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Background: Survival data support the use of first-line osimertinib as the standard of care for epidermal growth factor receptor (EGFR)-positive non-small cell lung cancer (NSCLC). However, it remains unclear whether upfront osimertinib is superior to sequential first-or second-generation tyrosine kinase inhibitors (TKIs) followed by osimertinib for all patients. It is impossible to predict which patients are at high risk of progression, and this constitutes a major limitation of the sequential TKI approach. Patients and methods: A total of 830 plasma samples from 228 patients with stage IV, EGFR-positive NSCLC who were treated with first-line TKIs were analysed by digital polymerase chain reaction (dPCR). Results: The circulating tumour DNA (ctDNA) levels helped to identify patients with significantly improved survival rate, regardless of the treatment. Patients treated with first-or second-generation TKIs (N = 189) with EGFR mutations in plasma at a mutant allele frequency (MAF)

This work presents a technique to perform an electronic portal imaging device (EPID) signal planar calibration into dose terms using Monte Carlo simulations. To that, a complete Monte Carlo (MC) simulation of a radiotherapy treatment linear accelerator including a multi-leaf collimator system (MLC) and an EPID has been developed. Several solid water blocks were used to obtain calibration measurements and simulations with a large dose range in order to study the relation between the squared EPID response and the MC calculated dose. The calibrated EPID has also been used as a dosimetric tool to validate the MC MLC Linac model. Simulation and measurement comparisons are below 5% root mean square of percentage dose difference. This technique could potentially provide a more accurate verification of dose delivery to heterogeneous anatomical regions in patients receiving complex multi-field conformal radiation therapy treatments.

An accurate knowledge of the photon spectra emitted by X-ray tubes in radiodiagnostic is essential to better estimate the imparted dose to patients and to improve the quality image obtained with these devices. However, it is difficult to measure the energy spectrum of these tubes due to the pile up effect produced by the high fluence of X-ray beams. In this work, it is proposed the use of a flat panel detector together with a PMMA wedge to obtain a dose distribution for different high voltages. The relation between the dose curve recorded by the flat panel and the primary beam X-ray spectrum is defined by a Response matrix. The MCNP5 code based on the Monte Carlo method has been used to simulate the actual experimental acquisition including the X-ray tube, the PMMA wedge and a flat panel. A Response matrix has been obtained by means of different monochromatic beams. Knowing the dose distribution for a given conditions and the Response matrix, the primary spectrum can be obtained. The Modified Truncated Singular Value Decomposition (MTSVD) method has been applied to unfold primary spectra using Matlab © algorithms. Unfolded spectra are compared with theoretical X-ray spectra obtained from IPEM 78 catalogue report. Results show that the hybrid technique -experimental-Monte Carlo method- could represent a valid tool in order to complement the Quality Control of X-ray tubes in the radiodiagnostic energy range.

[EN] The assessment and control of image quality is a fundamental task associated with good practice to guarantee a suitable diagnosis by the radiologist. The need for image quality assessments in radiography is well established, and the use of test phantoms is a common method for this purpose. In this work we present a developed tool that consists of a specific phantom (named RACON) that is used for acceptance and constancy test in order to analyze the image obtained by digital radiographic equipment, software (named SoftRACON) for automated image analysis with digital processing techniques, and a database to store test phantom images and the scoring results. The main objective is to characterize the constancy of the radiographic imaging chain and guarantee acceptable image quality, related to well-functioning of the radiographic equipment. Therefore, the application presented in this work is sensitive enough to the operating conditions of the radiographic digital equipment and allows the assessment of the imaging system quality and, consequently, increases the objectivity (accuracy) in the evaluation of the image.

Induced radioactivity and photoneutron contamination inside a radiation therapy bunker of a medical linear accelerator (Linac) is investigated in this work. The Linac studied is an Elekta Precise electron accelerator which maximum treatment photon energy is 15 MeV. This energy exceeds the photonuclear reaction threshold (around 7 MeV for high atomic number metals). The Monte Carlo code MCNP6 has been used for quantifying the neutron contamination inside the treatment room for different gantry rotation configuration. Walls activation processes have also been simulated. The approach described in this paper is useful to prevent the overexposure of patients and medical staff.

