D Lizio

Università degli Studi di Messina, Messina, Sicily, Italy

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Publications (8)14.65 Total impact

  • E. Amato · D. Lizio · S. Baldari
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    ABSTRACT: The Monte Carlo simulation of particle transport and interaction in matter finds growing applications in medical radiation physics. Dosimetric applications in radiation therapy span from internal dosimetry in radionuclide therapy of nuclear medicine, to the treatment planning in external beam radiation therapy with photons, electrons or fast heavy ions, to the assessment of radiation dose distribution in heterogeneous media such as lungs, bones or renal parenchyma.After a general introduction on the different Monte Carlo packages available (Geant4, Fluka, EGS, MCNP, etc.), we focus on the validation of physical models and parametrizations mostly relevant in the energy range of interest for medical applications, and on the comparison of the outcomes from the various simulation packages.We then report on the recent applications of such packages in the development of new and more accurate models for external beam radiation therapy with photons and electrons, hadron therapy applications, and the internal dosimetry of radionuclides in nuclear medicine treatments. A perspective on the new results in the field of sub-millimeter scale internal dosimetry of tissue and vascular structures will be given, together with a review of the studies on cellular microdosimetry.
    No preview · Article · Mar 2013
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    ABSTRACT: The assessment of radiation absorbed dose is a fundamental issue to plan nuclear medicine therapies with radionuclides. The dose distribution depends on the biokinetics of the radiopharmaceutical and from the physical decay scheme of the radionuclide carried by the molecule. While the physical properties of each nuclide are well known from experimental data, the biodistribution of the radiopharmaceutical within the patient's body depends on the dynamic biologic pathway that, in turn, is governed by the physio-pathologic role of the molecule, by the characteristics of the patient, by the type and stage of the disease, and by the route of administration.The activity distribution must be sampled several times post-administration, by means of planar or tomographic (SPECT or PET) imaging. Tomographic techniques are rapidly substituting planar whole body imaging, since, thanks also to the accurate attenuation correction and image coregistration brought by a simultaneous CT scan, they reach a spatial resolution and an accuracy in activity quantification unprecedented.After a general review on the planar and tomographic image quantification techniques, we focus on the dosimetric models, going from the different anthropomorphic models proposed for the whole human body or specific anatomic districts, to 3D techniques based on voxel dose factors, convolution of dose point-kernels and direct Monte Carlo computation. Particular emphasis will be given to the contribution of Monte Carlo simulation to the development of new and more accurate dosimetric and microdosimetric models for internal dosimetry, especially in relationship with the radiobiological models of the effect of the different particulate radiations employed.We describe the role, specific protocols and obtainable results in the main nuclear medicine therapies such as the 131-I therapy of thyroid diseases, the therapy of neuroendocrine tumors (NET) with somatostatin analogs labeled with beta- or Auger-emitters, and the therapy of non-Hodgkin lymphomas with beta-labeled monoclonal antibodies, focusing on dose-efficacy relationships and on the limiting of side effects to other potentially critical organs.
    No preview · Article · Mar 2013
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    ABSTRACT: Patients candidate to radioiodine treatment of autonomous functioning thyroid nodule (AFTN) are characterized by a wide range of nodule volumes with different shapes. To optimize the treatment, pretherapeutic dosimetry should account also for the dependence of deposited energy on the nodule geometry. We developed a Monte Carlo code in Geant4 to simulate the interaction of beta and gamma radiations emitted by Na-131I into ellipsoidal volumes of soft tissue homogeneously uptaking the radionuclide, surrounded by a simplified antropomorphic phantom. We simulated 9 volumes between 0.1 and 50 cm3, each one with 8 different ellipsoidal shapes. We considered the data of 10 patients affected by AFTN, whose nodule volumes were in the range 1-40 cm3, who underwent radioiodine therapy following the traditional dosimetric approach. The patients underwent ultrasonographic (US) study, in order to determine the nodule volume, and radioiodine thyroid uptake measurements between 3 and 168 hours after radioiodine tracer dose administration. We found an analytical relationship between the average deposited energy and the ellipsoid's semiaxes and we included it in the formula for the calculation of activity to be administered, A0. For the 10 patients studied, A0 calculated with our approach ranges from +9% to -2% with respect to the one calculated with the traditional formula. The proposed model, accounting for the dependence of beta and gamma absorbed fractions from nodule volume and shape, can lead to a more accurate estimation of A0 during AFTN therapy. Since the measurement of nodule axes is routinely obtained from pretherapeutic US, our approach can be introduced in the clinical practice without changing the diagnostic pre-therapeutic protocol.
    No preview · Article · Oct 2011 · The quarterly journal of nuclear medicine and molecular imaging: official publication of the Italian Association of Nuclear Medicine (AIMN) [and] the International Association of Radiopharmacology (IAR), [and] Section of the Society of...
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    E Amato · D Lizio · S Baldari
