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Objective. To introduce the optimization of a customized GPU-based simultaneous algebraic reconstruction technique (cSART) in the field of phase-contrast breast computed tomography (bCT). The presented algorithm features a 3D bilateral regularization filter that can be tuned to yield optimal performance for clinical image visualization and tissues segmentation. Approach. Acquisitions of a dedicated test object and a breast specimen were performed at Elettra, the Italian synchrotron radiation (SR) facility (Trieste, Italy) using a large area CdTe single-photon counting detector. Tomographic images were obtained at 5 mGy of mean glandular dose, with a 32 keV monochromatic x-ray beam in the free-space propagation mode. Three independent algorithms parameters were optimized by using contrast-to-noise ratio (CNR), spatial resolution, and noise texture metrics. The results obtained with the cSART algorithm were compared with conventional SART and filtered back projection (FBP) reconstructions. Image segmentation was performed both with gray scale-based and supervised machine-learning approaches. Main results. Compared to conventional FBP reconstructions, results indicate that the proposed algorithm can yield images with a higher CNR (by 35% or more), retaining a high spatial resolution while preserving their textural properties. Alternatively, at the cost of an increased image ‘patchiness’, the cSART can be tuned to achieve a high-quality tissue segmentation, suggesting the possibility of performing an accurate glandularity estimation potentially of use in the realization of realistic 3D breast models starting from low radiation dose images. Significance. The study indicates that dedicated iterative reconstruction techniques could provide significant advantages in phase-contrast bCT imaging. The proposed algorithm offers great flexibility in terms of image reconstruction optimization, either toward diagnostic evaluation or image segmentation.

Purpose: To compare, via Monte Carlo simulations, homogeneous and non-homogenous breast models adopted for mean glandular dose (MGD) estimates in mammography vs. patient specific digital breast phantoms. Methods: We developed a GEANT4 Monte Carlo code simulating four homogenous cylindrical breast models featured as follows: (1) semi-cylindrical section enveloped in a 5-mm adipose layer; (2) semi-elliptical section with a 4-mm thick skin; (3) semi-cylindrical section with a 1.45-mm skin layer; (4) semi-cylindrical section in a 1.45-mm skin layer and 2-mm subcutaneous adipose layer. Twenty patient specific digital breast phantoms produced from a dedicated CT scanner were assumed as reference in the comparison. We simulated two spectra produced from two anode/filter combinations. An additional digital breast phantom was produced via BreastSimulator software. Results: With reference to the results for patient-specific breast phantoms and for W/Al spectra, models #1 and #3 showed higher MGD values by about 1% (ranges [–33%; +28%] and [−31%; +30%], respectively), while for model #4 it was 2% lower (range [−34%; +26%]) and for model #2 –11% (range [−39%; +14%]), on average. On the other hand, for W/Rh spectra, models #1 and #4 showed lower MGD values by 2% and 1%, while for model #2 and #3 it was 14% and 8% lower, respectively (ranges [−43%; +13%] and [−41%; +21%]). The simulation with the digital breast phantom produced with BreastSimulator showed a MGD overestimation of +33%. Conclusions: The homogeneous breast models led to maximum MGD underestimation and overestimation of 43% and 28%, respectively, when compared to patient specific breast phantoms derived from clinical CT scans.

3D breast modelling for 2D and 3D breast x-ray imaging would benefit from the availability of digital and physical phantoms that reproduce accurately the complexity of the breast anatomy. While a number of groups have produced digital phantoms with increasing level of complexity, physical phantoms reproducing that software approach have been scarcely developed. One possibility is offered by 3D printing technology. This implies the assessment of the energy dependent absorption index β of 3D printing materials for absorption based imaging, as well as the assessment of the refractive index decrement, δ, of the printing material, for phase contrast imaging studies, at the energies of interest for breast imaging. In this work we set-up a procedure and performed a series of measurements (at 30, 45 and 60 keV, at the European Synchrotron Radiation Facility) for assessing the relative value of δ with respect to that of breast tissues, for twelve 3D printing materials. The method included propagation based phase contrast 2D imaging and retrieval of the estimated phase shift map, using the Paganin's algorithm. Breast glandular, adipose and skin tissues were used as reference materials of known ratio δ/β. A percentage difference Δδ was introduced to assess the suitability of the printing materials as tissue substitutes. The accuracy of the method (about 4%) was assessed based on the properties of PMMA and Nylon, acting as gold standard. Results show that, for the above photon energies, ABS is a good substitute for adipose tissue, Hybrid as a substitute of the glandular tissue and PET-G for simulating the skin. We plan to realize a breast phantom manufactured by fused deposition modelling (FDM) technology using ABS, Hybrid and PET-G as substitutes of the glandular and skin tissue and a second phantom by stereolithography (SLA) technology with the resins Flex, Tough and Black.

