorbed dose calibration curve from radiochromic film within a short time. This simplified method was performed using Gafchromic EBT3 film with a low energy dependence and step-shaped Al filter. The simplified method was compared with the standard method. The density-absorbed dose calibration curves created using the simplified and standard methods exhibited approximately similar straight lines, and the gradients of the density-absorbed dose calibration curves were -32.336 and -33.746, respectively. The simplified method can obtain calibration curves within a much shorter time compared to the standard method. It is considered that the simplified method for EBT3 film offers a more time-efficient means of determining the density-absorbed dose calibration curve within a low absorbed dose range such as the diagnostic range.

The noise properties of a radiography system are commonly described by its wiener spectrum (WS). The two-dimensional discrete Fourier transform (2D-DFT) methods is the most commonly used and accepted techniques for measuring the digital WS. The 2D-DFT method has been adopted by the International Electrotechnical Commission (IEC) as a noise-power spectrum. However, the digital WS contains the effects of aliasing error, and this error depends on the presampled modulation transfer function (MTF) of the digital radiography (DR) system. The aim of this work was to show the influence of the aliasing error of the digital WS when the image resolution property was changed. We examined the influence of the aliasing error using simulated noise images. Two types of noise images with same pixel size and different presampled MTFs were generated by using ImageJ (National Institutes of Health: NIH). These images were used to simulate the image resolutions of an indirect/direct flat panel detector (FPD). The theoretical WS of the simulation noise image can be derived from a standard deviation σ of the Gaussian filter and added noise. Simulated noise images were analysed using the 2D-DFT method. The WS values calculated from those simulation images were compared with the theoretical WS values. The WS values in the indirect and direct FPD increased, compared to the theoretical WS values. The average relative differences for frequencies up to the Nyquist frequency were 27.9% and 85.2%, respectively. The results showed that the degree of the influence of the aliasing error of the digital WS depends largely on the presampled MTF of the DR system. Therefore, we should take into account the impact of the aliasing error of the digital WS, in the comparison between DR systems with different presampled MTFs.

Radiochromic films (RFs) have been developed for the measurement of the absorbed dose of low-energy photons. RFs are self-developing and radiation sensitive, and the amount of darkening is proportional to the absorbed dose. RFs are easy to handle due to their insensitivity to interior room light. However, the precision of the measurement has been questioned because of the change in density caused by the scan timing of the image acquisition using a flat-bed scanner. In this study, the density change of a flat-bed scanner was investigated using the temporal and the repetition scans. To obtain the image density, Gafchromic XR-QA2 films (XR-QA2s) were irradiated at 0 and 20 mGy (air-kerma) using 75 kVp (30 keV). The XR-QA2s were scanned every hour (0–6 h) from power activation to investigate the temporal light source change of a flat-bed scanner (EPSON ES-10000G). In addition, ten consecutive scans were performed every hour. The scan parameters were RGB (48-bit) mode, 100 dpi, and reflection mode. Image data of the XR-QA2s were divided into R, G, and B modes, and the R (16-bit) mode was used. The temporal light source change after power activation was small. However, in ten consecutive scans, the density of the first scan was the highest. The densities decreased with more scans. This result indicated that the precision of the dose measurement has about a 3% error due to the repeated scans. To obtain an accurate dose measurement, the image data obtained under the same conditions, such as the same time from power activation or same number of consecutive scans, must be used.

The growing use of multiple small fields in radiotherapy treatments such as intensity-modulated radiation therapy has increased the importance of small-field dosimetry. In this study, we investigate the settling response of a set of ionization chambers exposed to 4, 6, and 10 MV stereotactic radiotherapy X-ray fields. Previous studies had reported that lack of pre-irradiation could result in settling response errors of up to several percentage points. While the use of ionization chambers does contribute to this behaviour, the most obvious factors affecting the settling response appear to be the area of the insulator, the material used for the central collector electrode, and the accelerating tube. The results of this study show that Farmer-style ionization chambers with electrode connections that are guarded up to an active air volume settle quickly (within five minutes); moreover, the changes in their responses are small. On the other hand, small ionization chambers exhibit settling times of 11–24 min. In this study, the settling times of small ionization chambers were found to be dependent on the accelerating tube.

