H. Yoriyaz - Academia.edu (original) (raw)

Papers by H. Yoriyaz

Radiation Physics and Chemistry

10th UK Monte Carlo Group …, 2004

A feature recently developed for MCNPX [1] is the ability to perform transmutation calculations. ... more A feature recently developed for MCNPX [1] is the ability to perform transmutation calculations. Although this capability has been available to users via various post-processing utilities, such as Monteburns [2], it would be the first time this process is entirely automated within MCNPX. Such an enhancement provides many benefits to the user by eliminating the need to learn other postprocessing codes, reducing errors in normalizations and auxiliary input, and eliminating file manipulation and tracking issues. This transmutation option is implemented with a batching scheme that updates material properties at various user-specified time steps. The number of particle histories sampled per batch is also specified by the user. Within each time step, MCNPX tallies a 63-group neutron flux averaged over each material within the geometry. At the end of the time step, the neutron flux data and various 1-group cross sections, along with related isotopic atom densities, are passed through an interface routine to CINDER90 [3]. In its usual fashion, CINDER90 uses the neutron fluxes to perform activation, depletion, and decay. It then updates the isotopic inventory, which then is returned to MCNPX for use during transport of the next time step. As usual, users can perform various time-dependent tallies across the entire simulation process. During this first phase of the transmutation implementation, we focus on comparisons between MCNPX and Monteburns. As the MCNPX implementation approaches that of Monteburns, it is expected that the results will be quite similar. For a seven-can HEU configuration, we show that the MCNPX and Monteburns k eff results are within a few percent. While these initial results are encouraging, work continues on understanding the differences (e.g., there are notable differences in the cross sections used by MCNPX and CINDER90).

Nuclear Medicine and Biology, 1999

An in vivo lung tumor model system for radioimmunotherapy of lung metastases was used to test the... more An in vivo lung tumor model system for radioimmunotherapy of lung metastases was used to test the relative effectiveness of the vascular-targeted ␤-particle emitter 90 Y, and ␣-particle emitter, 213 Bi. Yttrium-90 was shown to be stably bound by CHXa؆ DTPA-MAb 201B conjugates and delivered efficiently to lung tumor blood vessels. Dosimetry calculations indicated that the lung received 16.2 Gy/MBq from treatment with 90 Y MAb 201B, which was a sevenfold greater absorbed dose than any other organ examined. Therapy was optimal for 90 Y with 3 MBq injected. Bismuth-213 MAb 201B also delivered a similar absorbed dose (15Gy/MBq) to the lung. Yttrium-90 was found to be slightly more effective against larger tumors than 213 Bi, consistent with the larger range of 2 MeV ␤ particles from 90 Y than the 8 MeV ␣ particles from 213 Bi. Treatment of EMT-6 tumors growing in immunodeficient SCID mice with 90 Y or 213 Bi MAb 201 resulted in significant destruction of tumor colonies; however, 90 Y MAb 201B was toxic for the SCID mice, inflicting acute lung damage. In another tumor model, IC-12 rat tracheal carcinoma growing in SCID mouse lungs, 90 Y therapy was more effective than 213 Bi at destroying lung tumors. However, 90 Y MAb 201B toxicity for the lung limited any therapeutic effect. We conclude that, although vascular-targeted 90 Y MAb can be an effective therapeutic agent, particularly for larger tumors, in this model system, acute damage to the lung may limit its application.

Paper …, 2005

The development of new, sophisticated Monte Carlo codes, and of tomographic or voxel-based human ... more The development of new, sophisticated Monte Carlo codes, and of tomographic or voxel-based human phantoms motivated the International Commission on Radiological Protection (ICRP) to call for a revision of traditional exposure models, which have been used in the past to calculate organ and tissue as well as effective dose coefficients for stylized MIRD5-type phantoms. This paper reports about calculations made with the recently developed tomographic MAX (Male Adult voXel) and FAX (Female Adult voXel) phantoms, as well as with the gender-specific MIRD5-type phantoms ADAM and EVA, coupled to the EGS4 and to the MCNP4C Monte Carlo code, for external whole-body irradiation with electrons. Effective doses for the tomographic and for the stylized exposure models will be compared separately as function of the replacement of the Monte Carlo code, of human tissue compositions, and of the stylized by the tomographic anatomy. The results indicate that for external exposures to electrons the introduction of voxel-based exposure models causes changes of the effective dose between +40% and-60% depending on the energies and geometries considered compared to corresponding data of the MIRD5-type phantoms.