Purpose We investigated the feasibility of kilovoltage rotational radiotherapy for breast cancer (kV-EBRT) via Monte Carlo simulations and measurements on phantoms. Methods We derived the dose distributions for X-ray beams at 150 kV, 300 kVp and 320 kV irradiating breast cylindrical phantoms of 14 cm diameter, mimicking the pendant breast. Simulations were based on the Geant4 toolkit. The point-like X-ray source was rotated either over a full circle or on a limited arc around the phantom. We studied the influence on the surface dose of the distance between the tumor lesion to the skin, of the irradiation protocol (full scan or partial scan) and of the X-ray tube current modulation. Results Rotational kV-EBRT permitted a periphery-to-center dose ratio from 13% to 9% in homogeneous breast phantoms. Dose distributions in phantoms with off-center simulated lesions, showed a skin-to-tumor dose ratio of 16% and 34% for lesions at 3.25 and 5.25 cm from cylinder axis, respectively. Simulation of the X-ray tube current modulation during the rotation, permits to reach a dose ratio of 20% for the lesion located at 5.25 cm from phantom axis. Conclusions We showed the possibility of using low-energy X-ray spectra for kV-EBRT with collimated beams, for obtaining a periphery-to-center dose ratio in the same order of conventional accelerator based megavoltage radiotherapy, when the irradiated area is localized in the center of the breast. For tumors localized near the breast border, we showed that the tube current modulation can be a good solution in order to reduce the skin-to-tumor dose ratio.

Purpose: To provide mean glandular dose (MGD) estimates via Monte Carlo (MC) simulations as a function of the breast models and scan parameters in mammography, digital breast tomosynthesis (DBT) and dedicated breast CT (BCT). Methods: The MC code was based on GEANT4 toolkit. The simulated compressed breast was either a cylinder with a semi-circular section or ad hoc shaped for oblique view (MLO). In DBT we studied the influence of breast models and exam parameters on the T-factors (i.e. the conversion factor for the calculation of the MGD in DBT from that for a 0-degree projection), and in BCT we investigated the influence on the MGD estimates of the ion chamber volume used for the air kerma measurements. Results: In mammography, a model representative of a breast undergoing an MLO view exam did not produce substantial differences (0.4%) in MGD estimates, when compared to a conventional cranio-caudal (CC) view breast model. The beam half value layer did not present a significant influence on T-factors in DBT (< 0.8%), while the skin model presented significant influence on MGD estimates (up to 3.3% at 30 degrees scan angle), increasing for larger scan angles. We derived a correction factor for taking into account the different ion chamber volume used in MGD estimates in BCT. Conclusions: A series of MC code modules for MGD estimates in 2D and 3D breast imaging have been developed in order to take into account the most recent advances in breast models.

Purpose: This work investigates the energy response and dose-response curve determinations for XR-QA2 radiochromic film dosimetry system used for synchrotron radiation work and for quality assurance in diagnostic radiology, in the range of effective energies 18–46.5 keV. Methods: Pieces of XR-QA2 films were irradiated, in a plane transverse to the beam axis, with a monochromatic beam of energy in the range 18–40 keV at the ELETTRA synchrotron radiation facility (Trieste, Italy) and with a polychromatic beam from a laboratory x-ray tube operated at 80, 100, and 120 kV. The film calibration curve was expressed as air kerma (measured free-in-air with an ionization chamber) versus the net optical reflectance change (netΔR) derived from the red channel of the RGB scanned film image. Four functional relationships (rational, linear exponential, power, and logarithm) were tested to evaluate the best curve for fitting the calibration data. The adequacy of the various fitting functions was tested by using the uncertainty analysis and by assessing the average of the absolute air kerma error calculated as the difference between calculated and delivered air kerma. The sensitivity of the film was evaluated as the ratio of the change in net reflectance to the corresponding air kerma. Results: The sensitivity of XR-QA2 films increased in the energy range 18–39 keV, with a maximum variation of about 170%, and decreased in the energy range 38–46.5 keV. The present results confirmed and extended previous findings by this and other groups, as regards the dose response of the radiochromic film XR-QA2 to monochromatic and polychromatic x-ray beams, respectively. Conclusions: The XR-QA2 radiochromic film response showed a strong dependence on beam energy for both monochromatic and polychromatic beams in the range of half value layer values from 0.55 to 6.1 mm Al and corresponding effective energies from 18 to 46.5 keV. In this range, the film response varied by 170%, from a minimum sensitivity of 0.0127 to a maximum sensitivity of 0.0219 at 10 mGy air kerma in air. The more suitable function for air kerma calibration of the XR-QA2 radiochromic film was the power function. A significant batch-to-batch variation, up to 55%, in film response at 120 kV (46.5 keV effective energy) was observed in comparison with published data.