Knowledge of the effective energy of 320-multidetector computed tomography (CT) is important for quality assurance and quality control. Evaluation in two dimensions is necessary because the effective energy varies depending on the shape of the wedge filter located in the CT device. The purpose of this study was to measure the two-dimensional effective energy distribution of the CT using GAFCHROMIC EBT3 (EBT3), which has a weak energy dependence. The exposure parameters of the 320-multidetector CT were 120 kV, 500 mA, and 5.0 s, and the X-ray tube was stopped at the 0 o’clock position. To avoid scattered radiation, the distance between the EBT3 and other scatterers was set to 200 mm or more. The Al filter thickness was increased from 2 to 20 mm. The irradiated area was divided into 54 compartments, and the density attenuation ratio was measured. The half-value layers (HVLs) were determined using the density attenuation ratios. The effective energies were obtained from the HVLs, and the two-dimensional effective energy distribution was evaluated. Because the thickness of the wedge filter in the longitudinal direction (parallel to the bed) remained unchanged, the variation in the effective energy was negligible in this direction. On the other hand, in the lateral direction (perpendicular to the bed), because the wedge filter gradually thickened from the center to the side, the effective energy from the center to the side increased. The two-dimensional effective energy distribution of the CT could thus be measured using EBT3.

UV-A irradiation of Gafchromic XR-RV3 and XR-SP2 are considered to be a substitute for X-ray irradiation in the double irradiation of Gafchromic XR-RV3 and XR-SP2. It makes it possible to compensate for heterogeneity errors in the active layers of Gafchromic XR-RV3 and XR-SP2. UV-A with a wavelength of 395-nm was irradiated to Gafchromic XR-RV3 and XR-SP2, and irradiation time and color density change were investigated. At first, Gafchromic XR-RV3 and XR-SP2 were pre-irradiated for 2 and 4 hours, respectively, by UV-A with a wavelength of 365-nm, with UV-A fluorescent lamp as the radiation source, located at a distance of 72 cm. Secondly, a UV-A light emitting diode (LED) capable of generating 395-nm UV-A was used. The irradiation times of UV-A for Gafchromic XR-RV3 and XR-SP2 were from 5 to 120 minutes and from 30 to 300 minutes at a distance of 5.0 cm, respectively. From these results, appropriate irradiation time was considered. A 0.5 inchs diameter region of interest was set for each irradiation area, and a histogram of pixel values was obtained. The selected condition was two items “There is not 0 in a mode”, “A 1/10 level intersects both sleeves of graph”.

Gafchromic EBT3 (EBT3) is used as a radiochromic film in half-value layer (HVL) measurement methods, which are used to calculate the effective energy for QA and QC. HVL measurements using EBT3 display a precision of less than 5 % compared with the results of standard method with an ionization chamber (IC) dosimeter, and offer a simple procedure for determining the HVL consistently and quickly without the need for an IC. However, it is difficult to apply this technique because of the scattered radiation caused by the geometric layout of the X-ray computed tomography (CT) apparatus. In this study, the effect of scattered radiation on EBT3 is investigated. It was found that the EBT3 is not affected by scattered radiation at positions beyond 50 mm from the scattering substance. Therefore, the results suggest that EBT3 is suitable for use in X-ray CT HVL measurements. On the other hand, when the distance from the scattering substance was 10 mm or less, EBT3 showed very high absorption compared to a semiconductor detector. Therefore, EBT3 is more sensitive than the semiconductor detector at a close range and can be used to measure scattered radiation when the distance from the scattering substance is 10 mm or less.

Purpose In recent years, one of most important topic for X-ray CT examination is reducing radiation exposure. We have tried to establish the simple and accurate CT dosimetry method using radiochromic (RC) film. In this study, we investigated how the phantom diameter affects the pixel value distribution of RC film. This research is one step of quantifying dose distribution of X-ray CT using RC film. Methods The radiochromic film was exposed by a clinical CT scanner (Aquilion Lightning, Toshiba Medical Systems). Gafchromic XR-QA2 film was irradiated. The film-folding phantom consists of two acrylic semicylinder. In this study, the large phantom (cylinder cross-section diameter is 16 cm) and the small phantom (cylinder cross-section diameter is 10 cm) were used in this research. The scan parameters were as follows: non-helical scan, tube voltage = 120 kV, tube current = 300 mA, slice thickness = 2 cm, scan speed = 1 s per rotation. Image processing and analysis were performed by MATLAB (The Mathworks, Inc.) and Image J (National Institute of Health). The irradiated films were scanned by a commercial scanner (EPSON ES-10000G, Seiko Epson Co.). Results To compare the pixel value distribution using two differently sized phantom, we used the contour line analysis. The differences of distribution were observed between the large phantom and the small phantom. It was found that the distribution using the large phantom changes clearly. Conclusions In conclusion, our method may be useful for analyzing the distribution of pixel value on various conditions.