A Theratron 780 (MDS Nordion) "Co radiotherapy unit has been simulated with the Monte Carlo code MCNP. The unit has been realistically modelled: the cylindrical source capsule and its housing, the rectangular collimator system, both the primary and secondary jaws and the air gaps between the components. Different collimator openings, ranging from 5 x 5 cm 2 to 20 x 20 cm 2 (narrow and broad beams) at a source-surface distance equal to 80 cm have been used during the study. In the present work, we have calculated spectra as a function of field size. A study of the variation of the electron contamination of the 6 0 Co beam has also been performed.

Mammographic phantom images are usually used to study the quality of images obtained by dedicated mammographic equipment. The digital image treatment techniques allow us to carry out an automatic analysis of the phantom image. In this work, some techniques of digital image processing are applied to compute a specific image quality index (IQI) for a mammographic phantom, namely CIRS model 11A version SP01. The algorithm designed analyses the phantom image by means of automatic detection of the number of microcalcifications, and the image resolution as the number of line pairs per millimetre. Then, the IQI is calculated from a scoring system. The manner in which the functioning conditions (kV and mAs) of the mammographic equipment and the preprocessing denoising method of the digital image affect the results for the IQI are also studied.

Monte Carlo estimation of the giant-dipole-resonance (GRN) photoneutrons inside the Elekta Precise LINAC head (emitting a 15 MV photon beam) were performed using the MCNP6 (general-purpose Monte Carlo N-Particle code, version 6). Each component of LINAC head geometry and materials were modelled in detail using the given manufacturer information. Primary photons generate photoneutrons and its transport across the treatment head was simulated, including the (n, γ) reactions which undergo activation products. The MCNP6 was used to develop a method for quantifying the activation of accelerator components. The approach described in this paper is useful in quantifying the origin and the amount of nuclear activation.

The image quality assessment in radiographic equipments is a very important item for a complete quality control of the radiographic image chain. The periodic evaluation of the radiographic image quality must guarantee the constancy of this quality to carry out a suitable diagnosis. Mammographic phantom images are usually used to study the quality of images obtained by determined mammographic equipment. The digital image treatment techniques allow to carry out an automatic analysis of the phantom image. In this work we apply some techniques of digital image processing to analyze in an automatic way the image quality of mammographic phantoms, namely CIRS SP01 and RACON for different varying conditions of the mammographic equipment. The CIRS SP01 phantom is usually used in analogic mammographic equipments and the RACON phantom has been specifically developed by authors to be applied to acceptance and constancy tests of the image quality in digital radiographic equipments following recommendations of international associations. The purpose of this work consists in analyzing the image quality for both phantoms by means of an automatic software utility. This analysis allows us to study the functioning of the image chain of the mammographic system in an objective way, so an abnormal functioning of the radiographic equipment might be detected.

A precise estimation of the photon spectra emitted by radiation therapy Linacs is especially important to accurately estimate the dose received by patients in order to improve treatment plannings. Moreover the knowledge of the spectra is useful to perform routinely Quality Control procedures of these equipments. In this work we propose the use of the Elekta Linac EPID (Electronic Portal Imaging Device) to obtain the fluence spectrum emitted by this unit. To that, several images using different thicknesses of solid water slabs have been taken with the EPID, setting 100 UM, a 10 cm×10 cm field size and a 6 MeV energy beam. The relation between the signal response recorded by the EPID with several solid water slabs and the primary photon spectrum emitted is calculated by means of a Response matrix, which has been performed via Monte Carlo simulations. To that, the MCNP5 code has been used to simulate the EPID signal response obtained after irradiation with consecutive monoenergetic beams for different slabs. Each row of the Response Matrix represents the Monte Carlo EPID signal registered using a specific energy bin. Since this matrix is ill conditioned we have applied the Truncated Singular Value Decomposition algorithms to unfold the spectra. Results have been compared with theoretical spectrum, showing that the mixed methodology (experimental-Monte Carlo simulation) can offer an accurate way to determinate the photon spectrum in radiation therapy.

