X G Xu

Publications (18)27.9 Total impact

• Source

  Available from: rpi.edu

  Article: X-ray imaging optimization using virtual phantoms and computerized observer modelling.

  I-Y Son, M Winslow, B Yazici, X G Xu
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  ABSTRACT: This study develops and demonstrates a realistic x-ray imaging simulator with computerized observers to maximize lesion detectability and minimize patient exposure. A software package, ViPRIS, incorporating two computational patient phantoms, has been developed for simulating x-ray radiographic images. A tomographic phantom, VIP-Man, constructed from Visible Human anatomical colour images is used to simulate the scattered portion using the ESGnrc Monte Carlo code. The primary portion of an x-ray image is simulated using the projection ray-tracing method through the Visible Human CT data set. To produce a realistic image, the software simulates quantum noise, blurring effects, lesions, detector absorption efficiency and other imaging artefacts. The primary and scattered portions of an x-ray chest image are combined to form a final image for computerized observer studies and image quality analysis. Absorbed doses in organs and tissues of the segmented VIP-Man phantom were also obtained from the Monte Carlo simulations. Approximately 25,000 simulated images and 2,500,000 data files were analysed using computerized observers. Hotelling and Laguerre-Gauss Hotelling observers are used to perform various lesion detection tasks. Several model observer tasks were used including SKE/BKE, MAFC and SKEV. The energy levels and fluence at the minimum dose required to detect a small lesion were determined with respect to lesion size, location and system parameters.
  Physics in Medicine and Biology 10/2006; 51(17):4289-310. · 2.83 Impact Factor
• Article: Four-dimensional human modeling for respiratory motion and the impact on radiation treatment planning

  J. Y. Zhang, X. G. Xu, C. Y. Shi
  Chin J Med Imaging Technol. 01/2006; 22:1301-1305.
• Conference Proceeding: Issues related to the use of MCNP code for an extremely large voxel model VIP-Man

  B. Wang, X. G. Xu, J. T. Goorley, A. Bozkurt
  01/2005
• Article: Specific absorbed fractions for internal photon emitters calculated for a tomographic model of a pregnant woman.

  C Y Shi, X G Xu, M G Stabin
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  ABSTRACT: Specific absorbed fractions are essential for calculation of radiation dose from internal emitters. Existing specific absorbed fractions for pregnant women were calculated using the stylized models; in this work, a partial-body tomographic model for a pregnant woman was constructed from a rare set of CT images. Based on this tomographic model, the Monte Carlo code, EGS4-VLSI, was used to derive specific absorbed fractions. Monoenergetic, isotropic photon emitters from 15 keV to 4 MeV were distributed in different source organs, and doses were calculated to many target regions in the body. Even though the results showed general agreement with previous studies for higher energies, significant differences were also found, especially for lower energies. The main reasons for the differences are due to the variation of mass, geometry, and organ distances, and they demonstrate the influence of more realistic body models on dose calculations.
  Health Physics 12/2004; 87(5):507-11. · 1.68 Impact Factor
• Article: Fluence-to-dose conversion coefficients for monoenergetic proton beams based on the VIP-Man anatomical model.

  A Bozkurt, X G Xu
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  ABSTRACT: A new set of fluence-to-absorbed dose and fluence-to-effective dose conversion coefficients has been calculated for high-energy protons using the whole-body anatomical model VIP-Man, which was developed from the high-resolution transverse colour photographic images of the National Library of Medicine's Visible Human Project. For 10 monoenergetic proton beams between 20 and 10,000 MeV, organ dose calculations were performed using the Monte Carlo code MCNPX under six different irradiation geometries: anterior-posterior, posterior-anterior, left lateral, right lateral, isotropic and rotational. The absorbed dose results for 24 major organs of VIP-Man are presented and compared with those based on mathematical phantoms reported in the literature. The discrepancies (generally within 40%) in organ dose and effective dose estimates are attributed to the use of different transport models employed by different Monte Carlo codes.
  Radiation Protection Dosimetry 02/2004; 112(2):219-35. · 0.82 Impact Factor
• Article: Calculations of specific absorbed fractions of the gastrointestinal tract using a realistic whole body tomographic model.

