Dosimetry Performance Research Articles

A high-dose dosimeter-based polyvinyl chloride dyed with malachite green

Polyvinyl chloride (PVC) film dyed with malachite green was studied for high-dose radiation dosimetry using visible spectrophotometry. A linear relationship between the relative absorbance and the absorbed dose at the wavelength 628 nm in the range of 0–125 kGy was found. The effect of dose rate, irradiation temperature, film thickness and dye intensity were found not to influence the response. The effects of shelf life and the post-irradiation storage in darkness and indirect daylight conditions on dosimetry performance were discussed.

History of personal dosimetry performance testing in the United States

The basis for personal dosimetry performance testing in the United States is ANSI/HPS N13.11 (2001). Now in its third edition, this standard has been in place since 1983. Testing under this standard is administered by the National Voluntary Accreditation Program (NVLAP), and accreditation of dosimetry processors under this program is required by US Nuclear Regulatory Commission (NRC) regulations. The US Department of Energy (DOE) also maintains a testing program for its laboratories and contractors, administered by the Department of Energy Laboratory Accreditation Program (DOELAP). A focus in recent years has been the modification of ANSI/HPS N13.11 to allow acceptance by both testing programs in order to bring harmonisation to US personal dosemeter processing testing. Since there is no type testing program in the US for personal dosemeters, the testing philosophy of ANSI N13.11 has always combined elements of type testing and routine performance testing. This philosophy is explored in detail in this presentation, along with trends in the development of the document to its present state. In addition, a look will be taken at what the future holds for the next revision of the document, scheduled to begin in 2005.

Optically stimulated luminescence dosimetry performance of natural Brazilian topaz exposed to beta radiation

Optically stimulated luminescence (OSL) has become the technique of choice in many areas of dosimetry. Natural materials like topaz are available in large quantities in Brazil and other countries. They have been studied to investigate the possibility of use its thermoluminescence (TL) properties for dosimetric applications. In this work, we investigate the possibility of utilising the OSL properties of natural Brazilian topaz in dosimetry. Bulk topaz samples were exposed to doses up to 100 Gy of beta radiation and the integrated OSL as a function of the dose showed linear behaviour. The fading occurs in the first 20 min after irradiation but it is <6% of the integrated OSL measured shortly after exposure. We conclude that natural colourless topaz is a very suitable phosphor for OSL dosimetry.

The Third International Intercomparison on EPR Tooth Dosimetry: part 2, final analysis

The objective of the Third International Intercomparison on EPR Tooth Dosimetry was to evaluate laboratories performing tooth enamel dosimetry <300 mGy. Final analysis of results included a correlation analysis between features of laboratory dose reconstruction protocols and dosimetry performance. Applicability of electron paramagnetic resonance (EPR) tooth dosimetry at low dose was shown at two applied dose levels of 79 and 176 mGy. Most (9 of 12) laboratories reported the dose to be within 50 mGy of the delivered dose of 79 mGy, and 10 of 12 laboratories reported the dose to be within 100 mGy of the delivered dose of 176 mGy. At the high-dose tested (704 mGy) agreement within 25% of the delivered dose was found in 10 laboratories. Features of EPR dose reconstruction protocols that affect dosimetry performance were found to be magnetic field modulation amplitude in EPR spectrum recording, EPR signal model in spectrum deconvolution and duration of latency period for tooth enamel samples after preparation.

A miniature, low-cost, user-friendly personal sound-level dosimeter

The objective of this research is to develop a miniature, low-cost, user-friendly personal sound-level dosimeter that can meet the ANSI S1.25-1991 standard. This dosimeter is intended for people whose work-related or recreation-related activities expose them to noises that cause hearing loss. In contrast to typical dosimeters that are controlled by a manager or clinician, the wearer of the miniature dosimeter will also control it and receive its data output to better appreciate his or her sound exposure dose. To significantly miniaturize the dosimeter and lower its cost as compared to typical dosimeters, it will have a reduced feature set, simplified signal processing, an inexpensive microphone capsule, and a microcontroller rather than a digital signal processor. Preliminary tests, using a Texas Instruments embedded controller and an LCD display, suggest that approximations to the standard dosimeter function blocks can be made while maintaining the ANSI tolerances. Tests with inexpensive microphone capsules show acceptable drift due to temperature and humidity for a dosimeter. Following further testing for compliance with the ANSI standard, a limited set of field tests is planned, with wearers using both the miniature dosimeter and a commercial dosimeter, to compare their dosimetry performance.

