Biomedical subjects

Gary H Kramer

Publications and source records attributed to Gary H Kramer.

At least 19 recordsLinked to original sources

PubMed2007

The standfast whole body counter and the sliced BOMAB phantom: efficiency as a function of number of sources and energy modeled by MCNP5.

Previously, using Monte Carlo simulations, this laboratory conceptualized a new phantom: the sliced Bottle Manikin Absorber (BOMAB) phantom. It was intended for calibration or performance testing of whole body counters and the HML subsequently built and tested that phantom. Also, this laboratory tested another phantom used for the calibration of the StandFast whole body counter and identified some deficiencies. This paper investigates the use of the sliced BOMAB phantom as an alternative for the calibration of the StandFast and shows how the 165 sources required for a full loading of the sliced BOMAB can be reduced to a much smaller number without compromising the calibration. The agreement of the sliced BOMAB with eight sources is approximately 1% when compared with a conventional BOMAB phantom.

Body Burden↗

PubMed2007

Evaluation of two commercially available portal monitors for emergency response.

The Human Monitoring Laboratory has compared two types (the P3 and the MiniSentry) of portal monitors that can be field deployed in response to an emergency. They can be used to screen persons for internal or external radioactive contamination by fission activation products (neither unit is capable of detecting alpha or beta radiation, and the amount of material required to alarm the monitors is unacceptably high for low energy x rays or gamma rays) following an incident involving the release of radioactive material (accidental or intentional). It was found that the P3 benefits from simplicity but requires slightly more activity to alarm than the MiniSentry, although for emergency response, the amount of activity that can be detected is far below a level where significant health effects will occur. The MiniSentry was found to have more capability than the P3, but these benefits also bring their own disadvantages. It was also found that the MiniSentry would be difficult to deploy in an outdoor setting whereas the P3 is well designed for a field setting. Despite the differences found, the HML has concluded that both have a distinct place in emergency monitoring. In the future, the HML plans to have both instruments ready for field deployment.

Disaster Planning↗

PubMed2006

Large area germanium detector arrays for lung counting: what is the optimum number of detectors?

Using the Lawrence Livermore National Laboratory (LLNL) torso phantom to calibrate a lung counting system can lead to the conclusion that three large area (i.e. >70 mm diameter) Ge detectors will outperform a four-detector array and provide a lower MDA as a four-detector array of large area Ge detectors covers a significant portion of inactive tissue (i.e. non-lung tissue). The lungs of the LLNL phantom, which are approximately 10 cm too short compared with real lungs, also suggests that a two-detector array could be used under limited circumstances. When tested with modified lungs that are more human-like, it was found that the four-detector array showed the best counting efficiency and the lowest MDA. Fortunately, these findings indicate that, although the LLNL phantom's lungs are too short, there is no adverse impact on the calibration of a lung counter.

Computer Simulation↗

PubMed2006

The sliced bomab phantom: a new variant for intercomparison.

Previously, this laboratory conceptualized a new phantom for calibration or performance testing of whole body counters using Monte Carlo simulations. This paper describes the physical reality that was created from the Monte Carlo design project and compares its counting efficiency to that of a conventional BOMAB phantom using two whole body counters. In one counter (NaI based) the agreement between the two phantoms was +/-8% and in the second counter (Ge based) the agreement was +/-5% at all the energies measured (126 keV, 661 keV, 1172 keV, 1330 keV). The advantage of the sliced phantom is that the sources are solid, sealed, and cannot leak activity thereby simplifying packing for shipment if the phantom is classified as a Dangerous Good. The new phantom is, therefore, ideal for uses that involve shipment, such as an intercomparison exercise. The phantom is also re-usable as the sources can be changed.

Female↗

PubMed2006

A commentary on some inconsistencies in the icrp 2005 recommendations: exclusion levels.

The International Commission on Radiological Protection (ICRP) 2005 Recommendations, which were released at the International Radiation Protection Association's congress held in Madrid (May 2004), have been available for public comment via the ICRP's Web site. The comment period has now closed and the Recommendations are presumably being re-worked. There are several inconsistencies in the Recommendations and they are exemplified by looking at the exclusion levels in more detail. The relevant text of the Recommendations is included in this paper as an . It is suggested that the International Atomic Energy Agency's approach is more balanced where each nuclide receives its own exclusion level instead of the incomplete and arbitrary categories proposed by the ICRP.