  X G Xu, T C Chao
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  ABSTRACT: Assessment of organ doses from internally deposited radionuclides involves the use of predetermined specific absorbed fractions (SAFs). Many tabulations of SAFs have been derived from Monte Carlo transport simulations using stylized computational models that are not fully realistic of human internal organ anatomy. This paper presents the results of a study to calculate SAFs in the gastrointestinal (GI) tract using a recently developed tomographic model VIP-Man and the EGS4 Monte Carlo radiation transport code. Results show that, for some energies and source-target combinations, considerable discrepancies exist between these results and those from earlier studies, suggesting a need to evaluate existing data carefully by comparison with realistic models.
  Cancer Biotherapy and Radiopharmaceuticals 07/2003; 18(3):431-6. · 1.79 Impact Factor
• Article: Estimating the depth of embedded contaminants from in-situ gamma spectroscopic measurements.

  A Al-Ghamdi, X G Xu
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  ABSTRACT: The depth of radiological contamination is information required for decontamination and decommissioning of nuclear facilities. This paper proposes and tests a simple technique for measuring the depth of contamination. The method uses measurements with an HPGe detector at two distances (or heights) from the surface on the same side of the medium. The ratio of the photopeak areas easily can be used to yield the depth of an embedded source. The calculational algorithm was verified by simulations with the MCNP4C code and laboratory experiments for a point source and other special sources. Predictions of the depth for shallowly embedded sources have relatively large uncertainties (approximately 18%) but improve as depth increases. This technique provides a very easy way for a user to quickly estimate the depth of the subsurface contamination on site.
  Health Physics 06/2003; 84(5):632-6. · 1.68 Impact Factor
• Article: Fluence-to-dose conversion coefficients based on the VIP-Man anatomical model and MCNPX code for monoenergetic neutrons above 20 MeV.

  A Bozkurt, T C Chao, X G Xu
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  ABSTRACT: A new set of fluence-to-absorbed dose and fluence-to-effective dose conversion coefficients has been calculated for high-energy neutrons using a whole-body anatomical model, VIP-Man, developed from the high-resolution transversal color photographic images of the National Library of Medicine's Visible Human Project. Organ dose calculations were performed using the Monte Carlo code MCNPX for 20 monoenergetic neutron beams between 20 MeV and 10,000 MeV under 6 different irradiation geometries: anterior-posterior, posterior-anterior, left lateral, right lateral, isotropic, and rotational. For neutron Monte Carlo calculations, results based on an image-based whole-body model were not available in the literature. The absorbed dose results for 24 major organs of VIP-Man are presented in the form of tables and selected figures that compare with those based on simplified mathematical phantoms reported in the literature. VIP-Man yields up to 40% larger values of effective dose and many organ doses, thus suggesting that the results reported in the past may not be conservative.
  Health Physics 09/2001; 81(2):184-202. · 1.68 Impact Factor
• Article: Conversion coefficients based on the VIP-Man anatomical model and EGS4.

  T C Chao, A Bozkurt, X G Xu
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  ABSTRACT: A new set of conversion coefficients from kerma free-in-air to absorbed dose and kerma free-in-air to "effective VIP-Man dose" has been calculated for external monoenergetic photon beams from 10 keV to 10 MeV using an image-based whole-body anatomical model. This model, called VIP-Man, was recently developed at Rensselaer from the high-resolution color images of the National Library of Medicine's Visible Human Project. An EGS4-based Monte Carlo user code, named EGS4-VLSI, was developed to efficiently process the extremely large image data in VIP-Man. Irradiation conditions include anterior-posterior, posterior-anterior, right lateral, left lateral, rotational, and isotropic geometries. Conversion coefficients from this study are compared with those obtained from two mathematical models, ADAM and EVA. "Effective VIP-Man doses" differ from the previously reported effective dose results by 10%-50% for photons between 100 keV and 10 MeV. Discrepancies are more significant at lower energies and for individual organ doses. Since VIP-Man is a realistic model that contains several tissues that were not previously defined well (or not available) in other models, the reported results offer an opportunity to improve the existing dosimetric data and the mathematical models.
  Health Physics 09/2001; 81(2):163-83. · 1.68 Impact Factor
• Article: Organ dose conversion coefficients for 0.1-10 MeV electrons calculated for the VIP-Man tomographic model.