Gamma-radiation dosimetry with semiconductor CdTe and CdZnTe detectors

Problems related to the dosimetry of γ-radiation, in particular of high intensity, are investigated together with operational performances of detectors, their temperature stability, reproducibility and reliability of detector measurements. A comprehensive study was carried out of CdTe detectors, obtained by the Bridgman growth method, and CdZnTe detectors, crystallized by the Bridgman method at high pressure of inert gas. All the investigated ingots were of p-type conductivity. The current–voltage characteristics and dynamic resistance of detectors from CdTe and CdZnTe were measured over a wide range of operational temperatures (−30 to +70°C) and bias voltages (−300…+300V). The dosimetry performance of CdTe and CdZnTe γ-radiation detectors was tested with standard calibration dosimetry rigs of different intensity. The relation between the detector count rate (count mode of operation) or detector anode current (integrated, or current mode of operation) and the exposure dose rate (EDR) of the γ-radiation was established. The count rate of the radiation registered from different sources (241Am, 137Cs, 60Co) in the count mode depends linearly on EDR in the EDR range from ∼10μR/h up to ∼1R/h. In high-intensity radiation fields a measurement of the current induced by the γ-radiation, i.e. with the detector operating in “current mode”, is preferable. In this case, our researches have shown that the EDR dependence of the output voltage of the current–voltage converter is linear in the range from ∼20R/h up to 5000R/h. Several designs of “detector-absorbing filter” sets were proposed for the correction of the energy dependence of the CdTe and CdZnTe detector absorption efficiency. An experimental detector unit equipped with an optimized “detector-filter” set had a discrete sensitivity of ∼350counts/R (±20%) in the energy range 0.06…1.2MeV.

Ammonium Formate, a Compound for Sensitive EPR Dosimetry

Alanine EPR dosimetry has been applied successfully when measuring intermediate and high radiation doses. Although the performance of alanine dosimetry is being improved, the sensitivity of the material is too low for a fast and simple low- dose determination. Here we present the results using ammonium formate as an EPR dosimeter material. Ammonium formate is seven times more sensitive than alanine, using spectrometer settings optimized for the latter. Deuterated ammonium formate is found to be more than eight times more sensitive than alanine. Analysis of signal stability with time shows that the ammonium formate signal is stable by 5 min after irradiation and that no change in signal intensity is found during 8 days. The atomic composition of ammonium formate is closer to that of tissue than alanine, and thus the energy dependence is smaller than that of alanine at photon energies below 200 keV. Power saturation studies indicate that the energy transfer between the spins and the lattice is fast in ammonium formate, which gives the possibility of using high microwave power without saturation to further increase the sensitivity. These results suggest that ammonium formate has some important properties required of an EPR dosimeter for applications in dosimetry in the dose range typical for radiation therapy.

Characterisation of the ferrous-xylenol orange-gelatin (FXG) gel dosimeter

Recent studies have used the ferrous-xylenol orange-gelatin (FXG) gel dosimeter for 3D radiation field mapping using the optical computed tomography technique. However the characterisation of the dosimetry performance of the FXG gel has not been detailed, such as the variation in dose-response of the FXG gel with changes in preparation techniques, constituent concentrations, pre-irradiation storage time, and concentrations of additives such as oxygen and saccharides. In this paper these issues are addressed with the aim of developing a standard FXG gel for future use in radiation dosimetry applications.