The purpose of this work is to provide an evaluation of the mean glandular dose (MGD) for breast computed tomography (CT) with synchrotron radiation in an axial scanning configuration with a partial or total organ volume irradiation, for the in vivo program of breast CT ongoing at the ELETTRA facility (Trieste, Italy). A Geant4 Monte Carlo code was implemented, simulating the photon irradiation from a synchrotron radiation source in the energetic range from 8 to 50 keV with 1 keV intervals, to evaluate the MGD. The code was validated with literature data, in terms of mammographic normalized glandular dose coefficients (DgN) and with ad hoc experimental data, in terms of computed tomography dose index (CTDI). Simulated cylindrical phantoms of different sizes (diameter at phantom base 8, 10, 12, 14 or 16 cm, axial length 1.5 times the radius) and glandular fraction by weight (0%, 14.3%, 25%, 50%, 75% and 100%) were implemented into the code. The validation of the code shows an excellent agreement both with previously published work and in terms of DgN and CDTI measurements. The implemented simulations show a dependence of the glandular dose estimate on the vertical dimension of the irradiated zone when a partial organ irradiation was implemented. Specific normalized coefficients for calculating the MGD to the whole breast or to the single irradiated slice were reported.

Contains fulltext : 181906.pdf (Publisher’s version ) (Open Access) The aim of this work is the evaluation of the software BreastSimulator, a breast X-ray imaging simulation software as a tool for the creation of 3D uncompressed breast digital models and for the simulation and the optimization of computed tomographic (CT) scanners dedicated to the breast. Eight 3D digital breast phantoms were created with glandular fraction in the range 10% to 68%. The models are characterised by different sizes and modelled realistic anatomical features.. X-ray CT projections were simulated for a dedicated cone-beam CT scanner and reconstructed with the FDK algorithm. X-ray projection images were simulated for 5 mono-energetic (27, 32, 35, 43 and 51 keV) and 3 poly-energetic X-ray spectra typically employed in current CT scanners dedicated to the breast (49, 60, or 80 kVp). Clinical BCT images acquired from two different clinical breast CT scanners were used for comparison purposes. The quantitative evaluation included calculation of the power-law exponent, beta, from simulated and real breast tomograms, based on the Noise Power Spectrum (NPS) fitted with a function S(f) = alpha/fbeta. The breast models were validated by comparison against clinical breast CT and published data. The calculated beta coefficients are close to that of clinical CT data from a dedicated breast CT scanner and reported data in the literature.In this paper we evaluated the software package BreastSimulator to generate breast models suitable for use with breast CT imaging The breast phantoms produced with the software tool can reproduce the anatomical structure of real breasts, as evaluated by calculating the beta exponent from the power spectral analysis of simulated images. As such, this research tool will contribute considerably to the further development, testing and optimisation of breast CT imaging technique.

Purpose To investigate depth-dose characteristics of a new technique for orthovoltage rotational breast radiotherapy (RT) via Monte Carlo (MC) simulations and experimental phantom study, following the initial work by Boone [1] . Methods Geant4 MC simulations were developed to calculate dose distributions generated by an orthovoltage (320 kVp, 4 mm Cu filtration) or kilovoltage (150 kV, 1 mm Cu) X-ray beams rotating 360° around a cylindrical phantom (polyethylene or PMMA) placed at isocentre to simulate prone patient’s breast. Horizontal beam collimation was 1–14 cm. Radial and longitudinal depth-dose distributions were performed for homogeneous phantoms (with or without lesions simulated for different depths in phantom). Experimental validation was performed on the same geometry with the 150 kV beam. Farmer-type air ionization chamber and radiochromic films are used to measure radial dose profiles. Results MC simulations at 320 kVp show that rotational kilovoltage radiotherapy assures sufficient skin sparing during breast RT. Centre to periphery dose ratio is less than 20:1 (1 cm collimation in the horizontal plane at 320 kVp). The vertical dose spread profile shows limited influence of the scatter dose at distance of 10 mm from the irradiated slice. MC simulations will be compared to laboratory measurements at 150 kV. Conclusions We showed the potential of orthovoltage external beam rotational RT for breast cancer with satisfactory skin sparing, though using a kilovoltage beam.

