David Broggio

Construction of an extended library of adult male 3D models: rationale and results.

In order to best cover the possible extent of heights and weights of male adults the construction of 25 whole body 3D models has been undertaken. Such a library is thought to be useful to specify the uncertainties and relevance of dosimetry calculations carried out with models representing individuals of average body heights and weights. Representative 3D models of Caucasian body types are selected in a commercial database according to their height and weight, and 3D models of the skeleton and internal organs are designed using another commercial dataset. A review of the literature enabled one to fix volume or mass target values for the skeleton, soft organs, skin and fat content of the selected individuals. The composition of the remainder tissue is fixed so that the weight of the voxel models equals the weight of the selected individuals. After mesh and NURBS modelling, volume adjustment of the selected body shapes and additional voxel-based work, 25 voxel models with 109 identified organs or tissue are obtained. Radiation transport calculations are carried out with some of the developed models to illustrate potential uses. The following points are discussed throughout this paper: justification of the fixed or obtained models’ features regarding available and relevant literature data; workflow and strategy for major modelling steps; advantages and drawbacks of the obtained library as compared with other works. The construction hypotheses are explained and justified in detail since future calculation results obtained with this library will depend on them.

Treatment plans optimization for contrast-enhanced synchrotron stereotactic radiotherapy.

PURPOSEnSynchrotron stereotactic radiotherapy (SSRT) is a treatment that involves the targeting of high-Z elements into tumors followed by stereotactic irradiation with monochromatic x-rays from a synchrotron source, tuned at an optimal energy. The irradiation geometry, as well as the secondary particles generated at a higher yield by the medium energy x-rays on the high-Z atoms (characteristic x-rays, photoelectrons, and Auger electrons), produces a localized dose enhancement in the tumor. Iodine-enhanced SSRT with systemic injections of iodinated contrast agents has been successfully developed in the past six years in the team, and is currently being transferred to clinical trials. The purpose of this work is to study the impact on the SSRT treatment of the contrast agent type, the beam quality, the irradiation geometry, and the beam weighting for defining an optimized SSRT treatment plan.nnnMETHODSnTheoretical dosimetry was performed using theMCNPX particle transport code. The simulated geometry was an idealized phantom representing a human head. A virtual target was positioned in the central part of the phantom or off-centered by 4 cm. The authors investigated the dosimetric characteristics of SSRT for various contrast agents: Iodine, gadolinium, and gold; and for different beam qualities: Monochromatic x-ray beams from a synchrotron source (30-120 keV), polychromatic x-ray beams from an x-ray tube (80, 120, and 180 kVp), and a 6 MV x-ray beam from a linear accelerator. Three irradiation geometries were studied: One arc or three noncoplanar arcs dynamic arc therapy, and an irradiation with a finite number of beams. The resulting dose enhancements, beam profiles, and histograms dose volumes were compared for iodine-enhanced SSRT. An attempt to optimize the irradiation scheme by weighing the finite x-ray beams was performed. Finally, the optimization was studied on patient specific 3D CT data after contrast agent infusion.nnnRESULTSnIt was demonstrated in this study that an 80 keV beam energy was a good compromise for treating human brain tumors with iodine-enhanced SSRT, resulting in a still high dose enhancement factor (about 2) and a superior bone sparing in comparison with lower energy x-rays. This beam could easily be produced at the European Synchrotron Radiation Facility medical beamline. Moreover, there was a significant diminution of dose delivered to the bone when using monochromatic x-rays rather than polychromatic x-rays from a conventional tube. The data showed that iodine SSRT exhibits a superior sparing of brain healthy tissue in comparison to high energy treatment. The beam weighting optimization significantly improved the treatment plans for off-centered tumors, when compared to nonweighted irradiations.nnnCONCLUSIONSnThis study demonstrated the feasibility of realistic clinical plans for low energy monochromatic x-rays contrast-enhanced radiotherapy, suitable for the first clinical trials on brain metastasis with a homogeneous iodine uptake.