Health Physics↗

PubMed2006

Sensitivity of portable personnel portal monitors: potential problems when dealing with contaminated persons.

Health physicists are usually concerned with small amounts of radioactivity and strive to develop techniques to measure them; however, following a terrorist attack involving radioactive materials the converse might be the case, and exposed persons may be heavily contaminated. The Human Monitoring Laboratory (HML) has field tested its Portable Personnel Portal (P3) monitors using sources up to 1,700 MBq (47 mCi) to determine the alarm distance as a function of activity. The results show that the P3 monitors are highly sensitive, so much so that siting will be a problem for multiple units if multiple alarms are to be avoided. Building materials will shield the monitors allowing units to be placed closer together than in the open where there is no shielding, but windows and doors reduce shielding and complicate the siting of multiple units. In either situation, careful prior thought should be given to siting the monitors and the logistics of crowd control techniques.

Artifacts↗

PubMed2005

Evaluation of the new graded Z liner in the Human Monitoring Laboratory's lung counter.

The Human Monitoring Laboratory has recently completed the graded Z shielding in its lung counting chamber. The addition of a layer of tin and a layer of copper over the existing layer of lead that lined the thick steel walls has improved the background, as confirmed by long counts before and after the shielding was added. The graded Z liner was successful in reducing the general background in the lower energy regions by an average of 16% over the eight regions studied in the range 15-200 keV, over previous values.

Artifacts↗

PubMed2005

A new phantom for use in whole body counters: a Monte Carlo design project.

A new phantom for calibration or performance testing of whole body counters has been conceptualized. The validity of the design has been validated by Monte Carlo simulations. The simulations have compared the expected counting efficiencies for the new design to those of a conventional phantom; both phantoms were placed in a virtual copy of the Human Monitoring Laboratory's whole body counter. The simulations covered a wide energy range (126-2,754 keV), and the agreement between the two types of phantoms was 0.988 +/- 0.005. Based on these findings, a prototype sliced BOMAB phantom corresponding to a Reference Female will be constructed. If the results were unfavorable, as was not the case, then the expense of building and testing the phantom would have been avoided.

Female↗

PubMed2005

The W-chair whole body counter: a Monte Carlo investigation.

The W-chair whole body counting geometry, a derivative of the meter-arc counting geometry, has been examined using Monte Carlo simulations to investigate the effect of phantom size on the counting efficiency. Three detector positions were simulated (42 cm, 71 cm, and 100 cm from the chair), with one being very close to the physical counting geometry in use at the Whiteshell Laboratories, to investigate the effects of detector-chair distance. The agreement of the simulations with observed counting efficiencies was within 7% over the energy region of 122 keV to 1,173 keV. The optimum counting geometry was found to be the 71-cm detector-chair distance as this balances both sensitivity and counting efficiency. The range of relative counting efficiencies is 0.94 to 1.13 for all energies studied (126 keV to 2,754 keV) and selected phantom sizes relative to the Reference Man phantom. This range also represents the extent of the activity estimate's uncertainty if no size correction factors are applied during routine counting and shows the W-chair counting geometry to be relatively subject-size independent.

Algorithms↗

PubMed2005

Performance characteristics of a commercially available whole body counting phantom measured experimentally and using Monte Carlo simulations.

The performance characteristics of a commercially available whole body counting phantom have been examined experimentally and using Monte Carlo simulations. The counting efficiency as a function of photon energy (126 keV to 2,754 keV) obtained using this phantom has been compared with those obtained using a real or virtual BOMAB phantom in a scanning detector and a FastScan whole body counter. The results suggest that the commercially available whole body counting phantom is equivalent to a BOMAB phantom under certain circumstances but that under other measurement conditions it may be necessary to develop correction factors.

Algorithms↗

PubMed2005

Effect of lung volume on counting efficiency: a Monte Carlo investigation.

