Fading characteristics of an alanine-polystyrene dosimeter

Alanine dosimetry is useful for transfer dosimetry by long distance mailing, because of its stability. It has the advantage that the measurement of electron spin resonance (ESR) spectral signal is non-destructive to the dosimeter, with the promise that the method may supply archival dosimetry data, depending on the degree of post-irradiation stability of the signal. The effects of temperature during irradiation and storage on fading of the ESR signal were studied using an alanine dosimeter molded with polystyrene (alanine-PS dosimeter). This investigation covered a long range of storage time (up to 160 days) after irradiation to absorbed doses in the range 1 to 100 kGy, for application to transfer dosimetry between Japan and neighboring Asian countries.Dose response of an alanine-PS dosimeter depends on the temperature during irradiation. The same temperature coefficient of +0.24%/°C was measured at different dose levels of 1, 10 and 100 kGy administered at a constant dose rate of 7 kGy/h. Fading of the dose response was measured under storage at various temperatures (5–40°C). The fading curve generally has two phases with fast and slow fading rates. The response of an alanine dosimeter is relatively stable for doses of 1.4 and 14 kGy, when stored at temperatures below 25°C. However, the degree of fading was roughly 3 and 5% under a storage temperature of 40°C for 5 and 100 days, respectively, after irradiation to 14 kGy. The fading percentages at 100 kGy were 2 and 4% (after 5 days) and 6 and 15% (after 100 days) under the storage temperature of 25 and 40°C, respectively. The fading rates have a relatively small dependence on irradiation temperature. This is observed even when irradiation are made at high temperatures (60°C) and for the doses 100 kGy and above. The mechanism of decay of radicals is discussed to explain the fading characteristics of the two phases of fading. The alanine-PS dosimeter is useful for transfer standard dosimetry up to a dose level of 10 kGy when stored after irradiation at temperature below 40°C. However, consideration of temperature effects during and after irradiation is vital for accurate transfer dosimetry of high doses, especially in the southern Asian countries.     

Responses of alanine dosimeters to irradiations at cryogenic temperatures

Present and future high-energy accelerators and particle detectors use and will use super-conducting technologies where components are submitted to radiation in a cryogenic environment. Radiation tests and dosimetry calibration have to be made under these conditions. Alanine-ESR dosimetry is world-wide recognised as a standard method for high-dose measurements at room-temperature irradiation. From earlier work, the system also seems suitable for low-temperature applications, despite a decrease of sensitivity. The aim of the present work was to estimate the temperature dependence of five different alanine based dosimeters. The dose-response functions at 290, 77 and 5 K were determined between 10 Gy and 80 kGy. All the results were consistent among the five laboratories: at a given dose, the amplitude of the ESR signal decreases with the irradiation temperature, moreover, this effect is found to be dose-dependent.     

Investigation of the influence of calibration practices on cytogenetic laboratory performance for dose estimation

Abstract

Purpose: In the frame of the QA program of RENEB, an inter-laboratory comparison (ILC) of calibration sources used in biological dosimetry was achieved to investigate the influence of calibration practices and protocols on the results of the dose estimation performance as a first step to harmonization and standardization of dosimetry and irradiation practices in the European biological dosimetry network.

Materials and methods: Delivered doses by irradiation facilities used by RENEB partners were determined with EPR/alanine dosimetry system. Dosimeters were irradiated in the same conditions as blood samples. A short survey was also performed to collect the information needed for the data analysis and evaluate the diversity of practices.

Results: For most of partners the deviation of delivered dose from the targeted dose remains below 10%. Deviations larger than 10% were observed for five facilities out of 21. Origins of the largest discrepancies were identified. Correction actions were evaluated as satisfactory. The re-evaluation of some ILC results for the fluorescence in situ hybridization (FISH) and premature chromosome condensation (PCC) assays has been performed leading to an improvement of the overall performances.

Conclusions: This work has shown the importance of dosimetry in radiobiology studies and the needs of harmonization, standardization in irradiation and dosimetry practices and educational training for biologists using ionizing radiation.     

Intercalibration of physical neutron dosimetry for the RA-3 and MURR thermal neutron sources for BNCT small-animal research

New thermal neutron irradiation facilities to perform cell and small-animal irradiations for Boron Neutron Capture Therapy research have been installed at the Missouri University Research Reactor and at the RA-3 research reactor facility in Buenos Aires, Argentina. Recognizing the importance of accurate and reproducible physical beam dosimetry as an essential tool for combination and intercomparisons of preclinical and clinical results from the different facilities, we have conducted an experimental intercalibration of the neutronic performance of the RA-3 and MURR thermal neutron sources.     

