Expected and paradoxical effects of obesity on cancer treatment response.

Obesity, whose prevalence is pandemic and continuing to increase, is a major preventable and modifiable risk factor for diabetes and cardiovascular diseases, as well as for cancer. Furthermore, epidemiological studies have shown that obesity is a negative independent prognostic factor for several oncological outcomes, including overall and cancer-specific survival, for several site-specific cancers as well as for all cancers combined. Yet, a recently growing body of evidence suggests that sometimes overweight and obesity may associate with better outcomes, and that immunotherapy may show improved response among obese patients compared with patients with a normal weight. The so-called 'obesity paradox' has been reported in several advanced cancer as well as in other diseases, albeit the mechanisms behind this unexpected relationship are still not clear. Aim of this review is to explore the expected as well as the paradoxical relationship between obesity and cancer prognosis, with a particular emphasis on the effects of cancer therapies in obese people.

Real-time algorithm for Poissonian noise reduction in low-dose fluoroscopy: performance evaluation.

BACKGROUND: Quantum noise intrinsically limits the quality of fluoroscopic images. The lower is the X-ray dose the higher is the noise. Fluoroscopy video processing can enhance image quality and allows further patient's dose lowering. This study aims to assess the performances achieved by a Noise Variance Conditioned Average (NVCA) spatio-temporal filter for real-time denoising of fluoroscopic sequences. The filter is specifically designed for quantum noise suppression and edge preservation. It is an average filter that excludes neighborhood pixel values exceeding noise statistic limits, by means of a threshold which depends on the local noise standard deviation, to preserve the image spatial resolution. The performances were evaluated in terms of contrast-to-noise-ratio (CNR) increment, image blurring (full width of the half maximum of the line spread function) and computational time. The NVCA filter performances were compared to those achieved by simple moving average filters and the state-of-the-art video denoising block matching-4D (VBM4D) algorithm. The influence of the NVCA filter size and threshold on the final image quality was evaluated too. RESULTS: For NVCA filter mask size of 5 × 5 × 5 pixels (the third dimension represents the temporal extent of the filter) and a threshold level equal to 2 times the local noise standard deviation, the NVCA filter achieved a 10% increase of the CNR with respect to the unfiltered sequence, while the VBM4D achieved a 14% increase. In the case of NVCA, the edge blurring did not depend on the speed of the moving objects; on the other hand, the spatial resolution worsened of about 2.2 times by doubling the objects speed with VBM4D. The NVCA mask size and the local noise-threshold level are critical for final image quality. The computational time of the NVCA filter was found to be just few percentages of that required for the VBM4D filter. CONCLUSIONS: The NVCA filter obtained a better image quality compared to simple moving average filters, and a lower but comparable quality when compared with the VBM4D filter. The NVCA filter showed to preserve edge sharpness, in particular in the case of moving objects (performing even better than VBM4D). The simplicity of the NVCA filter and its low computational burden make this filter suitable for real-time video processing and its hardware implementation is ready to be included in future fluoroscopy devices, offering further lowering of patient's X-ray dose.

Role of contrast-enhanced ultrasound to define prognosis and predict response to biotherapy in pancreatic neuroendocrine tumors.