We are proposing a new simplified practical method for measuring the presampled MTF of digital radiographic systems using a “virtual slit” image from an edge image. The basic concept of our approach is the combination of the edge and slit methods. This method differs from previous methods in that it derives the Line Spread Function (LSF) without numeric differentiation of the Edge Spread Function (ESF). The accuracy and uncertainty of the new method was investigated using simulated images (whose true MTFs are known) and a clinical indirect flat panel detector (FPD). In the simulations, the new method had a higher accuracy than the IEC method. In the clinical system, both the MTFs of the new and the IEC methods are in good agreement for frequencies up to the Nyquist frequency limit (within 0.0028). The standard deviation (SD) of the MTF using the new method was comparable with that of the IEC method. The results showed that our method has a small influence on the phase error according to the edge angle and the noise reduction effect. In our method, we can calculate the LSF from a “virtual slit” image and obtain a precise presampled MTF much more easily than in previous methods.

Although GAFCHROMIC EBT3 (EBT3) as a radiochromic film shows only slight energy dependency errors in comparison with other radiochromic films, the influence of energy dependence in the diagnosis energy range (less than 100 keV) is larger in the high energy range (over 100 keV). Based on this characteristic, adaptation of the EBT3 dosimetry in the diagnosis range was investigated. The energy response of the EBT3 in the diagnosis range at 30, 40, 50, 60 keV was measured using the density-absorbed dose calibration curve of the absorbed dose versus film density for the EBT3. Various data (degree of leaning, coefficient of determination) of each effective energy were compared. The density - absorbed dose calibration curves were linearly correlated in each of the effective energies. There was an energy dependent error of approximately 0.2 % from 30 to 60 keV. As a result, it can be seen that the EBT3 is available in the diagnosis energy range. However, the influence of the non-uniformity error caused by the repeatability of the scan method must be considered because EBT3 distortion has a serious influence on measurement precision.

The resolution properties of an imaging system are commonly described by its modulation transfer function. The slit and edge methods are the two most commonly used and accepted techniques for measuring the MTF. The use of a slit requires very precise fabrication and alignment of the device in the radiation beam, a high radiation exposure to allow sufficient transmission through the narrow slit (aperture 10 μm). We took notice of the slit aperture and a new slit device with slightly wider aperture (40 μm) was made for the im-provement of the conventional slit device.The aim of this work was to show the properties such as the X-ray tube loading, the alignment and the MTF using the new slit device with slightly wider aperture. Imaging plates in the CR system were employed in this measurement.

According to the 2011 ICRP statement, the threshold in absorbed dose for the lens of the eye is now considered to be 0.5 Gy. Therefore, it is important to keep the eye lens doses during head computed tomography examination as low as reasonably achievable. In this study, the two lenses and the occiput doses associated with patient setup errors and head size were evaluated using phantoms developed for pediatric patients. The phantoms were made using flexible acrylic sheets in a cylindrical shape [diameters of 6 (premature baby), 8 (neonate), 10 (infant), and 12 cm (child)] and placed on the end of the CT bed. The bed position was raised from the center for each phantom size. The two lenses and the occiput doses at each setup were measured using radiochromic film. By raising the bed position, the two lenses doses decreased at all phantom sizes. However, the occiput doses changed in a complex manner according to the phantom size. In this study, decreasing the distance from the lens to the X-ray tube (i.e. raising the bed position) is an effective way to reduce the absorbed dose of the lens. However, when the occiput was positioned at the center of the gantry aperture, the occiput dose peaked in all phantom sizes. In addition, the results indicated a complex dose distribution in pediatric head CT when taking into account the bed position (patient setup errors) and phantom sizes. Furthermore, beam slice width and pitch are important factor in determining the maximum absorbed dose. To keep radiation doses during CT examination as low as reasonably achievable, it is important to clarify the influence of CT scanning settings on CT dose.