Early detection and prediction of cardiotoxicity after radiation therapy for breast cancer: the BACCARAT prospective cohort study

BackgroundRadiotherapy (RT) for breast cancer presents a benefit in terms of reducing local recurrence and deaths resulting from breast cancer but it can lead to secondary effects due to the presence of neighboring cardiac normal tissues within the irradiation field. Breast RT has been shown to be associated with long-term increased risk of heart failure, coronary artery disease, myocardial infarction and finally cardiovascular death more than 10xa0years after RT. However, there is still a lack of knowledge for early cardiotoxicity induced by breast RT that can appear long before the onset of clinically significant cardiac events. Based on a 2-year follow-up prospective cohort of patients treated with breast RT, the BACCARAT (BreAst Cancer and CArdiotoxicity Induced by RAdioTherapy) study aims to enhance knowledge on detection and prediction of early subclinical cardiac dysfunction and lesions induced by breast RT and on biological mechanisms potentially involved, based on functional and anatomical cardiac imaging combined with simultaneous assessment of multiple circulating biomarkers and accurate heart dosimetry.Methods/DesignBACCARAT study consists in a monocentric prospective cohort study that will finally include 120 women treated with adjuvant 3D CRT for breast cancer, and followed for 2xa0years after RT. Women aged 50 to 70xa0years, treated for breast cancer and for whom adjuvant 3D CRT is indicated, without chemotherapy are eligible for the study. Baseline (before RT) and follow-up data include measurements of functional myocardial dysfunction including strain and strain rate based on 2D-speckle tracking echocardiography, anatomical coronary lesions including description of plaques in segments of coronary arteries based on Coronary computed tomography angiography, and a wide panel of circulating biomarkers. The absorbed dose is evaluated for the whole heart and its substructures, in particular the coronary arteries. Analysis on occurrence and evolution of subclinical cardiac lesions and biomarkers will be performed and completed with dose-response relationship. Multivariate model of normal tissue complication probability (NTCP) will also be proposed.DiscussionTools and results developed in the BACCARAT study should allow improving prediction and prevention of potential lesions to cardiac normal tissues surrounding tumors and ultimately enhance patients’ care and quality of life.Trial registrationClinicalTrials.gov: NCT02605512

Examples of Mesh and NURBS modelling for in vivo lung counting studies

Realistic calibration coefficients for in vivo counting installations are assessed using voxel phantoms and Monte Carlo calculations. However, voxel phantoms construction is time consuming and their flexibility extremely limited. This paper involves Mesh and non-uniform rational B-splines graphical formats, of greater flexibility, to optimise the calibration of in vivo counting installations. Two studies validating the use of such phantoms and involving geometry deformation and modelling were carried out to study the morphologic effect on lung counting efficiency. The created 3D models fitted with the reference ones, with volumetric differences of <5 %. Moreover, it was found that counting efficiency varies with the inverse of lungs volume and that the latter primes when compared with chest wall thickness. Finally, a series of different thoracic female phantoms of various cup sizes, chest girths and internal organs volumes were created starting from the International Commission on Radiological Protection (ICRP) adult female reference computational phantom to give correction factors for the lung monitoring of female workers.

Coronary stenosis risk analysis following Hodgkin lymphoma radiotherapy: A study based on patient specific artery segments dose calculation

BACKGROUND AND PURPOSEnThe dose effect-effect relationship for cardiac diseases following radiotherapy suffers from uncertainties. Three dimensional coronary artery (CA) dose calculation after mediastinal Hodgkin lymphoma radiotherapy was performed, using the patients coronary CT angiography (CCTA), and the relationship between the coronary arteries radiation doses and the risk of stenosis was estimated.nnnMATERIALS AND METHODSnRadiotherapy simulation CT scans and CCTAs of patients treated for a mediastinal Hodgkin lymphoma were used to merge thoracic and detailed cardiovascular anatomies. Radiation treatment parameters were used to estimate CA radiation doses. Twenty-one patients without coronary stenosis (controls) were matched with twelve patients with stenosis (cases). CA segments were considered as sub-volumes of interest. Radiation doses to stenotic segments were compared with those received by normal segments (from cases and controls) using a logistic regression.nnnRESULTSnIn eleven cases out of twelve, the highest of the coronary dose distribution was on a damaged segment. Logistic regression with CA segments yielded an odds ratio associated with the risk of coronary stenosis of 1.049 per additional gray with the CA segment median dose (95% confidence interval, 1.004-1.095; p-value <0.05).nnnCONCLUSIONnThe CA segment dose significantly increased the risk of stenosis on the segment. Such personalized CA dose calculations on larger cohorts are expected to improve the understanding of the cardiovascular radiation dose-effect relationship.

Creation and use of adjustable 3D phantoms: application for the lung monitoring of female workers.