Numerous improved physics-based methods for Linac photon spectra reconstruction have been published; some of them are based on transmission data analysis and others on scattering data. In this work, the two spectrum unfolding approaches are compared in order to experimentally validate its robustness and to determine which is the optimal methodology for application on a clinical quality assurance routine. Both studied methods are based on EPID images generated when the incident photon beam impinges onto plastic blocks. The distribution of transmitted/scatter radiation produced by this object centered at the beam field size was measured. Measurements were performed using a 6 MeV photon beam produced by the linear accelerator. The same radiation distribution conditions were also simulated with Monte Carlo code for a series of monoenergetic identical geometry photon beams for both cases. Two systems of linear equations were generated to combine the polyenergetic EPID measurements with the monoenergetic simulation results. Regularization techniques were applied to solve the systems for obtaining the incident photon spectrum. We present a comparison between the well-known photon Spectral Reconstruction based on Transmission Data (Trans-based) technology and the Spectral Reconstruction based on Scattering Data (Scatt-based), which we both developed using EPID images. It is shown that Trans-based reconstruction results display much better agreement with photon spectrum theoretical predictions.

External Bremsstrahlung photon beams produced by medical linac accelerators (Linac) are the most commonly used radiation therapy treatments. The case of treatments which include photon energy beam exceeding 10 MeV produce an undesired dose received by patients due to photoneutron production in the accelerator head. Currently, sophisticated techniques such as multileaf collimators are used for a better definition of the target volume irradiation. In these cases it is important to evaluate the photoneutron dose produced by the excitation of the high atomic number materials (mainly tungsten) constituting the collimator leaves in order to optimize the radiation therapy treatment. A Monte Carlo simulation has been developped to calculate the photoneutron dose arising from an Elekta Precise unit head using a 15 MeV photon beam. The simulation has been performed using the MCNP5 code. Results are presented for the facility at Hospital Universitari Clinic de Valencia setting a square 10 cm × 10 cm collimator configuration.

Megavoltage photon beams are widely used for radiation therapy treatments, and the precise knowledge of their spectral distribution is important for accurate dose calculations. There are several methods that can offer reasonable estimations of linac photon spectra based on measured depth dose distributions in a water tank. However, this reconstruction problem is an inverse radiation transport function which is poorly conditioned and its solution may become unstable due to small perturbations in the input data. We present here a novel and more stable method which can be used for photon spectral reconstruction without any prior knowledge of spectral distribution. This technique involves measuring the depth dose curve in a water phantom and applying an unfolding method using Monte Carlo simulated depth dose gradient curves for consecutives mono-energetic beams. It is shown that the relative errors in dose calculations, using the spectra reconstructed via this method, are significantly smaller than those obtained via the traditional reconstruction algorithms. These results suggest that this gradient algorithm could be useful in linac photon spectra routines calibration.

[EN] An accurate knowledge of the spectral distribution emission is essential for precise dose calculations in radiotherapy treatment planning. Reconstruction of photon spectra emitted by medical accelerators from measured depth dose distributions in a water cube is an important tool for commissioning a Monte Carlo treatment planning system. However, the reconstruction problem is an inverse radiation transport function which is poorly conditioned and its solution may become unstable due to small perturbations in the input data. In this paper we present a more stable spectral reconstruction method which can be used to provide an independent confirmation of source models for a given machine without any prior knowledge of the spectral distribution. This technique involves measuring the depth dose curve in a water phantom and applying an unfolding method using Monte Carlo simulated depth dose gradient curves for consecutives mono-energetic beams. We illustrate this theory to calculate a 6 and a 15 MeV photon beam emitted from an Elekta Precise radiotherapy unit using the gradient of depth dose curves in a cube-shaped water tank.

[EN] Megavoltage sources are commonly used in radiotherapy treatments, and the determination of the spectral distribution of a photon beam is extremely important for exact dosimetry and for the calculation of therapeutic dose distributions. Since direct measurements of the spectrum are very difficult, we present a technique to accurately calculate the bremsstrahlung spectra based on a numerical reconstruction upon central-axis depth dose data measured in a water tank using inverse methods. The basic idea of this technique is that the measured depth dose curve can be expressed as a weighted superposition of monoenergetic depth dose curves. While traditional approaches directly use the measured depth dose data, we show the improvement of using the gradient of these data for reconstruction. The inverse problem in terms of gradients is shown to be markedly less illconditioned than the usual inverse problem. In each case, a Tikhonov regularization is introduced to minimize the effects of noise due to measurement and computation. We illustrate this theory to calculate a 6-MeV photon beam from an Elekta Precise radiotherapy unit utilizing the gradient of depth dose measurements in a water tank.