PURPOSE: The incidence of neuroendocrine tumors (NETs) is progressively increasing. Most cases arise from the digestive system, where ileum, rectum and pancreas represent the commonest site of origin. Liver metastases are frequently detected at diagnosis or during the follow-up. Contrast-enhanced ultrasound (CEUS) is used in patients with pancreatic NETs (P-NETs) and liver metastases from P-NET but its role has not been standardized. The aim of this retrospective study was to investigate CEUS in patients with P-NETs and liver metastases from P-NET both as prognostic factor and predictor of response to therapy with somatostatin analogues (SSAs). METHODS: CEUS was performed at the diagnosis of NET and 3, 6 and 12 months after the beginning of SSAs. CEUS pattern was compared with contrast-enhanced computed tomography (CT) pattern. RESULTS: There was a significant association between CEUS and CT pattern (X 2 = 79.0; p < 0.0001). A significant association was found between CEUS pattern and Ki-67 index (X 2 = 24.6; p < 0.0001). The hypervascular homogeneous CEUS typical pattern was associated with low tumor grading (G1 or G2) (X 2 = 24.0; p < 0.0001). CEUS pattern changed from hypervascular homogeneous in baseline to hypovascular/hypervascular inhomogeneous after SSA therapy, with a significant association between tumor response at CT scan and appearance of hypervascular inhomogeneous pattern at CEUS evaluation (6 months: X 2 = 57.0; p < 0.0001; 12 months: X 2 = 49.8; p < 0.0001). CONCLUSIONS: In patients with P-NET, CEUS pattern correlates with tumor grading, being homogeneous in G1-G2 but not in G3 tumors. After therapy with SSAs, CEUS is predictive of response to SSAs. These findings seem to support a role of CEUS as prognostic and predictive factor of response.

Impact of long-acting octreotide in patients with early-stage MEN1-related duodeno-pancreatic neuroendocrine tumours.

BACKGROUND: Somatostatin analogues (SSA) represent one of the main therapeutic option in patients affected with functioning well-differentiated neuroendocrine tumours (NETs). There are no studies specifically focusing on NETs associated with Multiple Endocrine Neoplasia type 1 (MEN1). AIM: To evaluate the efficacy of the long-acting SSA octreotide in MEN1 patients with early-stage duodeno-pancreatic NETs. PATIENTS AND METHODS: Forty patients with MEN1 were retrospectively evaluated. Twenty patients with evidence of one or more MEN1-related duodeno-pancreatic NETs < 20 mm in size (age range 26-61 years) were treated with octreotide long-acting octreotide (LAR) as first-line therapy. Treatment duration ranged 12-75 months. At the baseline radiological evaluation, multiple duodeno-pancreatic NETs (range 1-8, size 3-18 mm) were detected. RESULTS: An objective tumour response was observed in 10%, stable disease in 80% and progression of disease in 10% of cases. In six patients with abnormally increased CgA, gastrin and/or insulin serum concentrations, a significant clinical and hormonal response occurred in 100% of cases and was stable along the time. CONCLUSIONS: Therapy with SSA is highly safe and effective in patients with early-stage MEN1 duodeno-pancreatic NETs, resulting in long-time suppression of tumour and hormonal activity and 10% objective response. This suggests to early start therapy with SSA in patients with MEN1-related NETs.

A new schedule of one week on/one week off temozolomide as second-line treatment of advanced neuroendocrine carcinomas (TENEC-TRIAL): a multicenter, open-label, single-arm, phase II trial.

BACKGROUND: There is no consensus on the second-line treatment of patients with progressive high-grade neuroendocrine neoplasms (NENs G3) and large-cell lung neuroendocrine carcinoma. These patients generally have poor performance status and low tolerance to combination therapy. In this trial, we aim to evaluate the efficacy and safety of temozolomide given every other week in patients with advanced platinum-pretreated NENs G3. PATIENTS AND METHODS: This trial is an open-label, non-randomized, phase II trial. Patients with platinum-pretreated metastatic neuroendocrine carcinoma were treated with 75 mg/m2/day of temozolomide for 7 days, followed by 7 days of no treatment (regimen one week on/one week off). The primary endpoint was the overall response rate. Secondary endpoints included progression-free survival (PFS), overall survival (OS), safety and tolerability. This study is registered with ClinicalTrials.gov, NCT04122911. RESULTS: From 2017 to 2020, 38 patients were enrolled. Among the patients with determined Ki67, 12 out of 36 (33.3%) had a Ki67 index <55% and the remaining 24 out of 36 (66.6%) had an index ≥55%. Overall response rate was 18% (7/38), including one complete response and six partial responses. The median PFS was 5.86 months [95% confidence interval (CI) 4.8 months-not applicable) and the median OS was 12.1 months (95% CI 5.6-20.4 months). The 1-year PFS rate was 37%. No statistically significant difference in median PFS [hazard ratio 1.3 (95% CI 0.6-2.8); P = 0.44] and median OS [hazard ratio 1.1 (95% CI 0.5-2.4); P = 0.77] was observed among patients with Ki67 <55% versus ≥55%. Only G1-G2 adverse events were registered, the most common being G1 nausea, diarrhea and abdominal pain. CONCLUSION: One week on/one week off temozolomide shows promising activity in patients with poorly differentiated NEN. The good safety profile confirmed the possibility of using this scheme in patients with poor performance status.

