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J G Wierzbicki

Publications and source records attributed to J G Wierzbicki.

11 recordsLinked to original sources
PubMed1999

Mass attenuation coefficients of clear-Pb for photons from 125I, 103Pd, 99mTc, 192Ir, 137Cs and 60Co.

The mass attenuation coefficients, mu/rho, for Clear-Pb for photon energies ranging from 10 keV to 10 MeV were determined using Monte Carlo methods and simple equations used to manipulate elemental mass attenuation coefficients. It was determined that the effectiveness of Clear-Pb as a radiation shielding material was greater than plain acrylic for all photon energies, especially those less than 150 keV, and for deep penetration problems where the differences in mu/rho between Clear-Pb and acrylic became more significant. Finally, the usefulness of Clear-Pb as a shielding material when compared with acrylic was determined for the following commonly used radionuclides: 125I, 103Pd, 99mTc, 192Ir, 137Cs, and 60Co.

Cesium Radioisotopes↗
PubMed1999

Clinical brachytherapy with neutron emitting 252Cf sources and adherence to AAPM TG-43 dosimetry protocol.

Using Monte Carlo methods, neutron dosimetry for 252Cf Applicator Tube (AT) type medical sources available from Oak Ridge National Laboratory (ORNL) has for the first time been determined in terms of TG-43 formalism. This approach, as compared to previous "along-away" formalisms, demonstrates the relative angular independence of dose rate data, when the geometry factor has been removed. As the ORNL-made 252Cf AT type sources are considerably physically larger than most clinical sources used today, the radial dose function increases for radii less than 3.0 mm due to breakdown of the line source model. A comparison of the 252Cf neutron radial dose function with those for other medical sources revealed similarities with that from 137Cs. Differences with respect to previous 252Cf AT source neutron dosimetry data generally increased at increasing distances. This was attributed to differences in the various 252Cf AT source models and phantom compositions. The current status of 252Cf medical source fabrication and calibration procedures at ORNL is presented.

Anisotropy↗
PubMed1998

Large discrepancies between calculated Dmax and diode readings for small field sizes and small SSDs of 15 MV photon beams.

Clinical observations have revealed that diode readings from 15 MV photon beams with small field sizes and small SSD values were consistently 5%-10% higher than doses calculated at the maximum depth. Dose at depth depends on the collimator scattering factor and the phantom scattering factor--both field size dependent. Diodes are placed on the skin surface, and therefore the phantom scatter factor is different than at depth. In addition, inverse square corrections should be calculated with respect to the location of the diode itself rather than the location of Dmax within the tissue. This may account for about 8% difference between calculated Dmax and diode readings for very small radiation fields and small SSDs, e.g., a prostate boost.

Biophysical Phenomena↗
PubMed1998

Calculated dosimetric parameters of the IoGold 125I source model 3631-A.

Basic dosimetric parameters as recommended by the AAPM Task Group No. 43 (TG-43) have been determined for recently available IoGold 125I brachytherapy seeds. Monte Carlo methods (MCNP) were used in the calculation of these parameters in water, and results compared with soon to be published experimental parameters also for 125I IoGold seeds as well with parameters for model 6702 and 6711 125I seeds. These parameters were the radial dose function, anisotropy factor and constant, and the dose rate constant. Using MCNP, values for the radial dose function at 0.5, 2.0, and 5.0 cm were 1.053, 0.877, and 0.443, respectively. The anisotropy factor was 0.975, 0.946, 0.945, and 0.952 at 0.5, 1.0, 2.0, and 5.0 cm, respectively, with an anisotropy constant of 0.95. The IoGold dose rate constant was determined by excluding the low energy titanium characteristic x rays produced in the IoGold titanium capsule. Using this post TG-43 revised NIST air kerma methodology, the IoGold dose rate constant was 0.96 cGy h-1 U-1. These calculatively determined parameters for IoGold seeds were compared with those determined experimentally for IoGold seeds, and also compared with parameters determined for model 6702 and 6711 seeds as presented in TG-43.

Anisotropy↗
PubMed1997

Modeling of internal dose distributions during SR-89 treatment of a patient with bone metastases.

METHODS: A model of strontium biodistribution similar to the one created by the International Commission on Radiological Protection (ICRP) was applied for activity and absorbed dose calculations in a patient with bone metastases treated with Sr-89 strontium chloride. Metastases are represented just like all other organs and tissues collecting strontium. Data from the ICRP's standard Reference Man were used. RESULTS: Results include calculated time-activity data for all model compartments and for relevant target organs. Absorbed doses per unit administered activity were calculated for blood (0.036 cGy/MBq), soft tissues (0.046 cGy/MBq), bone marrow (1.15 cGy/MBq), bone surface (1.45 cGy/MBq), upper large intestine (ULI) (0.13 cGy/MBq), lower large intestine (LLI) (0.38 cGy/MBq), bladder (0.12 cGy/MBq), and metastases (37.5 cGy/MBq). CONCLUSIONS: Results of the absorbed dose calculations are comparable with results presented in references for specific clinical cases. Discrepancies in dose values may be effected by the size of metastases and the patient's condition.

Bone Neoplasms↗
PubMed1994

Measurement of augmentation of 252Cf implant by 10B and 157Gd neutron capture.

252Cf has been used as a brachytherapy source since the early 1970s. The dominant mechanism of interactions of 252Cf neutrons with tissue is elastic scattering. The scattered neutrons lose part of their energy, which is released as kinetic energy of the recoiling nuclei. By multiple scattering, neutrons lose their energy and eventually become thermalized (in energetic equilibrium with tissue atoms with an average energy of 0.025 eV) and do not play any role in radiotherapy. These thermal neutrons may interact with hydrogen nuclei or with nitrogen, but the cell killing effects by these reaction products are negligibly small compared to the elastic scattering by fast neutrons or by photons emitted by californium. Nonetheless, these thermal neutrons are still potentially usable for neutron capture therapy and can be used to enhance californium brachytherapy effects. Neutron capture therapy is a two-part therapy relying on the selective loading of tumor cells with compounds containing 10B or 157Gd and subsequent irradiation with thermal neutrons. To calculate neutron capture doses one has to know thermal neutron flux. This paper presents results of an experimental study of thermal neutron flux and calculations of boron neutron capture and gadolinium neutron capture doses in the vicinity of 252Cf sources.

Boron Neutron Capture Therapy↗
PubMedDate not supplied

Development of high-activity 252Cf sources for neutron brachytherapy.

The Gershenson Radiation Oncology Center of Wayne State University (WSU), Detroit, Michigan, is using 252Cf medical sources for neutron brachytherapy. These sources are based on a 20-year-old design containing < or = 30 micrograms 252Cf in the form of a cermet wire of Cf2O3 in a palladium matrix. The Radiochemical Engineering Development Center (REDC) of Oak Ridge National Laboratory has been asked to develop very compact, high-activity 252Cf neutron sources for use with remote afterloading equipment in order to reduce treatment times and dose to clinical personnel and to expedite treatment of brain and other tumors. To date, the REDC has demonstrated that 252Cf loadings can be greatly increased in cermet wires and with much smaller diameters. Equipment designed for hot cell fabrication of these wires is being tested. A parallel program is under way to relicense the existing source design for fabrication at the REDC.

Brachytherapy↗