In vivo counting measurements, used for the monitoring of workers with internal contamination risks, are based on the use of calibration physical phantoms. However, such phantoms do not exist for female subjects. Computational calibration using numerical representations, Mesh and non-uniform rational basis spline (NURBS) geometries, was thus considered. The study presented here is focused on the creation of different female thoracic phantoms with various breast sizes and chest girths. These 3D models are used to estimate the radiation attenuation with morphology and the resulting variation of the calibration coefficient of a typical 4-germanium in vivo counting system. A basic Mesh female thoracic phantom was created from the International Commission on Radiological Protection Adult Female Reference Computational Phantom. Using this basic phantom, different chest girths (85, 90, 100, 110, and 120) and cup sizes (A to F) were created representing the most common thoracic female morphologies, as recommended by the available and relevant literature. Variation of breast tissue composition and internal organ volumes with morphology were also considered. As a result, 34 thoracic female phantoms were created combining different cup sizes and chest girths. For the 85 chest girth, at very low energies (15 keV), a relative counting efficiency variation of about 85% was observed between the A and E cups. As a result of this study, breast size dependent calibration coefficients, between 15 keV and 1.4 MeV, were obtained and tabulated for a typical lung counting germanium system.

EURADOS intercomparison on measurements and Monte Carlo modelling for the assessment of americium in a USTUR leg phantom

A collaboration of the EURADOS working group on Internal Dosimetry and the United States Transuranium and Uranium Registries (USTUR) has taken place to carry out an intercomparison on measurements and Monte Carlo modelling determining americium deposited in the bone of a USTUR leg phantom. Preliminary results and conclusions of this intercomparison exercise are presented here.

Female workers and in vivo lung monitoring: a simple model for morphological dependence of counting efficiency curves

This paper addresses the question of the morphological dependence of counting efficiency curves for in vivo lung monitoring of workers, with a particular focus on the case of female workers for whom different chest girth and cup size are considered. A library of 24 female torsos, with chest girth varying from 85 to 120 and cup size from A to F, was constructed using mesh and NURBS formats. The anatomical realism and usefulness of these models for simulating in vivo counting measurements are illustrated and simulations are reported for a typical 4-germanium (Ge) counting system. A simple analytic formula describing the relation between efficiency curves obtained for each female phantom is given. This formula uses the mass attenuation coefficient for adipose tissue and two parameters which are dependant on lung volume and breast weight. The model is tested against Monte Carlo simulated data, experimental data obtained with the Livermore phantom and published data. The model correctly describes the efficiency curve and, since the parameters depend on the counting geometry, it is shown how to estimate them from experimental measurements.

Study of the Influence of Radionuclide Biokinetics on the Efficiency of In Vivo Counting Using Monte Carlo Simulation

To improve calibration methods of in vivo counting, our laboratory has developed a computer tool to model internal contamination and assess in vivo activity and corresponding organ absorbed doses. The aim of the recent work was to define a more realistic source based on biokinetic models. The influence of the biokinetic parameters on the in vivo counting was studied through the simulation of an acute inhalation intake of 241Am. The tissue distribution of activity predicted by the biokinetic model was visualized. Two equivalent methods for determination of the efficiency related to the total activity distributed in the body were used. The comparison between the efficiency taking the biokinetics into account and the classically estimated efficiency quantifies the influence of the activity distribution in the body and provides conversion factors for correcting the classical efficiency to account for biokinetics.

Analytical and Monte Carlo assessment of activity and local dose after a wound contamination by activation products.

The activity and local dose following a right index finger wound contamination by activation products are assessed. Measurements with a high purity germanium detector and a four positions measurement protocol enabled a better localization of the contaminant source. From the source location and detector calibration, the remaining wound activity and local absorbed dose were deduced. An analytical model, based on a two dimensional simplification of the problem, is presented. It is shown to provide a fast and quite accurate activity assessment when the contaminants are described as a point source. The contaminants location and activity were then more accurately assessed using Monte Carlo calculations based on the OEDIPE software and a voxelized phantom of the index finger. Describing the contaminant mixture as a point source resulted in an agreement of experimental and computed data around 6% for most of the radionuclides. The total activity, due to 11 radionuclides, was estimated to be (9.5 ± 0.4) kBq at measurement day. Since the point source is found to be less than 1 mm under the skin, the equivalent skin dose is calculated and found to be around 680 mSv in the first year after the contamination, and this value decreases to 250 mSv in the second year. The relevance of equivalent skin dose as an estimate of the sanitary risk is discussed, and it is concluded that for this case it gives the upper end estimate of the risk.