  T C Chao, A Bozkurt, X G Xu
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  ABSTRACT: A whole-body tomographic model, called VIP-Man, was recently developed at Rensselaer Polytechnic Institute from the high-resolution color photographic images of the National Library of Medicine's Visible Human Project. An EGS4-based Monte Carlo user code, named EGS4-VLSI, was developed to efficiently transport electrons using the large image data set for VIP-Man. VIP-Man has been used to calculate doses for neutrons and photons. This paper presents a new set of fluence-to-absorbed-dose conversion coefficients for monoenergetic electron beams between 100 keV and 10 MeV for VIP-Man. Irradiation conditions include anterior-posterior, posterior-anterior, right lateral, left lateral, rotational, and isotropic source geometries. Comparisons between organ doses from VIP-Man, which is taller and heavier than the Reference Man, and existing data from mathematical models show significant discrepancies. It appears that even slight differences between body models can cause dramatic dosimetric deviations for low penetrating electron irradiation. This suggests that a single standard body model may poorly represent a large population and may not be acceptable for electron dosimetry.
  Health Physics 09/2001; 81(2):203-14. · 1.68 Impact Factor
• Article: CONVERSION COEFFICIENTS BASED ON THE VIP-MAN ANATOMICAL MODEL AND EGS4-VLSI CODE FOR EXTERNAL MONOENERGETIC PHOTONS FROM 10 keV TO 10 MeV

  T. C. Chao, A. Bozkurt, X. G. Xu
  [show abstract] [hide abstract]
  ABSTRACT: A new set of conversion coefficients from kerma free-in-air to absorbed dose and kerma free-in-air to effective VIP-Man dose has been calculated for external monoenergetic photon beams from 10 keV to 10 MeV using an image-based whole-body anatomical model. This model, called VIP-Man, was recently developed at Rensselaer from the high-resolution color images of the National Library of Medicine's Visible Human Project. An EGS4-based Monte Carlo user code, named EGS4-VLSI, was developed to efficiently process the extremely large image data in VIP-Man. Irradiation conditions include anterior-posterior, posterior-anterior, right lateral, left lateral, rotational, and isotropic geometries. Conversion coefficients from this study are compared with those obtained from two mathematical models, ADAM and EVA. "Effective VIP-Man doses" differ from the previously reported effective dose results by 10%-50% for photons between 100 keV and 10 MeV. Discrepancies are more significant at lower energies and for individual organ doses. Since VIP-Man is a realistic model that contains several tissues that were not previously defined well (or not available) in other models, the reported results offer an opportunity to improve the existing dosimetric data and the mathematical models. (C)2001Health Physics Society
  Health Physics 07/2001; 81(2). · 1.68 Impact Factor
• Article: Specific absorbed fractions from the image-based VIP-Man body model and EGS4-VLSI Monte Carlo code: internal electron emitters.

  T C Chao, X G Xu
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  ABSTRACT: VIP-Man is a whole-body anatomical model newly developed at Rensselaer from the high-resolution colour images of the National Library of Medicine's Visible Human Project. This paper summarizes the use of VIP-Man and the Monte Carlo method to calculate specific absorbed fractions from internal electron emitters. A specially designed EGS4 user code, named EGS4-VLSI, was developed to use the extremely large number of image data contained in the VIP-Man. Monoenergetic and isotropic electron emitters with energies from 100 keV to 4 MeV are considered to be uniformly distributed in 26 organs. This paper presents, for the first time, results of internal electron exposures based on a realistic whole-body tomographic model. Because VIP-Man has many organs and tissues that were previously not well defined (or not available) in other models, the efforts at Rensselaer and elsewhere bring an unprecedented opportunity to significantly improve the internal dosimetry.
  Physics in Medicine and Biology 05/2001; 46(4):901-27. · 2.83 Impact Factor
• Article: Fluence-to-dose conversion coefficients from monoenergetic neutrons below 20 MeV based on the VIP-man anatomical model.