The response of LiF:Mg,Cu,P thermoluminescence dosemeters (type GR-200A) to monoenergetic radiation of energy 28, 35, 38 and 40 keV was evaluated with respect to irradiation with a calibrated (60)Co gamma-ray source. High-precision measurements of the relative air kerma response performed at the SYRMEP beamline of the ELETTRA synchrotron radiation facility (Trieste, Italy) showed a significant deviation of the average response to low-energy X-rays from that to (60)Co, with an over-response from 6 % (at 28 keV) to 22 % (at 40 keV). These data are not consistent with literature data for these dosemeters, where model predictions gave deviation from unity of the relative air kerma response of about 10 %. The authors conclude for the need of additional determinations of the low-energy relative response of GR-200A dosemeters, covering a wider range of monoenergetic energies sampled at a fine energy step, as planned in future experiments by their group at the ELETTRA facility.

We present the implementation of the CT iterative reconstruction strategy developed within the SYRMA-CT project for in vivo phase contrast CT of the uncompressed breast, ongoing at the ELETTRA synchrotron radiation facility (Trieste, Italy). Propagation-based phase-contrast imaging exploited the high spatial coherence of the monoenergetic laminar X-ray beam (3-mm high along the chest-wall-to-nipple direction), as well as the large object-to-detector distance (∼2 m) and the use of a prototype of Pixirad-8 high-resolution photon counting CdTe detector (60-μm pitch, eight detector units arranged in a row). The signal in projection views depends on the X-ray absorption as well as on the phase shift introduced by the breast tissue in the beam path. A phase retrieval algorithm allows recovering the projected 2D phase map of the irradiated tissue layer, which were input to the CT reconstruction; then, the 3D image of the breast was reconstructed via a simultaneous algebraic reconstruction technique (SART) algorithm. The developed iterative reconstruction — coupled with a filtering process for reducing the noise level and ring artifacts by preserving edges sharpness — showed better image quality than conventional filtered backprojection (FBP) reconstruction. A phantom study showed that the iterative reconstruction produced images with a contrast-to-noise-ratio up to 65% and a spatial resolution up to 12% higher than those obtained with FBP. Finally, the developed algorithm removed ring-like artifacts caused by the detector dead space (0.16 mm) across adjacent detector units and by no perfect equalization after flat-field correction, without worsening the image quality.

The SYRMA-CT project aims to set-up the first clinical trial of phase-contrast breast Computed Tomography with synchrotron radiation at the SYRMEP beamline of Elettra, the Italian synchrotron light source. The challenge in a dedicated breast CT is to match a high spatial resolution with a low dose level. In order to fulfil these requirements, the SYRMA-CT project uses a large area CdTe single photon counting detector (Pixirad-8), simultaneous algebraic reconstruction technique (SART) and phase retrieval pre-processing. This work investigates the imaging performances of the system in a continuous acquisition mode and with a low dose level towards the clinical application. A custom test object and a large surgical sample have been studied.

In Monte Carlo simulations for estimation of normalized glandular dose coefficients (i.e. the ratio between the mean glandular dose (MGD) and incident air kerma at the breast upper surface), the radiosensitive breast tissue is modelled as a homogeneous mixture of adipose and glandular tissue. However, such an assumption has been shown to lead to an overestimation in MGD by an average of 30% [1] , [2] . This work aimed at comparing the homogeneous breast models proposed by different authors and in different quality assurance protocols to patient specific breast phantoms. To obtain these phantoms, uncompressed breast images were acquired with a CT scanner dedicated to the breast and segmented to classify each voxel into 4 categories: air, skin tissue, adipose tissue and glandular tissue. Then the compression which breasts undergo during a mammography exams was simulated via software in order to obtain 3D compressed patient specific breast phantoms which present an heterogeneous glandular distribution similar to that of the irradiated breast. The homogeneous breast phantom was simulated either with a 4-mm skin thickness (as adopted in the USA protocol), or with a 5-mm adipose layer simulating the skin and the subcutaneous adipose layer (as adopted in the EU protocol) or with a skin thickness of 1.45 mm (i.e. the skin thickness estimated from 3D breast images). A pre-validated Monte Carlo code based on GEANT4 toolkit ver. 10.00 [3] was employed to calculate the dose differences between the standard models and the patient specific breast phantom. This study provided an insight into possible bias of the standard models for breast dosimetry and an indication of new breast model for future normalized glandular dose calculations.