Impact of cinacalcet hydrochloride in clinical management of primary hyperparathyroidism in multiple endocrine neoplasia type 1.

AIM: Primary hyperparathyroidism (PHPT) is one of main cause of morbidity in patients with multiple endocrine neoplasia type 1 (MEN1). Medical therapy with cinacalcet-hydrochloride may modify the therapeutic strategy of MEN1 related PHPT. We present an experience with cinacalcet-hydrochloride in two patients with MEN1 PHPT. METHODS: The study included two MEN1 patients belonging to the same family (a 50-year-old woman and her daughter aged 20 years) with PHPT secondary to multiple involvement of parathyroid glands and other MEN1 related tumors. As both patients refused to undergo parathyroid surgery, we decided to start medical treatment with cinacalcet at the dose of 30 mg/day, which was the first treatment for the youngest patient, while the oldest had already been treated with partial parathyroidectomy. Serum concentrations of PTH, calcium and phosphorus, 24-h urine calcium-to-creatinine ratio and renal-threshold-phosphate concentration were evaluated before and after therapy. RESULTS: Serum calcium and PTH levels were normalized after 1 and 6 months of therapy, respectively, and 60 and 54 months after the beginning of cinacalcet remained normal. Hypercalciuria, hypophosphoremia and renal-threshold-phosphate normalized during therapy with cinacalcet. At ultrasonography, parathyroid nodular lesion remained unchanged. Cinacalcet was well tolerated without occurrence of side effects. CONCLUSION: Cinacalcet seems to be highly effective in controlling PHPT in patients with MEN1 either in naïve patients or in those with postsurgical recurrence. If cinacalcet will be confirmed to ensure a long-time control of PHPT or even to prevent the development and progression of PHPT, this may led to modify the therapeutic strategy of MEN1 PHPT.

A deep learning classifier for digital breast tomosynthesis.

PURPOSE: To develop a computerized detection system for the automatic classification of the presence/absence of mass lesions in digital breast tomosynthesis (DBT) annotated exams, based on a deep convolutional neural network (DCNN). MATERIALS AND METHODS: Three DCNN architectures working at image-level (DBT slice) were compared: two state-of-the-art pre-trained DCNN architectures (AlexNet and VGG19) customized through transfer learning, and one developed from scratch (DBT-DCNN). To evaluate these DCNN-based architectures we analysed their classification performance on two different datasets provided by two hospital radiology departments.DBT slice images were processed following normalization, background correction and data augmentation procedures. The accuracy, sensitivity, and area-under-the-curve (AUC) values were evaluated on both datasets, using receiver operating characteristic curves. A Grad-CAM technique was also implemented providing anindication of the lesion position in the DBT slice. RESULTS: Accuracy, sensitivity and AUC for the investigated DCNN are in-line with the best performance reported in the field. The DBT-DCNN network developed in this work showed an accuracy and a sensitivity of (90% ± 4%) and (96% ± 3%), respectively, with an AUC as good as 0.89 ± 0.04. Ak-fold cross validation test (withk = 4) showed an accuracy of 94.0% ± 0.2%, and a F1-score test provided a value as good as 0.93 ± 0.03. Grad-CAM maps show high activation in correspondence of pixels within the tumour regions. CONCLUSIONS: We developed a deep learning-based framework (DBT-DCNN) to classify DBT images from clinical exams. We investigated also apossible application of the Grad-CAM technique to identify the lesion position.

GEANT4 Monte Carlo simulations for virtual clinical trials in breast X-ray imaging: Proof of concept.

