Purpose An interlaboratory comparison of radiation dosimetry was conducted to determine the accuracy of doses being used experimentally for animal exposures within a large multi-institutional research project. The background and approach to this effort are described and discussed in terms of basic findings, problems and solutions. Methods Dosimetry tests were carried out utilizing optically stimulated luminescence (OSL) dosimeters embedded midline into mouse carcasses and thermal luminescence dosimeters (TLD) embedded midline into acrylic phantoms. Results The effort demonstrated that the majority (4/7) of the laboratories was able to deliver sufficiently accurate exposures having maximum dosing errors of ≤ 5%. Comparable rates of ‘dosimetric compliance’ were noted between OSL- and TLD-based tests. Data analysis showed a highly linear relationship between ‘measured’ and ‘target’ doses, with errors falling largely between 0–20%. Outliers were most notable for OSL-based tests, while multiple tests by ‘non-compliant’ laboratories using orthovoltage x-rays contributed heavily to the wide variation in dosing errors. Conclusions For the dosimetrically non-compliant laboratories, the relatively high rates of dosing errors were problematic, potentially compromising the quality of ongoing radiobiological research. This dosimetry effort proved to be instructive in establishing rigorous reviews of basic dosimetry protocols ensuring that dosing errors were minimized.
This report describes the design and initial noise floor measurements of a radiometric calorimeter designed to measure therapeutic medical radioactive sources. The instrument demonstrates a noise floor of approximately 2 nW. This low noise floor is achieved by using high temperature superconducting (HTS) transition edge sensor (TES) thermometers in a temperature-control feedback loop. This feedback loop will be used to provide absolute source calibrations based upon the electrical substitution method. Other unique features of the calorimeter are (a) its ability to change sources for calibration without disrupting the vacuum of the instrument, and (b) the ability to measure the emitted power of a source in addition to the total contained source power.
Solid-state thermocurrent and radioconductivity (electrical conductivity during irradiation) experiments are described with attention to the feasibility of using ionic solids for radiographic imaging. The radioconductivity varies with temperature giving rise to temperature windows of potential usefulness. The electrophotographic image is formed at atmospheric pressure using Al2O3, collecting the charge on mylar film. Development is by the power cloud technique. A transparency, which can be viewed as a conventional radiographic image, is easily produced. A successful transfer image, free of electric discharge artifact, was produced.
Purpose: Photon spectra of a COMET MXR‐320/26 x‐ray tube were measured and corrected for the detector response calculated using Monte Carlo (MC) simulations. Measured (corrected) spectra were compared to spectra from BEAM/FLURZnrc simulations, SpekCalc, and Gesellschaft für Strahlen‐und Umweltforschung mbH München (GSF) Report 560. Methods and Materials: Several NIST‐traceable x‐ray beams ranging from 20 kVp to 250 kVp were measured with a high‐purity germanium detector. The detector was positioned 4.3 m from the focal spot of the tube along the central axis. Pinhole collimation reduced the fluence rates to measurable levels using a tube current of 1 mA.. The entire measurement apparatus was modeled using the MCNP5 MC code. A detector response function was calculated from the model, and the measured spectra were corrected for detector response. The SpekCalc program [Poludniowski et al, Phys. Med. Biol, 54, N433–N438, 2009] was used to generate spectra. The full model of the x‐ray tube was used to simulate spectra with the BEAMnrc and FLURZnrc MC codes. The measured (corrected), calculated and GSF spectra were compared. Results: The measured (corrected) spectra of this investigation generally compare well with those from the BEAMnrc/FLURZnrc simulations, as well as with those generated with the SpekCalc program and from GSF. Differences in the various spectra, particularly in the abundance of W L‐shell fluorescence for the lower energy beams, are largely due to the physics of the programs or codes being used. Conclusions: X‐ray beam measurements using novel correction methods for bremsstrahlung spectra, as well as simulations of the full x‐ray tube geometry, were presented. This direct comparison benchmarks the MC and analytical methods commonly used for x‐ray beam characterization against physical measurements and reveals some of the subtle differences in the various calculation methods.
Purpose: To characterize the component of the LiF:Mg,Ti TLD response to the low‐energy photons of 125normalI and 103Pd LDR brachytherapy sources and x‐ray beam qualities of M40 and M80, that cannot be predicted by cavity theory or Monte Carlo methods. To provide a methodology for determining accurate energy correction factors for experiments performed in a variety of scatter conditions and to provide an example of how to apply the results of this work will also be presented. Method and Materials: TLD‐100 chips were exposed to 125normalI and 103Pd LDR brachytherapy sources using the known geometry of the University of Wisconsin Variable Aperture Free Air Chamber. Dose calculations were based on primary determinations of air‐kerma strength and Monte Carlo simulations of the full irradiation and source geometry. For comparison purposes and to examine the effects of dosimeter size and scatter conditions, a series of x‐ray experiments were performed to compare the response of chips (3×3×0.89mm) to microcubes (1×1×1mm) and free in air irradiations to irradiations in a PMMA holder. Results: The results of the x‐ray experiments agreed well with the work of Nunn et al. (Med. Phys. 2006) and confirmed that the “solid‐state” component of the energy response was largely independent of irradiation geometry. The results of the 125normalI experiments exhibited good reproducibility for the single 125normalI source, but the 103Pd measurements seem to exhibit source‐to‐source variability. More experiments are needed for both isotopes to determine the nature of these observations. Conclusion: For all radiation qualities used in these experiments it was found that Monte Carlo simulations appear to underestimate the dose response of LiF:Mg,Ti when compared to measured response. As a result, the previously published values for the dose rate constants of LDR brachytherapy sources are likely overestimates.
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