O metodo de Monte Carlo tem se tornado, ao longo dos anos, uma ferramenta padrao para calculos de... more O metodo de Monte Carlo tem se tornado, ao longo dos anos, uma ferramenta padrao para calculos de dose absorvida e outras grandezas de interesse nas areas de terapeutica e diagnostico da Fisica Medica. Este artigo faz uma breve revisao das principais aplicacoes deste metodo, abrangendo as aplicacoes nas diversas modalidades de tratamento, acompanhado da descricao do surgimento dos principais codigos computacionais. Com o intuito de introduzir o tema aqueles que desejam conhecer o metodo, e apresentada uma breve descricao dos conceitos basicos do metodo e suas potencialidades.

Objectives: Patient-specific dosimetry methods using the SCMS software tool (that provides input ... more Objectives: Patient-specific dosimetry methods using the SCMS software tool (that provides input for the MCNP radiation transport simulation code from three dimensional patient image data sets) have been extended using image-based segmentation tools. A user interface has been developed to streamline the processing of data. The objective of this study is to assess the capabilities of these tools in handling phantom and patient data sets taken from a CT-SPECT dual head gamma camera system. Methods: The SCMS software was installed on Vanderbilt University Medical Center Unix-based machines running the MCNP code. An image-based segmentation tool was written in IDL, which uses CT or MR images to define anatomical structures and SPECT or PET data to establish activity distributions within these structures. Organ identifiers are tied to those established for the Zubal et al. voxel phantom, as is the basis for the SCMS routines. Other IDL routines provide file conversion and other utilities...

Journal of nuclear medicine : official publication, Society of Nuclear Medicine, 1999

UNLABELLED A revised geometric representative model of the lower part of the colon, including the... more UNLABELLED A revised geometric representative model of the lower part of the colon, including the rectum, the urinary bladder and prostate, is proposed for use in the calculation of absorbed dose from injected radiopharmaceuticals. The lower segment of the sigmoid colon as described in the 1987 Oak Ridge National Laboratory mathematical phantoms does not accurately represent the combined urinary bladder/rectal/prostate geometry. In the revised model in this study, the lower part of the abdomen includes an explicitly defined rectum. The shape of sigmoid colon is more anatomically structured, and the diameters of the descending colon are modified to better approximate their true anatomic dimensions. To avoid organ overlap and for more accurate representation of the urinary bladder and the prostate gland (in the male), these organs are shifted from their originally defined positions. The insertion of the rectum and the shifting of the urinary bladder will not overlap with or displace t...

This work presents a series of simulations run to evaluate the response of a neutron coincidence ... more This work presents a series of simulations run to evaluate the response of a neutron coincidence collar employed in safe guard experiments of fresh fuel control. Simulations were performed using MCNP code and were restricted to 2 different PWR fuel assemblies, one of then with 6 distinct configurations. A simulation approach was implemented in a way that coincidence counting was circumvented. The obtained results show good qualitative agreement with published experimental data.

Journal of Nuclear Medicine, 2001

This study was intended to verify the capability of the Monte Carlo MCNP-4B code to evaluate spat... more This study was intended to verify the capability of the Monte Carlo MCNP-4B code to evaluate spatial dose distribution based on information gathered from CT or SPECT.

With the evolution of radiation therapy techniques, treatments have become increasingly accurate.... more With the evolution of radiation therapy techniques, treatments have become increasingly accurate. To ensure a good quality assurance program for modern equipment, Sun Nuclear Corporation has developed ArcCHECK, a 3D dosimetric system, which contains 1386 helically arranged diodes within a PMMA cylindrical structure. The outputs of this system show, in addition to dose values acquired directly from the diodes, also matrices with interpolated dose values, in order to provide values at more than 5000 points for quality assurance. The main purpose of this work is to analyze the interpolated dose values provided by ArcCHECK. For this, simple measurements were taken with ArcCHECK, with a 10x10 cm static field of 6 MeV photons and 100 MU. A algorithm for MATLAB software was also developed so that it was possible to interpolate crude dose values obtained from the diodes and compare them with the values interpolated by the dosimetric system software. Significant dose differences values were ...