Virtual clinical trials (VCT) are in-silico reproductions of medical examinations, which adopt digital models of patients and simulated devices. They are intended to produce clinically equivalent outcome data avoiding long execution times, ethical issues related to radiation induced risks and huge costs related to real clinical trials with a patient population. In this work, we present a platform for VCT in 2D and 3D X-ray breast imaging. The VCT platform uses Monte Carlo simulations based on the Geant4 toolkit and patient breast models derived from a cohort of high resolution dedicated breast CT (BCT) volume data sets. Projection images of the breast and three-dimensional glandular dose maps are generated for a given breast model, by simulating both 2D full-field digital mammography (DM) and 3D BCT examinations. Uncompressed voxelized breast models were derived from segmented patient images. Compressed versions of the digital breast phantoms for DM were generated using a previously published digital compression algorithm. The Monte Carlo simulation framework has the capability of generating and tracking ~105 photons/s using a server equipped with 16-cores and 3.0 GHz clock speed. The VCT platform will provide a framework for scanner design optimization, comparison between different scanner designs and between different modalities or protocols on computational breast models, without the need for scanning actual patients as in conventional clinical trials.

BriXS, a new X-ray inverse Compton source for medical applications.

MariX is a research infrastructure conceived for multi-disciplinary studies, based on a cutting-edge system of combined electron accelerators at the forefront of the world-wide scenario of X-ray sources. The generation of X-rays over a large photon energy range will be enabled by two unique X-ray sources: a Free Electron Laser and an inverse Compton source, called BriXS (Bright compact X-ray Source). The X-ray beam provided by BriXS is expected to have an average energy tunable in the range 20-180 keV and intensities between 1011 and 1013 photon/s within a relative bandwidth ΔE/E=1-10%. These characteristics, together with a very small source size (~20 µm) and a good transverse coherence, will enable a wide range of applications in the bio-medical field. An additional unique feature of BriXS will be the possibility to make a quick switch of the X-ray energy between two values for dual-energy and K-edge subtraction imaging. In this paper, the expected characteristics of BriXS will be presented, with a particular focus on the features of interest to its possible medical applications.

Amebic liver abscesses: a new epidemiological trend in a non-endemic area?

BACKGROUND: Amoebic liver abscess (ALA) is the most common extraintestinal complication of colonic amebiasis. In recent decades its incidence in developed European countries has significantly increased because of travel and immigration of individuals from highly endemic areas. We report our 29-year experience in echo-guided percutaneous needle/catheter drainage (EPND/EPCD) of ALA. PATIENTS AND METHODS: From May 1979 to November 2007, 68 ALA corresponding to 56 patients were diagnosed at our Department. All patients were treated with a metronidazole plus EPND/EPCD approach. RESULTS: The majority of the cases did not need more than two echo-guided punctures. Two patients, both male immigrants (HIV-negative), had unmodified lesions after two EPNDs: catheter drainage was performed. A quick worsening of their clinical conditions and onset of neurological symptoms occurred; in both patients, computed tomography (CT) revealed a brain abscess. Intravenous medical therapy was started, but both died 4 and 3 days, respectively, after the onset of neurological symptoms (overall mortality rate: 3.57%). CONCLUSION: The unfavorable outcome of two cases is a rare example of failure of percutaneous therapy of ALA. Mortality is a possible event even in a non-endemic area such as Italy. More observational data are needed to confirm the possibility of a new epidemiological trend.

Monte Carlo calculation of monoenergetic and polyenergetic DgN coefficients for mean glandular dose estimates in mammography using a homogeneous breast model.