Lung counters are usually calibrated with an anthropometric phantom that has a fixed lung size; however, people have widely varying lung sizes (both volume and dimensions). This work uses a simple Monte Carlo simulation to investigate the effect on the counting efficiency of a lung counter based on a four detector array of 50 mm diameter, 70 mm diameter, or 85 mm diameter as lung size varies. The simulations were carried out at several photon energies (17, 60, 120, and 1,000 keV). Comparing the simulated efficiencies with a reference value close to the lung volume of Reference Man, biases in the range of -21% to 63% were discovered. The values from the Monte Carlo simulation have also been compared with some literature data based on experimental measurements, and the agreement was found to be comparable suggesting that lung volume is indeed a factor that should be considered when trying to make an accurate estimate of a lung burden.

Algorithms↗

PubMed2005

The Human Monitoring Laboratory's new lung counter: calibration and comparison with the previous system and the Cameco Corporation's lung counter.

The Human Monitoring Laboratory has replaced its lung counting system with four large area (85 mm x 30 mm) HPGe detectors, electronics, and software. The system has been calibrated with the same lung set and phantom that was used to calibrate the Human Monitoring Laboratory's previous lung counting system and the Cameco Corporation's mobile lung counter. The performance characteristics (efficiency and sensitivity) of all three systems are compared, with the Human Monitoring Laboratory's new system being more sensitive than the other systems by factor of 1.3. The large area detectors highlight the design deficiency of the Lawrence Livermore National Laboratory's torso phantom, namely short lungs, as the lower two detectors are over inactive tissue (approximately 40%). As a result, both a two-detector and a three-detector array are actually more sensitive than a four-detector array in certain circumstances. This is, however, an unrealistic finding as human lungs are much longer (approximately 10 cm) than the Lawrence Livermore National Laboratory's phantom's lungs. The dosimetric implications of the new system's minimum detectable activities are put into perspective using (57)Co, (235)U, (238)U, (239)Pu, (241)Am, and natural uranium as example radionuclides.

Air Pollutants, Radioactive↗

PubMed2005

The HML's new field deployable, high-resolution whole body counter.

The Human Monitoring Laboratory has found an alternate use for a hyperpure germanium field deployable instrument that was originally designed to be used in a search and identify mode for contraband radioactive material. The instrument, the Ortec Detective, becomes a fully functional spectroscopy system when connected to a laptop computer. In this configuration it can be used as a high-resolution portable whole body counter. This work has determined that the instrument has adequate sensitivity for emergency response with respect to fission and activation products, but not actinides. The use of Monte Carlo simulations has allowed the HML to calibrate the instrument, partially optimize the counting geometry, and develop a calibration curve that is a function of photon energy and a person's size. Similarly for thyroid counting, a function has been found that fits counting efficiency to a person's height. The MDA's are a few kilo Becquerels for fission and activation products for a 5-min count in an unshielded environment using a male subject.

Calibration↗

PubMed2004

Summing coincidence errors using 152Eu lungs to calibrate a lung-counting system: are they significant?

The use of a lung phantom containing 152Eu/241 Am activity can provide a sufficient number of energy lines to generate an efficiency calibration for the in vivo measurements of radioactive materials in the lungs. However, due to the number of energy lines associated with 152Eu, coincidence summing occurs and can present a problem when using such a phantom for calibrating lung-counting systems. A Summing Peak Effect Study was conducted at three laboratories to determine the effect of using an efficiency calibration based on a 152Eu/241 Am lung phantom. The measurement data at all three laboratories showed the presence of sum peaks. While one of the laboratories found only small biases (< 5%) when using the 152Eu/241 Am calibration, the other facilities noted up to 30% positive bias in the 140 keV to 190 keV energy range that prevents the use of the 152Eu/241 Am lung phantom for routine calibrations. Although manufactured by different vendors, the three facilities use similar types of germanium detectors (38 cm2 by 25 mm thick or 38 cm2 by 30 mm thick) for counting. These results underscore the need to evaluate the coincidence summing effect, which appear system dependent, when using a nuclide such as 152Eu for the calibration of low-energy lung counting systems and highlight the problem of using a general calibration curve in place of specific nuclide calibration factors.