The mean radiation dose to the glandular tissue and its dependence on the irradiation geometry, beam quality, breast size and composition in digital breast tomosynthesis (DBT) exams have been studied extensively via Monte Carlo calculations [1] . On the other hand, there are few comprehensive studies on the dose distribution within the irradiated breast [2] . The distribution of glandular dose for breast irradiation from a plurality of angles, as occurs in DBT, may be of large interest in scanner optimization as well as for developing suitable models for the evaluation of the cancer risk related to the X-ray exposure for non–homogeneous irradiation. For this reason, it is of interest to evaluate the level of homogeneity of the dose spread, via the assessment of 3D dose maps in breast models during a DBT scan. This work aimed at evaluating, via Monte Carlo (MC) simulations and measurements using radiochromic films, the dose distribution within compressed layered breast phantoms during DBT scans. For this purpose, two phantoms were employed: a PMMA homogeneous phantom and a heterogeneous phantom simulating a 50% glandular breast. A series of pre-calibrated (vs free-in-air air kerma) film pieces were inserted between the phantom slices and the 3D dose maps were measured for a set of DBT scans on different commercial units, for different sample thicknesses, at various exposure technique factors. We developed an MC code based on GEANT4 toolkit ver. 10.00, simulating the clinical setup specifications, whose results have been compared to measurements. This project received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 692097 for the MaXIMA project: Three dimensional breast cancer models for X-ray imaging research.

Purpose To measure the dose distribution in a phantom during a synchrotron radiation (SR) computed tomography (CT) scan using radiochromic films, for procedure assessment and for offline dose monitoring in SR breast CT. Methods We used XR-QA2 radiochromic films (calibrated in terms of free air kerma) and a 14-cm PMMA cylindrical phantom. Measurements were performed at the SYRMEP beamline of ELETTRA facility, within the SYRMA-3D project for phase-contrast breast CT [1] . The phantom was positioned at isocenter, pending from the patient bed. Measurements were performed at 38 keV, beam size of 3 mm × 150 mm (H × W), at an air kerma corresponding to a mean glandular dose of 5 mGy in a 14-cm diameter 50% glandular breast. The phantom was irradiated over 360° first with a film at the mid-plane, and then with film strips wrapped on its surface. Additional tests were made over 180° with an axial scan pitch of 1, 0.8 or 0.5. Results Results show a dose map at mid-plane the phantom, indicating the cup-shaped horizontal profile due to primary and scatter dose. Analogous maps were recorded with the films at the periphery of the phantom, representing the surface dose maps. Conclusions We performed measurements of the dose distribution in a phantom during a SR CT scan with different irradiation geometries. This technique produces evidence for selecting the suitable scan procedure. Moreover, as an offline monitor system, a piece of calibrated radiochromic film wrapped on a suitable holder around the breast could record the history of the organ irradiation.

Purpose We proposed a new technique for breast cancer rotational radiotherapy using kilovoltage synchrotron radiation (SR) [1] . Here, we compared 2D dose distributions in a breast phantom at 6 MV in circular orbit Volumetric Arc Therapy (VMAT) with respect to 100 keV irradiation in rotational radiotherapy with SR. Methods The dose distribution was evaluated with calibrated EBT3 radiochromic films inserted at midplane in a 14-cm diameter PMMA cylindrical phantom, simulating the pendant breast. We irradiated a cylindrical target (15 × 20 mm2 (W × H)) at the centre of phantom. Measurements were performed at the Imaging and Medical Beamline (Australian Synchrotron, Clayton, Australia) at 100 keV, with a SR beam of size 15 × 20 mm2 (W × H) continuously irradiating the phantom during a 360 deg rotation around the cylinder axis with a central dose to the target of 7 Gy. Megavoltage measurements were performed at 6 MV using a Varian Clinac iX System Linac, with a target dose of 6 Gy. Results The principle of dose summation along the axis of rotation produced a dose distribution peaked at the centre of rotation for small fields. The target-to-surface dose ratio was 20:1 at 6 MV and 9:1 at 100 keV, for a target at the center of the phantom. Conclusions We performed a feasibility test of kilovoltage rotational radiotherapy dedicated to the breast showing a target-to-surface dose ratio higher than with MV radiotherapy but still acceptable for skin tissue sparing.