  A Bozkurt, T C Chao, X G Xu
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  ABSTRACT: A new set of fluence-to-absorbed dose and fluence-to-effective dose conversion coefficients have been calculated for neutrons below 20 MeV using a whole-body anatomical model, VIP-Man, developed from the high-resolution transverse colour photographic images of the National Library of Medicine's Visible Human Project. Organ dose calculations were performed using the Monte Carlo code MCNP for 20 monoenergetic neutron beams between 1 x 10(-9) MeV and 20 MeV under six different irradiation geometries: anterior-posterior, posterior-anterior, right lateral, left lateral, rotational and isotropic. The absorbed dose for 24 major organs and effective dose results based on the realistic VIP-Man are presented and compared with those based on the simplified MIRD-based phantoms reported in the literature. Effective doses from VIP-Man are not significantly different from earlier results for neutrons in the energy range studied. There are, however, remarkable deviations in organ doses due to the anatomical differences between the image-based and the earlier mathematical models.
  Physics in Medicine and Biology 11/2000; 45(10):3059-79. · 2.83 Impact Factor
• Article: VIP-Man: an image-based whole-body adult male model constructed from color photographs of the Visible Human Project for multi-particle Monte Carlo calculations.

  X G Xu, T C Chao, A Bozkurt
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  ABSTRACT: Human anatomical models have been indispensable to radiation protection dosimetry using Monte Carlo calculations. Existing MIRD-based mathematical models are easy to compute and standardize, but they are simplified and crude compared to human anatomy. This article describes the development of an image-based whole-body model, called VIP-Man, using transversal color photographic images obtained from the National Library of Medicine's Visible Human Project for Monte Carlo organ dose calculations involving photons, electron, neutrons, and protons. As the first of a series of papers on dose calculations based on VIP-Man, this article provides detailed information about how to construct an image-based model, as well as how to adopt it into well-tested Monte Carlo codes, EGS4, MCNP4B, and MCNPX.
  Health Physics 06/2000; 78(5):476-86. · 1.68 Impact Factor
• Article: A non-destructive method to determine the depth of radionuclides in materials in-situ.

  E P Naessens, X G Xu
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  ABSTRACT: A non-destructive method based on in-situ gamma spectroscopy is developed to determine the depth of radiological contamination in media. An innovative algorithm, Gamma Penetration Depth Unfolding Algorithm (GPDUA), uses point kernel techniques to predict the depth of contamination based on the results of the uncollided peak information from the in-situ gamma spectroscopy. The GPDUA is designed and verified through extensive Monte Carlo simulations and validated through laboratory experiments. This innovative tool promises to be "better, faster, safer, and cheaper" than the current practice in decontamination and decommissioning. The method requires the a priori knowledge of the contaminant source distribution. The applicable radiological contaminants of interest are any isotopes that emit two or more gamma rays per disintegration or isotopes that emit a single gamma ray but have gamma-emitting progeny in secular equilibrium with its parent (e.g., 60Co, 235U, and 137Cs to name a few). The predicted depths from the GPDUA algorithm using Monte Carlo N-Particle Transport Code simulations and laboratory experiments using 60Co have consistently produced predicted depths within 20% of the actual or known depth.
  Health Physics 08/1999; 77(1):76-88. · 1.68 Impact Factor
• Article: Sex-specific tissue weighting factors for effective dose equivalent calculations.