We computed normalized glandular dose (DgN) coefficients for mean glandular dose estimates in contemporary 2D mammography units, taking into account a homogeneous model for the breast which reflects recent literature reports. We developed a Monte Carlo code based on the simulation toolkit GEANT4 ver. 10.00. The breast was modelled as a cylinder with a semi-cylindrical section with a radius of 10 cm, enveloped in a 1.45 mm thick skin layer, as found out in recent reports in the analysis of breast computed tomography clinical scans. The compressed breast thickness was between 3 cm and 8 cm. The DgN coefficients were calculated for monoenergetic x-ray beams between 4.25 keV and 49.25 keV and were fitted with polynomial curves. Polyenergetic DgN coefficients were then computed for spectra obtained for various anode/filter combinations as adopted in routine clinical practice: Mo/Mo 30 µm (25-40 kV), Mo/Rh 25 µm (25-40 kV), Rh/Rh 25 µm (25-40 kV), W/Ag 50 µm (26-34 kV), W/Al 500 µm (26-38 kV), W/Al 700 µm (28-40 kV) and W/Rh 50 µm (24-35 kV). Monoenergetic DgN curve fit coefficients and polyenergetic DgNp coefficients were released for research and clinical work. Polyenergetic DgNp coefficients were 6% higher than those provided in the recent literature, on average. The differences range between -18% and 30%; up to 50% of the computed coefficients differed by less than 10%. The dataset of DgN coefficients are provided as tables for varying glandular fraction by mass and compressed breast thickness. Moreover, a computer code has been developed for generating user specific coefficients DgNp for user defined x-ray spectra up to 49 kV, calculated by spectral weighting from the dataset of monoenergetic DgN coefficients.

Rotational radiotherapy of breast cancer with polyenergetic kilovoltage X-ray beams: An experimental and Monte Carlo phantom study.

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.

Investigation of the refractive index decrement of 3D printing materials for manufacturing breast phantoms for phase contrast imaging.

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 ß 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/ß. 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.

Giardia and Cryptosporidium in canine faecal samples contaminating an urban area.

The aim of the present paper was to continue the study on the presence of parasitic elements in the canine faeces contaminating the urban environment of Naples (southern Italy), focussing on the protozoa Giardia and Cryptosporidium. The total number of sub-areas studied was 143, and the total number of canine faecal samples collected and examined was 415. Each faecal sample was tested for the presence of copro-antigens of Giardia and Cryptosporidium using two commercially available enzyme-linked immunosorbent assays. Giardia antigens were found in 19.6% (28/143) of the sub-areas and in 7.7% (32/415) of the canine faeces collected. Cryptosporidium antigens were found in 4.2% (6/143) of the sub-areas and in 1.7% (7/415) of the canine faeces collected. Co-infection was not found in any sample. The results of the logistic regression models did not show any association between the positivity to Giardia or Cryptosporidium and the independent demographic variables (human population density, male and female population density) taken into consideration. In conclusion, the findings of the present study revealed the presence of Giardia and Cryptosporidium in canine faecal samples from the urban environment of Naples; however, the zoonotic potential of these findings was not assessed due to the lack of information on species/genotypes detected.

Homogeneous vs. patient specific breast models for Monte Carlo evaluation of mean glandular dose in mammography.

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.

Normalized glandular dose coefficients in mammography, digital breast tomosynthesis and dedicated breast CT.

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.

Evaluation of the BreastSimulator software platform for breast tomography.

The aim of this work was 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 tomography (CT) scanners dedicated to the breast. Eight 3D digital breast phantoms were created with glandular fractions in the range 10%-35%. 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 CT images acquired from two different clinical breast CT scanners were used for comparison purposes. The quantitative evaluation included calculation of the power-law exponent, ß, from simulated and real breast tomograms, based on the power spectrum fitted with a function of the spatial frequency, f, of the form S(f) = α/f ß . The breast models were validated by comparison against clinical breast CT and published data. We found that the calculated ß coefficients were close to that of clinical CT data from a dedicated breast CT scanner and reported data in the literature. In evaluating the software package BreastSimulator to generate breast models suitable for use with breast CT imaging, we found that the breast phantoms produced with the software tool can reproduce the anatomical structure of real breasts, as evaluated by calculating the ß exponent from the power spectral analysis of simulated images. As such, this research tool might contribute considerably to the further development, testing and optimisation of breast CT imaging techniques.

Energy dependent calibration of XR-QA2 radiochromic film with monochromatic and polychromatic x-ray beams.

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.

Glandular dose in breast computed tomography with synchrotron radiation.

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.