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    ABSTRACT: We applied a Monte Carlo simulation in Geant4 in order to calculate the absorbed fractions for monoenergetic electrons in the energy interval between 10 keV and 2 MeV, uniformly distributed in ellipsoids made from soft tissue. For each volume, we simulated a spherical shape, four oblate and four prolate ellipsoids, and one scalene shape. For each energy and for every geometrical configuration, an analytical relationship between the absorbed fraction and a 'generalized radius' was found, and the dependence of the fit parameters from electron energy is discussed and fitted by proper parametric functions. With the proposed formulation, the absorbed fraction for electrons in the 10-2000 keV energy range can be calculated for all volumes and for every ellipsoidal shape of practical interest. This method can be directly applied to evaluation of the absorbed fraction from the radionuclide emission of monoenergetic electrons, such as Auger or conversion electrons. The average deposited energy per disintegration in the case of extended beta spectra can be evaluated through integration. Two examples of application to a pure beta emitter such as (90)Y and to (131)I, whose emission include monoenergetic and beta electrons plus gamma photons, are presented. This approach represent a generalization of our previous studies, allowing a comprehensive treatment of absorbed fractions from electron and photon sources uniformly distributed in ellipsoidal volumes of any ellipticity and volume, in the whole range of practical interest for internal dosimetry in nuclear medicine applications, as well as in radiological protection estimations of doses from an internal contamination.
    Full-text · Article · Jan 2011 · Physics in Medicine and Biology
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    ABSTRACT: The objective of this study is to develop a method to calculate the relative dose increase when a computerized tomography scan (CT) is carried out after administration of iodinated contrast medium, with respect to the same CT scan in absence of contrast medium. A Monte Carlo simulation in GEANT4 of anthropomorphic neck and abdomen phantoms exposed to a simplified model of CT scanner was set up in order to calculate the increase of dose to thyroid, liver, spleen, kidneys, and pancreas as a function of the quantity of iodine accumulated; a series of experimental measurements of Hounsfield unit (HU) increment for known concentrations of iodinated contrast medium was carried out on a Siemens Sensation 16 CT scanner in order to obtain a relationship between the increment in HU and the relative dose increase in the organs studied. The authors applied such a method to calculate the average dose increase in three patients who underwent standard CT protocols consisting of one native scan in absence of contrast, followed by a contrast-enhanced scan in venous phase. The authors validated their GEANT4 Monte Carlo simulation by comparing the resulting dose increases for iodine solutions in water with the ones presented in literature and with their experimental data obtained through a Roentgen therapy unit. The relative dose increases as a function of the iodine mass fraction accumulated and as a function of the Hounsfield unit increment between the contrast-enhanced scan and the native scan are presented. The data shown for the three patients exhibit an average relative dose increase between 22% for liver and 74% for kidneys; also, spleen (34%), pancreas (28%), and thyroid (48%) show a remarkable average increase. The method developed allows a simple evaluation of the dose increase when iodinated contrast medium is used in CT scans, basing on the increment in Hounsfield units observed on the patients' organs. Since many clinical protocols employ multiple scans at different circulatory phases after administration of contrast medium, such a method can be useful to evaluate the total dose to the patient, also in view of potential clinical protocol optimizations.
    No preview · Article · Aug 2010 · Medical Physics
  • E Amato · D Lizio · S Baldari
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    ABSTRACT: We studied through Monte Carlo simulation in Geant4 the absorbed fractions for photons, characterized by energies ranging from 10 keV to 1000 keV, which can be emitted by gamma radionuclides uniformly distributed in ellipsoidal volumes of soft tissue. The same analytical relationship between absorbed fraction and the 'generalized radius' as introduced in a previous paper was found, and the dependence of its parameters rho(0) and s on photon energy is discussed and fitted by suitably chosen parametric functions. As a consequence, the absorbed fraction for photons in the 10-1000 keV energy range can be calculated for all volumes and for every ellipsoidal shape of practical interest. Such results can be a useful complement for the dosimetry of beta- and gamma-emitting radionuclides during internal radiotherapy or gamma emitters employed in diagnostic nuclear medicine.
    No preview · Article · Sep 2009 · Physics in Medicine and Biology
  • E Amato · D Lizio · S Baldari
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    ABSTRACT: We developed a Monte Carlo simulation in Geant4 to calculate the absorbed fractions for electrons emitted by (199)Au, (177)Lu, (131)I, (153)Sm, (186)Re and (90)Y, characterized by average energies ranging from 86 keV to 949 keV, uniformly distributed in ellipsoidal volumes of soft tissue. Code validation results with respect to reference data for doses, ranges and absorbed fractions in spheres are presented. An analytical relationship between the absorbed fraction and a 'generalized radius' is introduced in analogy with the transfer function of a first-order high-pass filter, and the dependence of its parameters rho(0) and s from the average electron energy and range is discussed. A generalization for the estimation of absorbed fractions for other radionuclides is also proposed. Such results can be useful to improve accuracy and easiness of calculation in dosimetry during internal radiotherapy.
    No preview · Article · Aug 2009 · Physics in Medicine and Biology
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    E Amato · D Lizio
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    ABSTRACT: We have developed a Monte Carlo simulation in Geant4 to compare the attenuation properties and the bremsstrahlung radiation yield of different types of plastic materials employed as shields for beta- radioactive sources. Code validation results against Sandia and NIST data are presented. For polypropylene (C3H6), polystyrene (C2H3), polyamide nylon-6 (C6H11ON), poly-methyl methacrylate (C5H8O2), polycarbonate (C16H6O3), polyethylene terephthalate (C10H8O4), polyvinyl chloride (C2H3Cl) and polytetrafluoroethylene (C2F4) we evaluated the mean and maximum ranges for electrons originating from 90Sr and 90Y, as well as the number and spectrum of the bremsstrahlung x-rays produced. Significant differences appear between the various materials, and the choice of the best one also depends on the physical properties requested for each specific application.
    Full-text · Article · Jul 2009 · Journal of Radiological Protection