A great challenge in simulations in the area of radiotherapy is to character the source, since th... more A great challenge in simulations in the area of radiotherapy is to character the source, since the equipment’s manufacturers don’t provide specifics information about this. This work presents an empiric method for characterization of the ray-X beams of 6,0 MV and 10 MV originating from a linear accelerator of the mark Varian model 2100C. The experimental values of the percentage of deep dose (PDD) were used for reconstruction of the energy spectrum and analysis of the angular distribution of the beam simulated with Monte Carlo's Method, using the code MCNP-4C. The results were shown solid could be used for the space reconstruction of the beam. Keywords— PDD reconstruction, Monte Carlo method, MCNP, medical physics.

Radiotherapy and Oncology, 2020

The Expectation-Maximization (E-M) algorithm is an iterative computational method for maximum lik... more The Expectation-Maximization (E-M) algorithm is an iterative computational method for maximum likelihood (M-L) estimates, useful in a variety of incomplete-data problems. Due to its stochastic nature, one of the most relevant applications of E-M algorithm is the reconstruction of emission tomography images. In this paper, the statistical formulation of the E-M algorithm was applied to the in vivo spectrographic imaging of stable isotopes called Neutron Stimulated Emission Computed Tomography (NSECT). In the process of E-M algorithm iteration, the conditional probability distribution plays a very important role to achieve high quality image. This present work proposes an alternative methodology for the generation of the conditional probability distribution associated to the E-M reconstruction algorithm, using the Monte Carlo code MCNP5 and with the application of the reciprocity theorem. The Expectation-Maximization (E-M) algorithm is a generally used approach to the iterative comput...

UNLABELLED This study was intended to verify the capability of the Monte Carlo MCNP-4B code to ev... more UNLABELLED This study was intended to verify the capability of the Monte Carlo MCNP-4B code to evaluate spatial dose distribution based on information gathered from CT or SPECT. METHODS A new three-dimensional (3D) dose calculation approach for internal emitter use in radioimmunotherapy (RIT) was developed using the Monte Carlo MCNP-4B code as the photon and electron transport engine. It was shown that the MCNP-4B computer code can be used with voxel-based anatomic and physiologic data to provide 3D dose distributions. RESULTS This study showed that the MCNP-4B code can be used to develop a treatment planning system that will provide such information in a time manner, if dose reporting is suitably optimized. If each organ is divided into small regions where the average energy deposition is calculated with a typical volume of 0.4 cm(3), regional dose distributions can be provided with reasonable central processing unit times (on the order of 12-24 h on a 200-MHz personal computer or ...

Since the beginning of its use, radiation has already presented harm, justifying the necessity of... more Since the beginning of its use, radiation has already presented harm, justifying the necessity of controlled use. In order to monitor its effects and even avoid them, dosimetry has arisen. For the purpose of ensured all the necessary safety and monitor areas where there is radiation use, a lot of devices able to identify and quantify many types of radiation were developed. However, some these dosimeters are more widely used today like ionizing chamber, chemical dosimeters, photographic dosimeters and thermoluminescent dosimeters (TLD). When a group of TLD is obtained with a quantity n of dosimeters, there is a variation of answer of these dosimeters when they are subjected to the same irradiations conditions, from this comes the importance of individual calibration of these, to select the dosimeters with close answers, reducing the uncertainties of the measures. Therefore, this work presents the calculation of correction factors for the TLD of lithium fluoride (LiF-100) and shows ho...

Revista Brasileira de Física Médica

Com a evolução dos sistemas de planejamento e a redução das incertezas no cálculo de dose, a corr... more Com a evolução dos sistemas de planejamento e a redução das incertezas no cálculo de dose, a correção de heterogeneidades se tornou necessária. A presença de ligas metálicas de alta densidade ainda é uma das limitações e fonte de imprecisão no cálculo de dose. Embora existam algoritmos de cálculo de dose precisos, a principal dificuldade está no estabelecimento de curvas de correção do número de Hounsfield (HU) para densidade eletrônica (CT-to-ED), para valores de HU apropriados. A maioria dos tomógrafos atuais trabalha com 12 bits, saturando o número de Hounsfield em torno de 3000 HU sendo insuficiente para a maioria dos materiais de alta densidade. No entanto, já existem equipamentos em 16 bits, que não saturam na presença de materiais de alto número atômico (Z) e resultam em informações mais completas das propriedades físicas. O objetivo deste trabalho é avaliar, em irradiações de heterogeneidades de alto Z, o impacto dosimétrico quando são utilizadas curvas de correção que inclu...