Megavoltage photon sources are normally used for radiotherapy treatments. For these equipments an accurate knowledge of their spectral distribution is essential for accurate dose calculations planning. There are several ways to determine the spectrum of a clinical photon beam: direct measurement, electron source modelling or reconstruction from experimental measures. In this paper we focus on the latter type of spectral reconstruction methods which can be used to provide an independent confirmation of source models for a given machine without any prior knowledge of the spectral distribution. This technique involves measuring the depth dose curve in a water phantom and applying an unfolding method using Monte Carlo simulated depth dose curves for consecutives mono-energetic beams. We illustrate this theory to calculate a 6 MeV photon beam from an Elekta Precise radiotherapy unit using the gradient of depth dose measurements in a cube-shaped water tank.

Commercial planning systems used in radiotherapy treatments use determinist correlations to evaluate dose distribution around regions of interest. Estimated dose with this type of planners can be problematic, especially when analyzing heterogeneous zones. The present work is focused in quantifying the dose distribution in a heterogeneous medium irradiated by a 6 MeV photon beam emitted by an Elekta Precise Radiotherapy Unit head. Dose mapping inside the heterogeneous water phantom has been simulated with the photon and electron transport with Monte Carlo computer code MCNP5 and also, using a commercial treatment planning software in the same irradiation conditions. The calculated results were compared with experimental relative dose curves. This comparison shows that inside the heterogeneity region, the commercial algorithms are not able to predict the variation of dose in the heterogeneous zones with the same precision as MCNP5.

This work is mainly focused on developing a methodology to obtain portal dosimetry with an amorphous silicon electronic portal image device (EPID) by means of Monte Carlo simulations and experimental measures. According to this, pixel intensity values of portal images have been compared with dose measured from an ionization chamber and dose obtained from Monte Carlo simulations. To that, several images were acquired with the Elekta iView GT EPID using an attenuator phantom slab (10 cm thickness of solid water) and a 6 MV photon energy beam with different monitor units. The average pixel value in a region of interest (ROI) centered at the beam selecting each image was extracted and compared to dose measures performed with the ionization chamber. These parameters were found to be linearly correlated with the number of monitor units (MU). Since, MCNP5 simulations allow calculating the deposited dose in the ROI within the phosphor layer of the EPID model, we can compare the portal dose with the simulated transit dose in order to perform a treatment control.

Mammographic phantom images are usually used to study the quality of images obtained by determined mammographic equipment. The digital image treatment techniques allow carrying out an automatic analysis of the phantom image. Nowadays, the digital radiographic equipments are replacing the traditional film-screen equipments and it is necessary to update the parameters to guarantee the quality of the process. In this work we apply some techniques of digital image processing to compute a specific image quality indexes for mammographic phantoms, namely CIRS SP01 and CDMAM 3.4. to study the evolution of this parameter with different varying conditions of the mammographic equipment. The indexes are calculated from a scoring system based on a designed algorithm which analyses the phantom image by means of an automatic detection of the test objects in each phantom.

In Mammographic phantom images are usually used to study the quality of images obtained by determined mammographic equipment. The digital image treatment techniques allow carrying out an automatic analysis of the phantom image. Nowadays, the digital radiographic equipments are replacing the traditional film-screen equipments and it is necessary to update the parameters to guarantee the quality of the process. In this work we apply some techniques of digital image processing to compute a specific image quality indexes for mammographic phantoms, namely CIRS SP01 and CDMAM 3.4. to study the evolution of this parameter with different varying conditions of the mammographic equipment. The indexes are calculated from a scoring system based on a designed algorithm which analyses the phantom image by means of an automatic detection of the test objects in each phantom.