Artifacts↗

PubMed2004

The use of autoradiography for investigating the distribution of radioactivity in lung counter calibration sources.

This paper shows that autoradiography is a useful technique for investigating radioactivity distributions in lung phantoms and planar sources. It was applied to a sliced lung phantom that had activity homogeneously distributed throughout the tissue substitute material and to laminated planar sources in an attempt to answer three questions: 1) Was the activity distribution the same in each slice of the sliced homogeneous lung set? 2) Was the activity distribution the same for each of the laminated planar sources? and 3) Were the activity distributions the same between slices and planar sources? The activity distribution, including identification of some locations of elevated activity in the sliced homogeneous lungs, was easily obtained using autoradiography. This study demonstrates that neither the sliced homogeneous lung sets nor the laminated planar sources had a homogeneous distribution of radioactivity, as had been previously thought.

Autoradiography↗

PubMed2003

Comparison of sliced lungs with whole lung sets for a torso phantom measured with Ge detectors using Monte Carlo simulations (MCNP).

Lung counters are generally used to measure low energy photons (<100 keV). They are usually calibrated with lung sets that are manufactured from a lung tissue substitute material that contains homogeneously distributed activity; however, it is difficult to verify either the activity in the phantom or the homogeneity of the activity distribution without destructive testing. Lung sets can have activities that are as much as 25% different from the expected value. An alternative method to using whole lungs to calibrate a lung counter is to use a sliced lung with planar inserts. Experimental work has already indicated that this alternative method of calibration can be a satisfactory substitute. This work has extended the experimental study by the use of Monte Carlo simulation to validate that sliced and whole lungs are equivalent. It also has determined the optimum slice thicknesses that separate the planar sources in the sliced lung. Slice thicknesses have been investigated in the range of 0.5 cm to 9.0 cm and at photon energies from 17 keV to 1,000 keV. Results have shown that there is little difference between sliced and whole lungs at low energies providing that the slice thickness is 2.0 cm or less. As the photon energy rises the slice thickness can increase substantially with no degradation on equivalence.

Calibration↗

PubMed2003

Lung counting: summing techniques to reduce the MDA.

The new dose limits recently adopted in Canada (and elsewhere in the world) have made it more difficult to detect some radionuclides by in vivo counting at the average dose limit of 20 mSv. This is particularly true for natural uranium. Two techniques have been developed by the Human Monitoring Laboratory to reduce the Minimum Detectable Activity (MDA) for the lung counting of this nuclide. The first technique, developed in collaboration with Cameco, is to either sum sequential counts of an individual or to sum spectra of a group of workers similarly occupationally exposed. This technique offers a reduction in the MDA of up to a factor of three. The second technique, developed in collaboration with CNEN, involves the summing of photopeaks within an individual spectrum and offers a reduction in the MDA of up to a factor of two.

Adult↗

PubMed2003

Problems encountered during the calibration of the new Cameco mobile lung counter: detector size or phantom limitation?

This paper describes the calibration of the new Cameco mobile lung counter and, more importantly, the problems encountered with recommendations for their long-term solution. The new Cameco lung counting system, which is based on an array of four 80-mm-diameter Canberra BeGe detectors, has used the JAERI phantom for its primary calibration as it more closely resembles ICRP reference data for lung dimensions compared with the LLNL phantom. Although the JAERI phantom's lung dimensions offer advantages over the LLNL phantom's lungs, this phantom is still not ideal. The work described in this paper leads to the conclusion that the LLNL be modified to more closely resemble the ICRP reference data if large area germanium detectors comprise the lung counter. Overlay plate stacking was necessary to achieve the range of chest wall thicknesses found within the Cameco work force (2-8 cm) when using the JAERI phantom. This technique has proved to be robust and is useful for extending the calibration range. Cameco is using group monitoring, which adds spectra to simulate very long counting times (10-20 h), and it is essential that all materials be low background. This was not initially the case here as found from overnight background counts.

Air Pollutants, Radioactive↗