Purpose To compute, via GEANT4 based Monte Carlo (MC) simulations, normalized glandular dose (DgN) coefficients for mean glandular dose (MGD) estimates in 2D and 3D X-ray breast imaging. Methods We developed a Monte Carlo code for DgN calculation (MGD/air kerma, mGy/mGy) in mammography, digital breast tomosynthesis (DBT) and breast CT. The code is based on GEANT4 toolkit ver. 10.00 with the low-energy physics list Option4, and it was validated vs. data from the AAPM-TG195 report and vs. measurements. The geometry of the available scanners were replicated and the breast was modelled as a cylinder with a semi-circular cross section (in mammography and DBT), and as a pendant cylinder in breast CT. The skin thickness was 1.45 mm. The MC simulations were run for monoenergetic beams in the energy range usually adopted in clinic and research. The monoenergetic DgN curves were fitted with 8th-order polynomial curves, and then the polyenergetic DgN coefficients were calculated. Results We obtained a full set of monoenergetic DgN coefficients for mammography, DBT and breast CT. The monoenergetic DgN fitting curves showed a fitting R2 higher than 0.9998. The polyenergetic DgN coefficients were computed for a large cohort of spectra used in the routine clinical practice. The data were comparable with those present in literature. Conclusions A validated MC code for DgN estimates in 2D and 3D X-ray breast imaging has been presented. A breast model has been defined. Monoenergetic and polyenergetic DgN coefficients have been computed. A complete dataset containing monoenergetic DgN curve fit coefficients and polyenergetic DgN coefficients have been released. DgN differed, on average, 6% and 13%, in mammography and breast CT, respectively, from literature data in Refs. [1] , [2] .

The aim of the SYRMA-CT collaboration is to set-up the first clinical trial of phase-contrast breast CT with synchrotron radiation (SR). In order to combine high image quality and low delivered dose a number of innovative elements are merged: a CdTe single photon counting detector, state-of-theart CT reconstruction and phase retrieval algorithms. To facilitate an accurate exam optimization, a Monte Carlo model was developed for dose calculation using GEANT4. In this study, high isotropic spatial resolution (120 mu m)(3) CT scans of objects with dimensions and attenuation similar to a human breast were acquired, delivering mean glandular doses in the range of those delivered in clinical breast CT (5-25 mGy). Due to the spatial coherence of the SR beam and the long distance between sample and detector, the images contain, not only absorption, but also phase information from the samples. The application of a phase-retrieval procedure increases the contrast-to-noise ratio of the tomographic images, while the contrast remains almost constant. After applying the simultaneous algebraic reconstruction technique to low-dose phase-retrieved data sets (about 5 mGy) with a reduced number of projections, the spatial resolution was found to be equal to filtered back projection utilizing a four fold higher dose, while the contrast-to-noise ratio was reduced by 30%. These first results indicate the feasibility of clinical breast CT with SR.

Introduction The first clinical trial of phase-contrast mammography with monochromatic beam was performed at Elettra, the Italian Synchrotron Radiation facility. A lower Mean Glandular Dose (MGD) and a higher specificity were achieved compared to the digital mammography for the patient cohort (more than 70). Purpose The SYRMA-CT project (SYnchrotron Radiation for MAmmography – Computed Tomography) aims to perform the first clinical trial of phase-sensitive breast CT with monochromatic beam. High image quality and low dose are expected according to the results of the first mammography trial. Materials and methods A large area CdTe single photon counting detector (PIXIRAD-8) is used. Phase-retrieval algorithm are applied, thus exploiting propagation based phase-contrast imaging (PPCI). The dose system of the beamline has been calibrated to match the energy requirement up to 40 keV. Due to the peculiar irradiation modality, ad hoc Monte Carlo simulations and experimental measurements were performed for dose evaluation. Results Images of surgical samples included in large test objects (up to 12 cm diameter) were acquired at 38 keV in clinical compatible dose conditions (MGD ∼5 mGy). Phase-retrieval pre-processing was applied improving the CNR of the high-resolution images with (120 μm) 3 voxel size. Conclusion The upgrade of the mammographic facility of the Elettra laboratory towards a new clinical trial is going on. Image quality and dose assessment indicate its feasibility with monochromatic beam. This clinical trial will allow the evaluation of PPCI breast CT in optimal conditions and will give indication for the translation to the hospital of phase-sensitive techniques. Disclosure Nothing to declare.