In vivo ESR dosimetry in total body irradiation

Total body irradiation (TBI) using high doses (about 10 Gy) with photons in the range between 1 and 10 MV combined with intensive chemotherapy has been used successfully in treatment of acute and chronic leukemia before bone marrow transplantation. One of the principal international guidelines in TBI is to use in vivo dosimetry in order to compare the prescribed dose with that absorbed. The use of in vivo dosimetry is also useful as a retrospective evaluation of any deviation from the prescribed dose greater than +/- 5% for relevant parts of the body, especially in the lung and in other organs at risk. In this paper, Electron Spin Resonance (ESR), using alanine dosimeters, is demonstrated to be a powerful tool for absorbed dose evaluation in TBI by detection of free radicals produced in alanine by ionizing radiation. In this study, we present the results obtained using ESR dosimetry in eleven patients undergoing TBI. The major advantages appear to be: 1. the ESR signal in alanine dosimetry is stable for years without fading: 2. the detection of the ESR signal does not destroy the information and so enables a retrospective judgment of the TBI plan adopted.     

Dose control in the semi-industrial irradiation plant at Ezeiza Atomic Center

High-dose dosimetry is carried out at Ezeiza Atomic Center (CAE) on a routine basis, within the absorbed dose range 10²–10⁵ Gy using potassium nitrate dosimeters (Dorda and Muñoz, 1985). The reference dosimeter is Fricke and Super Fricke. The next inauguration of a private irradiation plant and the increasing interest for a new technology in the industry led us to use a dosimeter easy to be read, without need for wet chemical analysis: the alanine dosimeter (Regulla and Deffner, 1982). Under the influence of ionizing radiation, the alanine in the crystalline state forms stable paramagnetic free radicals. The radical concentration of irradiated alanine, which is proportional to the absorbed dose, can be measured using electron spin resonance (ESR) spectroscopy. The pellets are made of 90% alanine and 10% paraffin. The procedure for mixing is not simple: temperature control is used to get an homogenous mass. The dose evaluation is performed for the ESR signal by measuring the maximum peak-to-peak amplitude. Intercomparison studies were made between the alanine and potassium nitrate dosimeter with good results. The relative standard deviation of our alanine dosimeter at doses of 25 and 32 kGy and 25°C temperature is 4%.     

Intercomparison of the dosimetric system used in industrial irradiation plants in Italy

Industrial applications of ionizing radiation (such as the sterilization of medical supplies, long-lasting food preservation) is a well-established technique all over the world. The efficacy of the treatment depends on accurate dosimetry, which assures both the achievement of irradiation purposes at the lowest cost and the safety of the consumers. This is why in 1986 the Istituto Superiore di Sanità (ISS) started an intercomparison programme among the industrial irradiation plants operating in Italy, aimed at optimizing the applied dosimetric procedures. The electron spin resonance (ESR) alanine-based dosimetry, set up at the ISS, was chosen for reference dosimetry. Each plant received 30 dosimeters to be irradiated in pre-fixed conditions in order to (i) compare the ESR/alanine system and the routine dosimetry; (ii) evaluate the homogeneity factor in the irradiated product; (iii) check the reproducibility of the irradiation technique. Results support the need for standardized dosimetric procedures for an optimization of the radiation treatment.     

The significance of the international dose assurance service for radiation processing

For the standardization of radiation processing dosimetry on an international scale, and for further promotion of dosimetry as quality control measures in high-dose applied research and irradiation industry, the International Dose Assurance Service (IDAS) has been initiated in the framework of the high-dose standardization programme. IDAS is being provided on the basis of an Agreement between IAEA and its Member States. As a transfer standard the GSF-operated ESR/alanine dosimeter has been used for the service. The significance of IDAS and the major achievements made to date are discussed.     

Progress in quality control of alanine dosimeters

The ESR/alanine system has been used for different applications, over several years, as a classical routine dosimetry service. This service is based on alanine dosimeters constituted by pellets manufactured by our laboratory, which are presented with some specifications of use and different parameters bound to the intrinsic quality of the dosimeter itself. These parameters were obtained through the strict application of a production protocol and a validation protocol created, tested and validated under a quality assurance system. Every year, one batch of photon dosimeters is produced and controlled using these protocols and the specifications associated with it are checked. Two categories of data are considered separately: physical parameters and experimental data obtained by measurement on our ESR system are given with their associated standard deviation.     

