Screening of MRSA colonization in patients undergoing total joint arthroplasty.

BACKGROUND: Periprosthetic infection is commonly caused by Staphylococcus aureus and, if resistant to methicillin (MRSA), is associated with increase in severity and costs to patient and healthcare systems. MRSA colonizes 1-5% of the population, therefore using a screening and decolonisation protocol the risk of periprosthetic infection could be reduced. The objective of our study is to report the results of a preoperative MRSA screening and management protocol utilised at our hospital. METHODS: All patients undergoing a total joint arthroplasty at our hospital were preoperatively screened for MRSA colonization with swab samples of five different locations. Exposure to risk factors were investigated in colonised patients and they were treated for 5 days prior surgery with nasal mupirocin, chlorhexidine sponges and oral tablets. RESULTS: During the 48 months of the study, MRSA colonisation was identified in 22 (1.01%) of 2188 patients operated. The culture was positive only in the nasal swab in 55 patients. In five patients the nasal culture was negative, but they had another positive swab culture (three in the groin and two perianal). None of the patients reported a history of recent antibiotic treatment or hospitalization. CONCLUSION: At our institution, the prevalence of MRSA colonisation is 1.01% in patients undergoing hip and knee arthroplasty. Interestingly, our screening protocol included samples from five different anatomic locations, and it is important to highlight that we found patients with negative nares culture and positive cultures in other locations. Therefore, the number of carriers may be underdiagnosed if only nasal samples are obtained. LEVEL OF EVIDENCE: IV.

Study of the photoneutron generation caused by a LinAc Beryllium window with a 6 MeV treatment beam.

In most conventional radiation therapy treatments, special attention is payed for neutron contamination when working with energy beams above 8 MeV and generally it is only considered for shielding requirements, not for dose study in patients or employees. The present work is focused on studying the unwanted generated photoneutrons in a Medical Linear Accelerator (LinAc) Varian TrueBeam using a 6 MeV radiation treatment beam. To that, Monte Carlo (MC) simulation code MCNP6.1.1 was used. This version of the code allows the use of unstructured mesh geometries as a novelty, offering more reliable results and higher speed computation. The particularity of the studied LinAc is the presence of a beryllium filter at the treatment head. Since Beryllium causes photonuclear reactions (γ, n) at energies much lower than other LinAc composing materials, this work aims to analyze if this type of units, when using low energy treatment beams (6 MeV), produce neutron pollution and to ensure that this unwanted radiation can be considered negligible.

Brachytherapy organ dose estimation using Monte Carlo simulations of realistic patient models.

Radiation Therapy Planning Systems (RTPS) currently used in hospitals contain algorithms based on deterministic simplifications that do not properly consider electrons lateral transport in the areas where there are changes of density, and as a result, erroneous dose predictions could be produced. According to this, the present work proposes the use of Monte Carlo method in brachytherapy planning systems, which could affect positively on the radiotherapy treatment planning, since it provides results that are more accurate and takes into account the in homogeneities density variations. This paper presents a Monte Carlo (MC) simulation of a brachytherapy prostate treatment with I-125 seeds, using the latest version of MCNP, v.6.1.1. To that, a 3D model of the anatomy of a real anonymized patient is created from the segmentation of Computed Tomography (CT) images. Treatment over this 3D model is simulated and the dose given to each organ is obtained. These doses are compared with those calculated by deterministic planning system used in hospital demonstrating the effectiveness of MC method in the planning of brachytherapy treatments, because of not only the results precision but also regarding the affordable computing times.

Dose calculation in computerized tomography.

The purpose of this work is to develop an automatic methodology to obtain the dose received by a patient, (classified by organs), after being subjected to ionizing radiation because of CT images acquisition. The methodology starts from CT images, these images are automatically segmented and voxelized taking into account the CT numbers in order to obtain a 3D model used in Monte Carlo Simulations to calculate the dose inside the patient.Monte Carlo codes used in this work are MCNP.6.1.1, (whose results will be taken as a reference values) and MC-GPU, which appears to be a good candidate to be implemented in the methodology since his GPU parallelization offers a high speed calculation. Results show good agreement between simulated values obtained by MC-GPU and MCNP6.1.1.

A compendium of developmental gene expression in Lake Malawi cichlid fishes.