Purpose Within the SYRMA-CT collaboration based at the ELETTRA synchrotron radiation (SR) facility the authors investigated the imaging performance of the phase-contrast computed tomography (CT) system dedicated to monochromatic in vivo 3D imaging of the female breast, for breast cancer diagnosis. Methods Test objects were imaged at 38 keV using monochromatic SR and a high-resolution CdTe photon-counting detector. Signal and noise performance were evaluated using modulation transfer function (MTF) and noise power spectrum. The analysis was performed on the images obtained with the application of a phase retrieval algorithm as well as on those obtained without phase retrieval. The contrast to noise ratio (CNR) and the capability of detecting test microcalcification clusters and soft masses were investigated. Results For a voxel size of (60 μm)3, images without phase retrieval showed higher spatial resolution (6.7 mm−1 at 10% MTF) than corresponding images with phase retrieval (2.5 mm−1). Phase retrieval produced a reduction of the noise level and an increase of the CNR by more than one order of magnitude, compared to raw phase-contrast images. Microcalcifications with a diameter down to 130 μm could be detected in both types of images. Conclusions The investigation on test objects indicates that breast CT with a monochromatic SR source is technically feasible in terms of spatial resolution, image noise and contrast, for in vivo 3D imaging with a dose comparable to that of two-view mammography. Images obtained with the phase retrieval algorithm showed the best performance in the trade-off between spatial resolution and image noise.

Introduction: The authors characterized the response of EBT3 radiochromic films to proton and carbon ion beams. EBT3 films are adopted routinely for dosimetry and for QA at linear accelerators used for conventional radiotherapy, and for QA in hadrontherapy. In contrast to sparsely ionizing radiations, irradiation by ions leads to a strongly inhomogeneous dose deposition. A quenching effect occurs in the film response consisting of an under-response of the EBT3 to ion beams with respect to MV-photon beams, likely due to the ion track structure. The authors investigated the response of EBT3 films to proton and carbon ion beams, and compared it with photon and electron beams' response, for assessment of a dose–response correction procedure. Method and materials: The EBT3 films were calibrated in the dose range of 0.4–20 Gy with proton (63, 150 and 230 MeV) and carbon ion (115 MeV/u and 400 MeV/u) beams as well as to radiotherapy photon (6, 18 MV and 60 Co) and electron (6 and 12 MeV) beams. The measurements were performed at ‘National Center for Oncological Hadrontherapy’ (CNAO Pavia, Italy) for proton and carbon ion beams and at ‘San Raffaele Hospital’ (HSR Milan, Italy) for photon and electron beams. Results: The dose–response curves were fitted to a quadratic-like function with a relative error of less than 3%. The EBT3 response to protons was found to be very similar to the response of photon and electron beams and no saturation occurred. The relative response of carbon ions was less than unity for all dose values and lower for low-energy ions. The carbon ion curves show an under-response, up to 25% for the lower investigated energy, in comparison with photon and electron curves. Conclusions: For proton beams, at all energies, the dose–response curves are statistically not different from photon and electron curves. For carbon ions an under-response was observed which is higher for lower energy (higher LET) beams

External beam rotational radiotherapy of breast cancer with kilovoltage photons (kV-EBRT), with the patient in prone position, has been proposed [1] as a possible alternative to conventional radiotherapy with two tangential 6-MV X-ray beams produced by a medical linac with a supine patient. kV-EBRT uses a dedicated setup initially developed for breast CT, with a 320-kVp beam from an orthovoltage X-ray tube rotating in full circles around the breast; CT for tumour localization can be performed by using the same setup. Though dose build-up is not present, rotational summation of dose delivery allows a skin sparing comparable to conventional radiotherapy. We proposed the use of a monoenergetic synchrotron radiation (SR) collimated beam for image-guided rotational radiotherapy for the pendant breast (SR3T) [2] . The high flux of SR permits dose rates even greater to that of conventional radiotherapy, while the optimal photon energy can be selected for the treatment. In this work, we present Monte Carlo simulation and a simple model for evaluation of the 3D dose distribution in SR3T. The MC code was based on GEANT4 toolkit ver.10.00. We validated these simulations via measurements on breast phantoms performed at the Imaging and Medical Beamline of the Australian Synchrotron. We measured the dose distribution in cylindrical PMMA and polyethylene phantoms at 60 keV, using an ionization chamber, thermoluminescent dosimeters and radiochromic films. This study indicated that for a tumour localized at the centre of a mid-sized breast (14-cm diameter at chest wall), a ”skin-to-tumour” dose ratio of 14% can be reached at 60 keV with a collimated SR beam. Non uniform dose distribution to the target (dose painting) can be performed with multiple rotations around the organ. Kilovoltage SR3T with suitable radiosensitizers may exploit the dose enhancement factor due to increased photoelectric absorption, at SR beam energies in the 60–110 keV range.