The american brachytherapy society recommendations for permanent prostate brachytherapy postimplant dosimetric analysis

Purpose: The purpose of this report is to establish guidelines for postimplant dosimetric analysis of permanent prostate brachytherapy. Methods: Members of the American Brachytherapy Society (ABS) with expertise in prostate dosimetry evaluation performed a literature review and supplemented with their clinical experience formulated guidelines for performing and analyzing postimplant dosimetry of permanent prostate brachytherapy. Results: The ABS recommends that postimplant dosimetry should be performed on all patients undergoing permanent prostate brachytherapy for optimal patient care. At present, computed tomography (CT) -based dosimetry is recommended, based on availability cost and the ability to image the prostate as well as the seeds. Additional plane radiographs should be obtained to verify the seed count. Until the ideal postoperative interval for CT scanning has been determined, each center should perform dosimetric evaluation of prostate implants at a consistent postoperative interval. This interval should be reported. Isodose displays should be obtained at 50%, 80%, 90%, 100%, 150%, and 200% of the prescription dose and displayed on multiple cross -sectional images of the prostate. A dose -volume histogram (DVH) of the prostate should be performed and the D 90 (dose to 90% of the prostate gland) reported by all centers. Additionally, the D 80, D 100, the fractional V 80, V 90, V 100, V 150, and V 200, (i.e., the percentage of prostate volume receiving 80%, 90%, 100%, 150%, and 200% of the prescribed dose, respectively), the rectal, and urethral doses should be reported and ultimately correlated with clinical outcome in the research environment. On -line real -time dosimetry, the effects of dose heterogeneity, and the effects of tissue heterogeneity need further investigation. Conclusion: It is essential that postimplant dosimetry should be performed on all patients undergoing permanent prostate brachytherapy. Guidelines were established for the performance and analysis of such dosimetry.

LiF:Mg,Cu,P Based Environmental Dosemeter and Dose Calculation Algorithm

The development is described of a new environmental TLD dosemeter badge and dose computation algorithm based on the new LiF:Mg,Cu,P material. LiF:Mg,Cu,P, with its high sensitivity, tissue equivalence, energy independence, and low fading characteristics, is a natural choice for environmental dosimetry. The badge consists of a card and a plastic holder. The card contains four LiF;Mg,Cu,P elements encapsulated in Teflon. The elements are all 3.2 mm square and 0.4 mm thick. The badge is symmetrical and uses four filters to discriminate low and high energy photons and to determine directional dose equivalent, H'(0.07,a), and ambient dose equivalent, H*(10). Extensive data were taken based on irradiations of 920 dosemeters to both single and mixed fields of photons and betas. In addition, angular incidence data of various fields were taken. The approach to the algorithm is empirical and is based on these data. While most algorithms are based solely on perpendicular incidence exposure, this algorithm is being developed to account for the angular response of the dosemeter. The algorithm for perpendicular irradiation is presented. The angular incidence portion of the algorithm is in development. The dosemeter is designed to meet the criteria of the new draft standard ANSI N13.29, 'Environmental Dosimetry Performance - Criteria for Testing'.

Optimized radioiodine therapy of Graves' disease: analysis of the delivered dose and of other possible factors affecting outcome.