  X G Xu, W D Reece
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  ABSTRACT: The effective dose equivalent was defined in the International Commission on Radiological Protection Publication 26 in 1977 and later adopted by the U.S. Nuclear Regulatory Commission. To calculate organ doses and effective dose equivalent for external exposures using Monte Carlo simulations, sex-specific anthropomorphic phantoms and sex-specific weighting factors are always employed. This paper presents detailed mathematical derivation of a set of sex-specific tissue weighting factors and the conditions which the weighting factors must satisfy. Results of effective dose equivalent calculations using female and male phantoms exposed to monoenergetic photon beams of 0.08, 0.3, and 1.0 MeV are provided and compared with results published by other authors using different sex-specific weighting factors and phantoms. The results indicate that females always receive higher effective dose equivalent than males for the photon energies and geometries considered and that some published data may be wrong due to mistakes in deriving the sex-specific weighting factors.
  Health Physics 02/1996; 70(1):81-6. · 1.68 Impact Factor
• Article: A study of the angular dependence problem in effective dose equivalent assessment.

  X G Xu, W D Reece, J W Poston
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  ABSTRACT: The newly revised American National Standard N13.11 (1993) includes measurements of angular response as part of personnel dosimeter performance testing. However, data on effective dose equivalent (HE), the principle limiting quantity defined in International Commission on Radiological Protection (ICRP) Publication 26 and later adopted by U.S. Nuclear Regulatory Commission (NRC), for radiation incident on the body from off-normal angles are little seen in the literature. The absence of scientific data has led to unnecessarily conservative approaches in radiation protection practices. This paper presents a new set of fluence-to-HE conversion factors as a function of radiation angles and sex for monoenergetic photon beams of 0.08, 0.3, and 1.0 MeV. A Monte Carlo transport code (MCNP) and sex-specific anthropomorphic phantoms were used in this study. Results indicate that Anterior-posterior (AP) exposure produces the highest HE per unit photon fluence in all cases. Posterior-anterior (PA) exposure produces the highest HE among beams incident from the rear half-plane of the body. HE decreases dramatically as one departs from the AP and PA orientations. The results also indicate that overestimations caused by using isotropic dosimeters in assessing effective dose equivalent from near-overhead and near-underfoot exposures are 550%, 390%, and 254% for 0.08, 0.3, and 1.0 MeV, respectively. Comparisons of the angular dependence of HE with those based on the secondary quantities defined in International Commission on Radiation Units and Measurements (ICRU) Reports 39, 43, and 47 show significant differences. This paper discusses why more accurate assessments of HE are necessary and possible. An empirical equation is proposed which can be used as the optimum dosimeter angular response function for radiation angles ranging from 0 degrees to 90 degrees for dosimeter calibration, performance testing, and design.
  Health Physics 03/1995; 68(2):214-24. · 1.68 Impact Factor
• Article: Determining the Effective Dose Equivalent for External Photon Radiation: Calculational Results for Beam and Point Source Geometries

  W D Reece, J.W. Poston Sr, X G Xu
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  ABSTRACT: In 1994, US nuclear plants must implement a new Code of Federal Regulations which adopts the methodology of ICRP 26 for effective dose equivalent (H E ) from internally deposited radionuclides. For exposure to photons from sources outside the body, the new regulations propose an ad hoc extension of the ICRP 26 methodology by defining a new tissue - 'the whole body' - and assigning it a weighting factor of 1. This study provides basic data to build a methodology for assessing H E based on the original ICRP 26 organ dose methods. Specifically, Monte Carlo photon transport calculations were done with anthropomorphic male and female phantoms and a hermaphroditic phantom to calculate organ doses, and thereby H E for each gender, for selected photon energies, for photon beams at any three-dimensional angle, and for point sources anywhere external to the torso. It was found that anterior-posterior beam exposures created the highest H E per unit fluence among all azimuthal and polar beam angles. It was also found that point sources in contact with the gonads yield the highest H E per photon emitted for males and point sources on the sternum yield the highest HE per photon emitted for females.