The effective energy calculated using the half-value layer (HVL) is an important parameter for quality assurance (QA) and quality control (QC). However constant monitoring has not been performed because measurements using an ionization chamber (IC) are time-consuming and complicated. To solve these problems, a method using radiochromic film (GAFCHROMIC EBT2 dosimetry film (GAF-EBT2) with slight energy dependency errors), a flatbed scanner and step-shaped aluminum filters has been developed. In this study, a mobile scanner was used for digital image acquisition of GAF-EBT2, because the mobile scanner has characteristics of low cost and increased portability compared with a flatbed scanner. GAF-EBT2 was scanned using the flatbed scanner in transmission mode and reflection mode, and the mobile scanner in reflection mode. The HVL (X-ray tube voltages of 120 kVp) was evaluated using the density attenuation ratio. The effective energies obtained using HVL of GAF-EBT2 (flatbed scanner, mobile scanner) and an IC dosimeter were compared. In reflection mode, both the flatbed scanner and the mobile scanner provided a flat density profile curve without the error of the light source. The difference ratios of the effective energies by each method using a flatbed scanner (reflection mode) and a mobile scanner (reflection mode) with GAF-EBT2 were less than 5 % compared with results of an IC dosimeter. It is considered that this method offers a simple means of determining HVL for QA and QC consistently and quickly without the need for an IC dosimeter.

Introduction Recently developed radiochromic films can easily measure the absorbed doses by using a flat-bed scanner. However, in a GAFCHROMIC EBT3 (EBT3) radiochromic film, the precision of the measurement was compromised because of the change in density caused by the scan timing of image acquisition using a flat-bed scanner. Purpose The purpose of this study was to investigate the temporal light source change of a flat-bed scanner affecting the density of EBT3. Materials and methods EBT3 without irradiation was used to remove non-uniformity error caused by irradiation. EBT3 was scanned every hour (0–6 h) from power activation to investigate the temporal light source change of a flat-bed scanner (EPSON ES-10000G). In addition, five consecutive scans were performed every hour. Scan parameters were RGB (48 bit) mode, 100 dpi, the reflection mode. Image data of EBT3 was divided into R, G, and B modes, and the R (16 bit) mode was used. The region of interest has a diameter of 75 pixels in the center of the EBT3 sheet. Results The density gradually decreases after power activation and became the plateau 5 h later. After the first scan, a low density is observed: the density was stable after the third scan. Conclusion To improve repeatability of EBT3, the scan must be performed only after 5 h power activation. In addition, the image data obtained after the third consecutive scan must be used. Disclosure We have no disclosure and financial support.

Purpose: The modulation transfer function (MTF) in Computed Radiography (CR) for the laser scan direction is generally lower than that for the plate scan direction. In a CR system, there are a number of different mechanisms that cause blurring. We analyzed intrinsic system factors of CR that could affect the MTF, such as afterglow, during readout and the anti-alias filter of analog to digital converter (ADC) in different scan directions. Methods and Materials: Mathematical slit and edge images were generated from analytical functions. These images were arranged perpendicularly to the laser scan and the plate scan directions, respectively. We simulated the influence of afterglow and the anti-alias filter by using Microsoft Excel. The MTFs calculated from those simulation images were compared with the theoretical MTFs obtained analytically. Results: MTFs in the laser scan direction measured with the slit and edge method were significantly lower than MTFs in the plate scan direction because of afterglow and the anti-alias filters. The degree of the influence on MTF with respect to afterglow and the anti-alias filters was different depending on the measurement method and the scan directions of CR.

The physical characteristics of a direct amorphous Selenium (a-Se) digital fluoroscopy and radiography system were investigated. Pre-sampled modulation transfer functions (MTF) were measured using a slit method. Noise power spectra were determined for different input exposures by fast Fourier transform of uniformly exposed samples. The MTFs of direct digital radiography systems showed significantly higher values than those of indirect digital radiography and screen-film systems. The direct digital radiography systems showed higher noise levels compared with those of indirect systems under roughly the same exposure conditions. Contrast-detail analysis was performed to compare detection by direct digital radiography systems with that of the screen-film (FUJI HG-M2/UR2) systems. The average contrast-detail curves of digital and film images were obtained from the results of observation. Image quality figures (IQF) were also calculated from the individual observer performance tests. The results indicated that digital contrast-detail curves and IQF are, on average, are equal those of the screen-film system.