In this work we have designed some specific phantoms to study the obtained image of computerized and direct digital radiographic equipments to characterize the constancy of the imaging chain. The developed phantoms are applied for different radiographic digital devices, as conventional equipments with computed radiography (phosphor plate) and direct radiography (sensor) technology. These phantoms have specific characteristics for these systems, as different test zones for the analysis of the image quality. The test zones that are in these phantoms are low contrast objects, varying in diameter and size, for the threshold contrast resolution of the system, high resolution test for the limiting spatial resolution, dynamic step wedge for the dynamic range of grays of the system, homogeneity zone and alignment marks for position and size of radiation field. Additionally, we have developed a software based on automatical processing techniques to analyze the image obtained by the radiographic equipment with digital processing techniques as edge detector, morphological operators, statistical test for the detected combinations. The images have been acquired in DICOM format and they can be analyzed with objective parameters as an image quality index and the contrast detail curve. The design of these phantoms let the evaluation of a wide range of operating conditions of voltage, current and time of the digital radiographic equipments and the functioning of the image chain of the digital system applied to its quality control for image quality and radiation exposure.

Radioactive liquid wastes of low-medium activity level are generated in radio immune assay (RIA) laboratories, which are also potentially infectious because of the pathogens from patient blood. The most common way of managing these wastes consists of a temporal storage, for partial radioactivity decay, followed by management by an authorised company. The object of this work is to study the viability of treating radioactive liquid wastes coming from RIA using membrane techniques in order to reduce their volume, which would mean an improvement from the radiological point of view and a decrease in management costs. This paper describes the results of some experiments carried out with RIA real wastes, by means of processes such as ultrafiltration and reverse osmosis. It has been proved that waste volume can be significantly reduced, obtaining a treated liquid that is free of pathogens and organic matter and with an activity level around the environmental background.

The aim of this study is the development of a methodology to reconstruct via Monte Carlo techniques the radiographic image of the CIRS 11 A (MAMMO PHANTOM SP01) phantom. This phantom is used in image quality assessment during quality control tests in breast screening locations and other health centers. The mammographic phantom is comprised of a reference point, a glandular tissue step wedge, contrast and resolution targets, and groups of microcalcifications and fibers. The MCNP radiation transport code (version 4c2) has been modified and recompiled to let use of a large number of tallies and detectors per input file, and an azimuthal directional source biasing. The output surface air kerma (OSAK) delivered by the X-rays has been scored employing a rectangular matrix of point detectors (F5 tally) under the phantom, simulating the image system. Some variance reduction techniques have been implemented to ensure that photons reach the detectors and that weight fluctuations were reduced. The characteristic curve of the film-scanner imaging system combination has been obtained throughout several experimental measures with an aluminium sensitometric wedge and Monte Carlo simulations. The reconstructed images agree with the range of values, indicating that this method would be suitable for training purposes, phantom designing or dose calculations.

Mammographic phantoms are employed during quality control test in breast screening locations and other health centres. These quality controls are performed to achieve the image quality required to detect breast abnormalities, ensuring the minimum risk to radiographied women. The aim of this study is the development of a methodology to reproduce the image of a mammogram during a routine exposure in a breast screening programme. In a first step, the CIRS 11A (MAMMO PHANTOM SP01) mammographic phantom has been simplified and modelled with the Monte Carlo transport code MCNP-4c2. Different tallies (F2 and F5) have been used to score the photon flux under the phantom, and a group of aluminium layers (99.9% purity) have been employed to reconstruct the characteristic curve, which transforms output air kerma in a grey-scale level. The code has been modified to produce photons in a semi-cone, allowing any polar and azimuthal angle. Furthermore, different tally bins have been introduced to count photons in each pixel of the final image, improving computer time simulations. The horizontal resolution target has been reproduced at different tube loadings and pixel pitches. The reconstructed images agree with the range of values, indicating that this method would be suitable for training purposes, phantom designing or dose calculations

A method has been developed to analyse the digital image quality of mammographic images by means of automatic process techniques. The techniques used for the digital image treatment are standard techniques as the image thresholding to detect objects, the regional growing for pixels pooling and the morphological operator application to determine the objects shape and size, etc. This study allows the obtention of information about the microcalcifications, that due to its small size and lowly contrast can be obtained very difficultly by direct observation. The final aim of this work is to obtain one or more parameters to characterize the quality image in an objective way. These parameters will serve to compare images obtained at different mammographic centers and also, to study the temporal evolution of the image quality produced by determined mammographic equipment.