BACKGROUND: Lake Malawi cichlids represent one of a growing number of vertebrate models used to uncover the genetic and developmental basis of trait diversity. Rapid evolutionary radiation has resulted in species that share similar genomes but differ markedly in phenotypes including brains and behavior, nuptial coloration and the craniofacial skeleton. Research has begun to identify the genes, as well as the molecular and developmental pathways that underlie trait divergence. RESULTS: We assemble a compendium of gene expression for Lake Malawi cichlids, across pharyngula (the phylotypic stage) and larval stages of development, encompassing hundreds of gene transcripts. We chart patterns of expression in Bone morphogenetic protein (BMP), Fibroblast growth factor (FGF), Hedgehog (Hh), Notch and Wingless (Wnt) signaling pathways, as well as genes involved in neurogenesis, calcium and endocrine signaling, stem cell biology, and numerous homeobox (Hox) factors-in three planes using whole-mount in situ hybridization. Because of low sequence divergence across the Malawi cichlid assemblage, the probes we employ are broadly applicable in hundreds of species. We tabulate gene expression across general tissue domains, and highlight examples of unexpected expression patterns. CONCLUSIONS: On the heels of recently published genomes, this compendium of developmental gene expression in Lake Malawi cichlids provides a valuable resource for those interested in the relationship between evolution and development.

Efectividad y eficiencia de la vía clínica rápida (fast-track) en prótesis total de rodilla y cadera (PTR y PTC): 11 años de experiencia. Validación de la vía clínica. Análisis de la estancia hospitalaria, tasa de revisiones y coste en un hospital público español / Effectiveness and efficiency of the fast-track protocol in total hip and knee arthroplasty (THA and TKA): 11 years of experience. validation of the protocol, analysis of hospital stay, rate of revision surgery and cost in a Spanish public hospital

Objetivo. a) Valorar la efectividad de la implementación del fast-track en PTR-PTC; y b) evaluar la eficiencia en la estancia hospitalaria, las cirugías de revisión y los costes. Material y métodos. Estudio observacional en 2 tiempos: 1) Estudio prospectivo con 200 pacientes (PTR=100, PTC=100) en 2005-2007. Se analizó la edad, el sexo, la estancia hospitalaria, la escala visual analógica (EVA), el balance articular (BA) de rodilla, las complicaciones y la rehabilitación tras el alta. 2) Estudio prospectivo a 3.094 PTR y 1.664 PTC, desde el 2005-2015. Se analizó la estancia hospitalaria, el porcentaje de cirugías de revisión y el ahorro estimado. Resultados. En la validación en PTR el 68% (n=68) eran mujeres y el 32% (n=32) varones. La edad media fue de 71 años y la estancia hospitalaria de 6 días. La EVA preoperatoria/6 meses/año/2 años disminuyó progresivamente (7; 1,8; 1,4 y 1,2). El BA al alta/mes/2 años mejoró progresivamente (82°, 90° y 93°). Complicaciones 3% (n=3; fractura postraumática y 2 inestabilidades). Rehabilitación ambulatoria 8% (n=8). En la validación en PTC el 48% (n=48) eran mujeres y el 52% (n=52) varones, con una edad media de 70 años. La estancia hospitalaria fue de 5 días. Hubo complicaciones en 3 pacientes (3%) (fractura, luxación y TVP). Rehabilitación ambulatoria 3% (n=3). En PTR la estancia media (11 años) fue 5,96 días, las revisiones 5,96% y el ahorro estimado (2013-2015) 117.776 euros. En PTC la estancia media (11 años) fue 6,24 días, las revisiones 10,62% y el ahorro estimado (2013-2015) 116.316 euros. Conclusiones. La implantación/seguimiento del protocolo fast-track en PTR-PTC disminuye el dolor, las complicaciones, la rehabilitación ambulatoria, la estancia hospitalaria, la tasa de revisiones y los costes (AU)