The best approach to radioiodine dose selection in the treatment of Graves' hyperthyroidism remains highly controversial. The formula to calculate the individual dose of (131)I to be delivered has been used for half a century and takes into account the thyroid mass, the effective half-life and the maximum uptake of (131)I. The objective of the present study was to evaluate the accuracy of this formula by determining the relationship between the administered dose of (131)I calculated to deliver a target dose of 50Gy to the thyroid and the actual exact organ dose. We further analyzed if therapeutic success, defined by euthyroidism following the individually calculated dose, can be predicted by different pretreatment parameters and particularly by organ dose. One hundred patients with a first episode of Graves' disease and who had received optimal thyroid irradiation after precise dosimetry were retrospectively reviewed. The patients were categorized according to their thyroid function (plasma free thyroxine (T(4)) serum concentration) as eu-, hyper- or hypothyroid during and 1 year after treatment. The relationship between the administered dose and organ dose was assessed by simple regression. We compared free T(4), free tri-iodothyronine, thyroid weight, the number of patients with antithyroperoxidase antibodies and TSH receptor autoantibodies, 24h urinary iodine excretion, (131)I uptake, and the exact dose of (131)I delivered to the thyroid as pretreatment variables. Although we found a correlation between administered dose (mCi) and organ dose (Gy) (r=0.3, P=0.003), the mean coefficient of variation for organ dose was 45%. Individualized radioiodine therapy enabled euthyroidism in 26% of patients and failed in 74% of patients (33% had persistent or recurrent hyperthyroidism and 41% permanent hypothyroidism). (131)I uptake was significantly higher in the hyperthyroidism group in comparison with the euthyroid group. However, organ dose and other pretreatment variables did not differ among the three groups. In conclusion, these results confirm the low performance of individual dosimetry using what are established ratios, since the delivered dose to the gland, although correlated to the intended dose, is highly variable. The finding that other usual pretreatment variables are not different between groups, gives little hope for improving the way of calculating the ideal dose of radioiodine. We suggest to those not yet ready to give a standard or an ablative dose for Graves' hyperthyroidism that they abandon this way to calculate the (131)I dose.

Establishment of ANSI N13.11 X-Ray Radiation Fields for Personal Dosimetry Performance Test by Computation and Experiment

Establishment of ANSI N13.11 X-Ray Radiation Fields for Personal Dosimetry Performance Test by Computation and Experiment

Personal Dosemeter Intercomparisons as Indices of Performance - A Quality Assurance Procedure

This Centre participated in four intercomparisons for personal dosemeters conducted independently by IAEA/RCA, Japan and Australian Radiation Laboratory (ARL), Victoria using CaSO4:Dy Teflon disc-based personal monitoring TLD badges. The irradiations were performed by the organisers free-in-air as well as on the surface of water and PMMA equivalent composite phantoms. The performance of our personal dosemeters in these intercomparisons was analysed using ANSI-N13-11-1983 criteria testing the performance of personal dosimetry. The tolerance level, L, was lower than the limiting value of 0.5 for all the intercomparisons. The results were also analysed using trumpet curve analysis which incorporates the accuracy requirements of ICRP-35 and ICRP-60. The dosemeter quotients (measured dose/conventional true dose) for all irradiated dosemeters fall within the limits of the trumpet curves. These results indicated satisfactory performance of our personal dosemeters in these intercomparisons.

Instrumentation in Thermoluminescence Dosimetry

Abstract In the performance of a thermoluminescence dosimetry (TLD) system the equipment plays an important role. Crucial parameters of instrumentation in TLD are discussed in some detail. A review is given of equipment available on the market today - with some emphasis on automation - which is partly based on information from industry and others involved in research and development.

Instrumentation in Thermoluminescence Dosimetry

In the performance of a thermoluminescence dosimetry (TLD) system the equipment plays an important role. Crucial parameters of instrumentation in TLD are discussed in some detail. A review is given of equipment available on the market today - with some emphasis on automation - which is partly based on information from industry and others involved in research and development.

Choice of Conversion Factors to the Shallow and Deep Dose Equivalents for Use in a U.S. Personnel Dosimetry Performance Testing Programme

In June 1981, the Health Physics Society Standards Committee adopted a standard that will be used in a future mandatory U.S. personnel dosimetry performance testing programme. In this standard, a set of factors is specified for converting from the quantities generally used to characterise the radiation fields in which radiation protection instruments are calibrated to the shallow and the deep dose equivalent specified for reporting the results of future performance tests. For photons, the choice of these conversion factors was the cause of considerable controversy. For this reason, it was decided to publish this relatively detailed discussion of the considerations which were the basis for the choice of all the factors used.