This work aimed at calculating the complete set of monoenergetic (DgN) and polyenergetic (DgNp) normalized glandular dose coefficients for mean glandular dose estimate in mammography. We have developed a Monte Carlo code based on GEANT4 toolkit, for DgN calculation, which relies on the standard physics list Option4. Influence of the breast model, the compression paddle and the bremsstrahlung process on DgN and DgNp normalized glandular dose coefficients in mammography was studied. Breast skin thickness was varied in the range 1.45–5 mm. It was modeled both as an adipose skin layer (5 mm thick – as in EU protocols for mammography) and as a real skin composition (as adopted in USA protocols). Significant differences in the calculated DgN have been observed when 1.45 mm skin thickness is adopted. At 15 keV a skin thickness of 1.45 mm produces values up to 25% or 20% higher than in the model adopted in the USA (4 mm skin) or EU protocol (5 mm adipose layer), respectively. The discrepancy reduces for higher energies. For routinely used mammographic spectra, a skin thickness of 4 mm produces DgNp values up to 32% lower than those with a breast model with 1.45 mm thickness. The bremsstrahlung processes in the breast tissue had small influence on DgN coefficients. Finally, based on the model consideration, DgNp coefficients for spectra used in mammography were provided and compared with those routinely adopted, based on USA and EU protocols.

A few groups have developed cone-beam breast computed tomography scanners dedicated to the breast (BCT) [1] , for breast cancer diagnosis. BCT is a 3D X-ray imaging technique, which aims at reducing the presence of the anatomical noise in X-ray breast images, due to the superposition of breast structures and tissues. The common metric for breast radiation dosimetry in BCT is the Mean Glandular Dose (MGD), i.e. the average absorbed dose in the glandular component of the breast tissue. The MGD is estimated on the basis of air kerma measurements, and normalized glandular dose coefficients (DgN) evaluated via Monte Carlo (MC) simulations [2] . In such a context, the breast is modeled as a homogenous mixture of glandular and adipose tissue embodied in a skin layer. We evaluated the DgN in BCT by modeling the breast as a heterogeneous mixture of adipose and glandular tissues. We realized an MC code based on GEANT4 toolkit simulating the acquisition setup and considering the interactions included in the standard electro-magnetic libraries. The MC code was previously validated vs. data from the AAPM Task Group 195, as well as vs. measured data. The dose was scored in locations inside a grid of cubic voxels designed using patient BCT scans provided by University of California Davis. The voxels were classified in adipose tissue, glandular tissue, skin tissue or air via an opportune segmentation algorithm. Such a voxellized phantom, with a real glandular distribution, was input in the MC code for estimating the MGD. This post-exam estimate was compared with the corresponding estimate evaluated before the exam using a homogeneous tissue mixture approximation. This project received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 692097 for the MaXIMA project: Three dimensional breast cancer models for X-ray imaging research.

This work investigates the use of XR-QA2 radiochromic films for quantitative imaging of a synchrotron radiation (SR) beam. Pieces (200 × 30 mm2) of XR-QA2 film were irradiated in a plane transverse to the beam axis, at the SYRMEP beamline at ELETTRA (Trieste), with a monochromatic beam of size 170 × 3.94 mm2 (H × V) and energy of 28, 35, 38 or 40 keV. The response was calibrated in terms of average air kerma (120 mGy), measured with a calibrated ionization chamber. Films were digitized in reflectance mode using a flatbed scanner. The 16-bit red channel was used. The netreflectance was then converted to photon fluence per unit air kerma (mm-2 mGy-1). The SR beam profile was acquired also with a scintillator (GOS) based, fiberoptic coupled CCD camera as well as with a scintillator based flat panel detector. Horizontal profiles obtained with the two modalities were compared, evaluated in a ROI of 17.71 × 0.59 mm2, across the beam centre. Once corrected for flat field, the CCD profile was scaled in order to have the same average value as the normalized profile acquired with the gafchromic film. The same procedure was followed for the beam images acquired with the flat panel detector. Horizontal and vertical line profiles acquired with the radiochromic film show an uneven 2D distribution of the beam intensity, with variations in the order of 1520% in the horizontal direction, while the statistical uncertainties evaluated for the radiochromic dose measurements were 6% at 28 keV. Larger variations up to 64% were observed in the vertical direction. The response of the radiochromic film is comparable to that of the other imaging detectors, within less than 5% variation.