Objective. a) To validate the effectiveness of the implementation of a fast-track protocol for TKA-THA; b) to evaluate efficiency in reducing length of stay, hospital costs and revision surgeries. Material and methods. A two-phase observational study was performed: 1) A prospective study in 200 patients (100 TKA and 100 THA) between 2005 and 2007. Age, sex, length of stay, visual analog scale (VAS) for pain, knee range of movement (ROM), complications and post-discharge rehabilitation were analyzed. 2) A prospective study was conducted in 3094 TKA and 1664 THA patients between 2005 and 2011. Length of stay, revision surgery and estimated savings were analyzed. Results. In the TKA evaluation, 68% of the patients were female (n=68) and 32% were male (n=32). The mean age was 71 years. Length of stay was 6 days. Pain diminished progressively at discharge/6 months/1 year/2 years (7; 1.8; 1.4 and 1.2), respectively. The ROM progressively increased at discharge/1 month/2 years (82°, 90° and 93°), respectively. The complications rate was 3% (n=3) (fracture and instability). Ambulatory rehabilitation was provided in 8% (n=8). In the THA evaluation, 48% of the patients were female (n=48) and 52% were male (n=52). The mean age was 70 years. Length of stay was 5 days. The complications rate was 3% (n=3) (fracture, dislocation and deep vein thrombosis). Ambulatory rehabilitation was provided in 3% (n=3). In TKA (11 years), the length of stay was 5.96 days, revision surgeries were carried out in 5.96%, and the cost saving in 2013-2015 was 117,776 euros. In THA (11 years), the length of stay was 6.24 days, revision surgeries were performed in 10.62%, and the cost saving in 2013-2015 was 116,316 euros. Conclusions. The implementation/follow-up of the fast-track protocol in THA-TKA was effective in decreasing pain, complications, ambulatory rehabilitation, length of stay, the rate of revision surgery, and costs (AU)

Experimental validation of neutron activation simulation of a varian medical linear accelerator.

This work presents a Monte Carlo simulation using the last version of MCNP, v. 6.1.1, of a Varian CLinAc emitting a 15MeV photon beam. The main objective of the work is to estimate the photoneutron production and activated products inside the medical linear accelerator head. To that, the Varian LinAc head was modelled in detail using the manufacturer information, and the model was generated with a CAD software and exported as a mesh to be included in the particle transport simulation. The model includes the transport of photoneutrons generated by primary photons and the (n, γ) reactions which can result in activation products. The validation of this study was done using experimental measures. Activation products have been identified by in situ gamma spectroscopy placed at the jaws exit of the LinAc shortly after termination of a high energy photon beam irradiation. Comparison between experimental and simulation results shows good agreement.

Neutron distribution and induced activity inside a Linac treatment room.

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.

Evolución del peso del prematuro con alta precoz y atención domiciliaria de enfermería / Influence of in-home nursing care on the weight of the early discharged preterm newborn

INTRODUCCIÓN: La atención domiciliaria de enfermería (ADE) del recién nacido prematuro próximo al alta en su propio domicilio en lugar del hospital normaliza la situación familiar, favorece la lactancia materna y el desarrollo del recién nacido y permite la reorganización de los recursos sanitarios. El propósito del presente trabajo es demostrar que el prematuro sometido al programa de ADE experimenta un aumento de peso superior en el domicilio respecto al hospital y no incrementa su morbilidad. Pacientes y metodología: Estudio comparativo de 65 casos y 65 controles (apareados por peso, edad y sexo), prematuros, de procedencia interna y con peso al alta inferior a 2.100 g. La ADE fue administrada por un pediatra neonatólogo y 2 enfermeras especializadas en neonatología dependientes de los servicios hospitalarios, que realizaron visitas seriadas a domicilio. El aumento de peso se calculó por g/día y g/kg/día, comparando la semana previa al inicio del estudio con la primera semana del estudio. RESULTADOS: Los grupos fueron comparables. El aumento de peso en el grupo con ADE fue de 38 g/día, significativamente superior al del grupo control (31 g/día). Las variables independientes predictoras del «aumento en g/kg/día durante el estudio» fueron la ADE, el sexo varón, tomar menos lactancia materna y no haber padecido una hemorragia peri-intraventricular. La morbilidad neonatal fue similar. CONCLUSIONES: La ADE implicó un mayor aumento de peso del recién nacido en casa que durante su permanencia en el hospital, y no aumentó la morbilidad neonatal