In mammography units, the X-ray tube focal spot is located directly above the chest wall edge of the detector. Therefore, the X-ray beam is incident at a different angle along the cathode-anode axis. When the X-ray beam is incident on the imaging plate (IP) at a relatively large angle, the resolution property of a new imaging plate with dual-sided reading system would be degraded compared with the conventional imaging plate because of the parallax effect, which produces a shift in the image on two sides of the imaging plate. To evaluate the oblique incidence effect of the X-ray beam on the degradation of resolution properties and detection of simulated microcalcifications of a new CR system with a pixel size of 50 microm, its basic imaging properties and observer performance tests were compared with those of a conventional CR system. The resolution properties were evaluated by measuring modulation transfer functions (MTFs). Observer performance tests were conducted to compare the detectability of simulated microcalcifications of CR systems. Degradation of presampling MTFs for the new system is greater than that of the conventional CR system when the X-ray beam was incident at the same angle on the imaging plate. We found that the degradation of the area under the ROC curve (Az) for the new CR system was greater than that of the conventional CR system when the X-ray beam was incident at the same angle on the imaging plate.

To investigate the physical imaging properties and detection of simulated microcalcifications of a new computed radiography (CR) system with a pixel size of 50 microm for digital mammography.New and conventional CR were employed in this study. The new CR system included a high-resolution imaging plate coupled with the FCR5000MA (50 microm pixel pitch) including transparent support and a dual-sided reader. The conventional CR system was coupled with the FCR9000 (100 microm pixel pitch). Modulation transfer functions (MTFs) and Wiener spectra (WS) of the new and conventional CR systems were measured. Observer performance tests were conducted to compare the effects of pixel size (50 microm vs. 100 microm) on the diagnostic accuracy of CR systems in the detection of simulated microcalcifications.The presampling MTF of the new CR system was higher at high frequencies than the conventional CR system. The WS of the new CR system was comparable to that of the conventional CR system at all frequencies. The area under the receiver operating characteristic (ROC) curve (Az) obtained with the new CR and the conventional CR systems were 0.84 and 0.79, respectively. Results showed that the detection of simulated clustered microcalcifications was significantly improved by use of the new CR system compared with the conventional CR system (p0.05).The new CR mammography system improved physical imaging properties and detection of simulated microcalcifications over conventional CR mammography.

We measured and evaluated digital, pre-sampling and overall imaging properties (characteristic curve, modulation transfer function (MTF), Wiener spectrum (WS), noise equivalent quanta (NEQ) ) for Cannon's flat-panel detector (FPD), Fuji computed radiography (FCR) and screen-film (S/F) systems, respectively. First, the digital and overall characteristic curves of FPD and FCR systems were more wide dynamic range than that of the S/F system. Second, the pre-sampling and overall MTF of FPD system were better than those of FCR system a little at lower spatial frequencies than 0.8 mm(-1), but the overall MTF of FPD and FCR systems were worse than that of S/F system a little at all spatial frequencies. Third, the digital and overall WS of FPD system were similar or better than those of FCR system, but the overall WS of FPD and FCR systems were worse than that of S/F system. Fourth, the pre-sampling and overall NEQ of FPD system were better than those of FCR system a little at lower spatial frequencies than 1.6 mm(-1), but the overall NEQ of FPD and FCR systems were worse than that of S/F system at all spatial frequencies. Comparison of chest phantom images showed that the FPD produced images with quality comparable to or higher than those of the FCR system. From these results, we can expect that the FPD is useful machine by using digital image processing and so on in the radiology department.

In a computed radiography (CR) system, there are a number of different mechanisms that cause blurring. The aim of this study was to analyze intrinsic system factors of CR systems that could affect the modulation transfer function (MTF), such as afterglow during readout and the anti-alias filter before analog to digital converter. Methods and Materials: Mathematical slit and edge images were generated from analytical functions. These images were arranged perpendicularly to the laser scan and the plate scan directions, respectively. The influence of afterglow and the anti-alias filter was simulated by using Microsoft Excel. The MTF values calculated from those simulation images were compared with the theoretical MTF values obtained analytically. Results: MTF values in the laser scan direction measured with the slit and edge methods were significantly lower than MTF values in the plate scan direction. The degree of influence on MTF with respect to afterglow and the anti-alias filters was different depending on the measurement method and the scan directions of CR systems. The influence of the anti-alias filters mainly contributed to the differences between MTF values with the slit and edge methods in the laser scan direction.