Poster: "ECR 2013 / C-1596 / Preliminary results of early assessment of response with perfusion-CT in patient with metastatic renal cell carcinoma treated with sunitinib" by: "A. D. Sotomayor1, B. Pano Brufau2, J. M. Gutierrez1, B. Mellado2, O. Reig2, M. C. Sebastia2; 1Barcelona, Barcelona/ES, 2Barcelona/ES"

Aim: The IR has been associated with increased risk of breast cancer (BC) and as a poor prognostic factor for relapse and survival. There is a lack of prospective studies that have reviewed the impact of IR across the NAC time and the likelihood of pCR. We determined the association between IR by HOMA2 (homeostasis model assessment) and pCR in LIBC. Methods: It was a prospective cohort, multicenter study. From 2012 to 2013, 64 patients were enrolled. Metabolic syndrome (MS) diagnosis was made by ATP III criteria. Insulin and glucose were measured at baseline and every 3 weeks during NAC. The IR was calculated by HOMA2 –IR.® Cut off value to define IR: HOMA2 ≥1.9. pCR (breast + nodes) was defined as no residual IBC. Results: Median age was 49 years. Axillary nodes were involved in 37 (57.8%). cTNM stage was II 50 (78.1%) and III 14 (21.8%). pCR (full cohort) was 37.5%. pCR in luminal A/B-like, triple negative and HER2 was 15.6%, 61.1% and 57.1% respectively. 25% had MS at baseline and up to 40% (final evaluation). At baseline 29 (45.3%) had IR and in final 34 (53.1%) (p = 0.005). We observed a gradual and almost linear increase of IR during the NAC time (p = 0.019). The group without IR (baseline) had a higher likelihood of pCR (HR 3.1, 95% CI 1.3-7.3). In the pCR group the HOMA2 remained below or slightly above 1.9 and with no changes over time (p = 0.225). Inversely in the no pCR group the IR increased over time and almost with a linear trend (p = 0.013). In a repeated measures analysis of HOMA2 over NAC time in the three biological subgroups, differences were observed only in luminal-like (p = 0.044). Comparing quartiles (Q1-2 vs Q3-4), basal insulin (p =0.018) and basal HOMA2 (p = 0.032) were significantly associated with pCR. In an adjusted logistic regression analysis for pCR, the IR remained as an independent factor for pCR (p = 0.018). Conclusions: We found a strong association between the status of IR and the likelihood of pCR in neoadjuvant setting of BC. To our knowledge this is the first prospective study describing the natural history of IR across time of the NAC. The IR increased over time of the NAC and the pCR likelihood is inversely associated with IR. Our findings suggest that the increase in central adiposity during NAC time produces a greater insulin resistance and thereby a cell proliferative environment resulting in a lower response to NAC. Disclosure: All authors have declared no conflicts of interest.

Background The BMI is a clinical parameter that although not perfect is often used to measure adiposity. In breast cancer there are multiple studies indicating that overweight/obesity (O/O) is related with lower survival and increased risk of relapse. It has been also reported less likely to achieve a pathological complete response (pCR) after neoadjuvant chemotherapy (NAC) in O/O patients. Methods We retrospectively reviewed the records of 108 patients diagnosed with invasive locally advanced breast cancer (ILABC) who had been treated with NAC (anthracycline + taxane ± trastuzumab). The aim of our study was to review the impact of BMI on the pCR and the possibility of recurrence. pCR was defined as the criterion of strict pCR breast+nodes. Results From 2004 to 2011, 108 patients received NAC. Based on their weight and height at baseline we divided into two groups; group 1: underweight/normal (BMI Conclusions Despite the retrospective nature of this study we can conclude that the patients with ILABC and O/O have a high risk for relapse and decreased response to NAC. It requires well-designed prospective studies to control confounding factors (dose intensity, chemotherapy regimens, changes in BMI) to get clear answers of these associations. Disclosure All authors have declared no conflicts of interest.