INTRODUCTION: In-Home nursing care of the preterm newborn helps to bring the family situation to normal, promotes breastfeeding and development of the newborn, and enables the reorganization of health care resources. The purpose of this paper is to demonstrate that in-home nursing care of the preterm newborn leads to an increase in weight and a similar morbidity. Patients and methodology: A total of 65 cases and 65 controls (matched by weight, age and sex) were studied, all of them preterm newborns born in hospital and weighing less than 2100 g at discharge. In-home nursing care was carried out by a pediatrician neonatologist, as well as two nurses specialized in neonatology who made several visits to the home. Weight gain was calculated as g/day and g/Kg/day, comparing the first week of the study with the week prior to the beginning of the study. RESULTS: The groups were comparable. Weight gain in the group with home nursing care was 38 g per day, significantly higher than the weight gain in the control group (31 g/day). The independent predictive variables of the increase in g/Kg/day during the study were in-home nursing care, male gender, breastfeeding less, and not having suffered from a peri-intraventricular hemorrhage. Neonatal morbidity was similar in both groups. CONCLUSIONS: In-home care was associated with a greater weight gain of the newborn at home than during their stay in the hospital, and can be considered safe because neonatal morbidity was not increased

[Influence of in-home nursing care on the weight of the early discharged preterm newborn]. / Evolución del peso del prematuro con alta precoz y atención domiciliaria de enfermería.

INTRODUCTION: In-Home nursing care of the preterm newborn helps to bring the family situation to normal, promotes breastfeeding and development of the newborn, and enables the reorganization of health care resources. The purpose of this paper is to demonstrate that in-home nursing care of the preterm newborn leads to an increase in weight and a similar morbidity. PATIENTS AND METHODOLOGY: A total of 65 cases and 65 controls (matched by weight, age and sex) were studied, all of them preterm newborns born in hospital and weighing less than 2100 g at discharge. In-home nursing care was carried out by a pediatrician neonatologist, as well as two nurses specialized in neonatology who made several visits to the home. Weight gain was calculated as g/day and g/Kg/day, comparing the first week of the study with the week prior to the beginning of the study. RESULTS: The groups were comparable. Weight gain in the group with home nursing care was 38 g per day, significantly higher than the weight gain in the control group (31 g/day). The independent predictive variables of the increase in g/Kg/day during the study were in-home nursing care, male gender, breastfeeding less, and not having suffered from a peri-intraventricular hemorrhage. Neonatal morbidity was similar in both groups. CONCLUSIONS: In-home care was associated with a greater weight gain of the newborn at home than during their stay in the hospital, and can be considered safe because neonatal morbidity was not increased.

Neutron activation processes simulation in an Elekta medical linear accelerator head.

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.

Comparison between transmission and scattering spectrum reconstruction methods based on EPID images.

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.

Uncertainty and sensitivity analysis of the effect of the mean energy and FWHM of the initial electron fluence on the Bremsstrahlung photon spectra of linear accelerators.

A calculation of the correct dose in radiation therapy requires an accurate description of the radiation source because uncertainties in characterization of the linac photon spectrum are propagated through the dose calculations. Unfortunately, detailed knowledge of the initial electron beam parameters is not readily available, and many researchers adjust the initial electron fluence values by trial-and-error methods. The main goal of this work was to develop a methodology to characterize the fluence of initial electrons before they hit the tungsten target of an Elekta Precise medical linear accelerator. To this end, we used a Monte Carlo technique to analyze the influence of the characteristics of the initial electron beam on the distribution of absorbed dose from a 6 MV linac photon beam in a water phantom. The technique is based on calculations with Software for Uncertainty and Sensitivity Analysis (SUSA) and Monte Carlo simulations with the MCNP5 transport code. The free parameters used in the SUSA calculations were the mean energy and full-width-at-half-maximum (FWHM) of the initial electron distribution. A total of 93 combinations of these parameters gave initial electron fluence configurations. The electron spectra thus obtained were used in a simulation of the electron transport through the target of the linear accelerator, which produced different photon (Bremsstrahlung) spectra. The simulated photon spectra were compared with the 6-MV photon spectrum provided by the linac manufacturer (Elekta). This comparison revealed how the mean energy and FWHM of the initial electron fluence affect the spectrum of the generated photons. This study has made it possible to fine-tune the examined electron beam parameters to obtain the resulted absorbed doses with acceptable accuracy (error<1%).

MCNP5 Monte Carlo simulation of amorphous silicon EPID dosimetry from MLC radiation therapy treatment beams.