This work is focused on developing a methodology to obtain portal dosimetry with an amorphous silicon Electronic Portal Image Device (a-Si EPID) used in radiotherapy by means of Monte Carlo simulations and experimental measures. Pixel intensity values from portal images have been compared with dose measured from an ionization chamber and dose calculated from Monte Carlo simulations. To this end, several images were acquired with the Elekta iView GT EPID using an attenuator phantom slab (10 cm thickness of solid water) and a 6 MeV photon energy beam with different monitor units settings (MU). The average pixel value in a region of interest (ROI) centered at the beam for each image was extracted and compared to dose measures performed with an ionization chamber. These parameters were found to be linearly related with the number of monitor units. Since MCNP5 simulations allow calculating the deposited dose in the ROI within the phosphor layer of the EPID model, we could compare the portal dose with the simulated transit dose in order to perform a treatment control.

The development of specific phantoms to study the image obtained by computerized and direct digital radiographic equipment is the objective of this work to characterize the physical properties of the image chain. We have developed a specific phantom, named RACON, that is applied to an acceptance and constancy test to assess the image quality of digital radiographic equipment. This phantom has been designed with different test objects recommended by international and national associations (IEC-61223-2-9, RD 1976―1999) as low-contrast objects varying in diameter and size for threshold contrast resolution, a high-resolution test for the limiting spatial resolution, a dynamic step wedge for the dynamic range of the system, and a homogeneity zone and alignment marks for the position and size of the radiation field. Furthermore, we have developed specific software to analyze automatically and objectively the phantom images. The algorithms are based on digital image processing techniques, and they have been specifically designed for each test object in the phantom. The developed phantom is sensitive enough to the operating conditions of the radiographic digital system, and the automatic image evaluation allows the objective study of the global state of the image system.

The work focuses on reconstructing, by means of a scatter analysis method, the primary beam photon spectrum of a linear accelerator. This technique is based on irradiating the isocenter of a rectangular block made of methacrylate placed at 100 cm from the source and measuring scattered particles around the plastic at several specific positions with different scatter angles. The MCNP5 Monte Carlo code has been used to simulate the particle transport of monoenergetic beams and register the scatter measurement after contact with the attenuator. Measured ionization values are input necessary for calculating the spectrum as the sum of monoenergetic individual energy bins using the Schiff bremsstrahlung model. The measurements have been made in an Elekta Precise linac using a 6-MeV photon beam. Relative depth and profile dose curves calculated in a water phantom using the reconstructed spectrum agree with the experimentally measured dose data to within 5%.

The purpose of this work is to assess the image quality of dental digital systems with computed radiography (phosphor plate) and direct radiography (charge-coupled-device sensor), by developing a s...

Nowadays, the digital radiographic equipments are replacing the traditional film-screen equipments and it is necessary to update the parameters to guarantee the quality of the process. Contrast-detail phantoms are applied to digital radiography to study the threshold contrast-detail sensitivity at operation conditions of the equipment. The phantom that is studied in this work is CDMAM 3.4. One of the most extended indexes to measure the image quality in an objective way is the image quality figure (IQF). The aim of this work is to study the image quality of different images contrast-detail phantom CDMAM 3.4, carrying out the automatic detection of the contrast-detail combination and to establish a parameter which characterize in an objective way the mammographic image quality. This is useful to compare images obtained at different digital mammographic equipments to study the functioning of the equipments that facilitates the evaluation of image contrast and detail resolution.

The present work is centered in reconstructing by means of a scatter analysis method the primary beam photon spectrum of a linear accelerator. This technique is based on irradiating the isocenter of a rectangular block made of methacrylate placed at 100 cm distance from surface and measuring scattered particles around the plastic at several specific positions with different scatter angles. The MCNP5 Monte Carlo code has been used to simulate the particles transport of mono-energetic beams to register the scatter measurement after contact the attenuator. Measured ionization values allow calculating the spectrum as the sum of mono-energetic individual energy bins using the Schiff Bremsstrahlung model. The measurements have been made in an Elekta Precise linac using a 6 MeV photon beam. Relative depth and profile dose curves calculated in a water phantom using the reconstructed spectrum agree with experimentally measured dose data to within 3%.