The present work is focused on a MCNP Monte Carlo (MC) simulation of a multi-leaf collimator (MLC) radiation therapy treatment unit including its corresponding Electronic Portal Imaging Device (EPID). We have developed a methodology to perform a spatial calibration of the EPID signal to obtain dose distribution using MC simulations. This calibration is based on several images acquisition and simulation considering different thicknesses of solid water slabs, using a 6 MeV photon beam and a square field size of 20 cm x 20 cm. The resulting relationship between the EPID response and the MC simulated dose is markedly linear. This signal to dose EPID calibration was used as a dosimetric tool to perform the validation of the MLC linear accelerator MCNP model. Simulation results and measurements agreed within 2% of dose difference. The methodology described in this paper potentially offers an optimal verification of dose received by patients under complex multi-field conformal or intensity-modulated radiation therapy (IMRT).

Biological and physical methods for risk estimation in interventional radiology: a detrimental effect approach.

Interventional radiologists and staff members are frequently exposed to the effects of direct and scattered radiation, which undergo in deterministic effects (radiodermitis, aged skin, cataracts, telangiectasia in nasal region, vasocellular epitelioms, hands depilation) and/or stochastic ones (cancer incidence). A methodology has been proposed for estimating the radiation risk or detriment from a group of six exposed interventional radiologists of the Hospital Universitario La Fe (Valencia, Spain), which had developed general exposition symptoms attributable to deterministic effects of ionizing radiation. Equivalent doses have been periodically registered using termoluminiscence dosimeters (TLD's) and wrist dosimeters, H(p)(10) and H(p)(0.07), respectively, and estimated through the observation of translocations in lymphocytes of peripheral blood (biological methods), by extrapolating the yield of translocations to their respective dose-effect curves. The software RADRISK has been applied for estimating radiation risks in these occupational radiation exposures. The minimum and maximum average excess ratio for skin cancer has been, using wrist physical doses, of [1.03 × 10(-3), 5.06 × 10(-2)], concluding that there is not an increased risk of skin cancer incidence. The minimum and maximum average excess ratio for leukemia has been, using TLD physical doses, of [7.84 × 10(-2), 3.36 × 10(-1)], and using biological doses, of [1.40 × 10(-1), 1.51], which is considerably higher than incidence rates, showing an excess radio-induced risk of leukemia in the group under study. Finally, the maximum radiological detriment in the group, evaluated as the total number of radio-induced cancers using physical dosimetry, has been of 2.18 per 1000 person-year (skin and leukemia), and using biological dosimetry of 9.20 per 1000 PY (leukemia). As a conclusion, this study has provided an assessment of the non-deterministic effects (rate of radio-induced cancer incidence) attributable to the group under study due to their professional activity.

6 and 15 MeV photon spectra reconstruction using an unfolding depth dose gradient methodology.

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.

Electron influence on the reconstruction of a linac 6 MeV photon spectra by unfolding methods.

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.

Comparison of experimental 3D dose curves in a heterogeneous phantom with results obtained by MCNP5 simulation and those extracted from a commercial treatment planning system.

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.

Monte Carlo simulation of the iView GT portal imager dosimetry.

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.

3D dose distribution calculation in a voxelized human phantom by means of Monte Carlo method.

The aim of this work is to provide the reconstruction of a real human voxelized phantom by means of a MatLab program and the simulation of the irradiation of such phantom with the photon beam generated in a Theratron 780 (MDS Nordion) (60)Co radiotherapy unit, by using the Monte Carlo transport code MCNP (Monte Carlo N-Particle), version 5. The project results in 3D dose mapping calculations inside the voxelized antropomorphic head phantom. The program provides the voxelization by first processing the CT slices; the process follows a two-dimensional pixel and material identification algorithm on each slice and three-dimensional interpolation in order to describe the phantom geometry via small cubic cells, resulting in an MCNP input deck format output. Dose rates are calculated by using the MCNP5 tool FMESH, superimposed mesh tally, which gives the track length estimation of the particle flux in units of particles/cm(2). Furthermore, the particle flux is converted into dose by using the conversion coefficients extracted from the NIST Physical Reference Data. The voxelization using a three-dimensional interpolation technique in combination with the use of the FMESH tool of the MCNP Monte Carlo code offers an optimal simulation which results in 3D dose mapping calculations inside anthropomorphic phantoms. This tool is very useful in radiation treatment assessments, in which voxelized phantoms are widely utilized.