Reference dosimetry and measurement quality assurance

Measurements of absorbed dose made by a reference dosimetry system, such as alanine, have been suggested for achieving quality assurance through traceability to primary standards. Such traceability can assist users of radiation worldwide in enhancing quality control in medicine, agriculture, and industry. International and national standards of absorbed dose are still needed for applications of γ-ray and electron dosimetry at high doses (e.g. radiation therapy, food irradiation and industrial radiation processing). Reference systems, such as ferrous sulfate dosimeters measured by spectrophotometry and alanine measured by electron spin resonance spectrometry are already well established. Another useful reference system for high doses is supplied as dichromate solutions measured by spectrophotometry. Reference dosimetry, particularly for electron beams, can be accomplished with thin alanine or radiochromic dye film dosimeters.     

Simulation of the neutron flux in the irradiation facility at RA-3 reactor

A facility for the irradiation of a section of patients' explanted liver and lung was constructed at RA-3 reactor, Comisión Nacional de Energía Atómica, Argentina. The facility, located in the thermal column, is characterized by the possibility to insert and extract samples without the need to shutdown the reactor. In order to reach the best levels of security and efficacy of the treatment, it is necessary to perform an accurate dosimetry. The possibility to simulate neutron flux and absorbed dose in the explanted organs, together with the experimental dosimetry, allows setting more precise and effective treatment plans. To this end, a computational model of the entire reactor was set-up, and the simulations were validated with the experimental measurements performed in the facility.     

Measurement of high dose rates by photon activation of indium foils.

Photon activation of indium foils is proposed as a dosimetry technique for high dose rate measurements in a 60Co irradiation facility. The irradiated indium nuclei may be raised to its metastable isomers of 113mIn and 115mIn. The isomer 115mIn, with appreciable induced radioactivity, was selected for dose-rate measurements. Based on the photon flux distribution and the derived dose rates, which were simulated by the MCNP code, the dependence of dose rate measurement sensitivity of indium foils with respect to photon energy at various irradiation distances is described. For practical uses, the radioactivity of 115mIn was linearly related to the dose rate response at the specified irradiation positions. By comparing with a calibrated dosimetry system, the measurement deviation of the indium dosimeter, over dose rates ranging from 10 to 10(4) Gy/h, was evaluated and exhibited an uncertainty of +/- 7%. Other related characteristics including measurement sensitivity and range, linearity with respect to the variation of dose rate, and limitations of the indium dosimeter were evaluated to justify it as an alternative for monitoring dose rate in an irradiation field.     

Analysis of parameters that influence the amplitude of the ESR/alanine signal after irradiation.

When ESR/alanine dosimetry is used for comparison, the time elapsed between irradiation and measurement is critical. Several publications have already mentioned the need for monitoring some of the parameters before, during and after irradiation for accurate normalization of ESR measurements. Nevertheless, neither classification nor coupling effects have yet been mentioned. By application of an experimental design approach, some parameters such as temperature and humidity during storage, before and after irradiation, have been studied. Results are given about the way the signal tends to evolve, ranking the parameters according to their influence and the effects of parameter coupling. A comparison with a conventional approach (study of one parameter at a time) is made. It is proposed to use a normalized ESR measurement that better accounts for the chemical aspect. A better fit of the results (amplitude versus time) is observed when amplitude is corrected taking into account the water content of the dosimeter for a given relative humidity of the surrounding atmosphere during storage.     

Bone marrow dosimetry using blood-based models for radiolabeled antibody therapy: a multiinstitutional comparison.

Standardization of marrow dosimetry is of considerable importance when estimating dose-response for a multicentered clinical trial involving radionuclide therapy. However, it is only within the past five years that the intercomparison of marrow dosimetry results among separate clinical trials that use the same agent has become scientifically feasible. In this work, we have analyzed reported marrow dosimetry results from radioimmunotherapy trials and recalculated marrow absorbed doses at a central facility using a standard blood model with patient-specific source data. The basic approach used in the American Association of Physicists in Medicine (AAPM)/Sgouros marrow dosimetry methodology was common to calculation performed at all participating institutions, including the central facility. Differences in dose estimates associated with starting assumptions and the exact implementation of the AAPM/Sgouros calculation methodology used by the source institutions and the central facility were quantified and compared. METHODS: Data from 22 patients enrolled in radiolabeled antibody clinical trials were randomly selected from 7 participating institutions for the assessment of marrow dose. The analysis was restricted to those patients who were treated with 131I- or 186Re-labeled antibody and had no marrow involvement. Calculation of bone marrow dose at each participating institution was unique to the trial or institution, but all used some form of the AAPM/Sgouros blood model approach. The central facility adopted a marrow dosimetry model based on the AAPM/Sgouros model for radiolabeled antibodies using the standard MIRD approach to the remainder-of-body contribution. A standardized approach to account for variations in patient mass was used for the remainder-of-body component. To simplify clinical implementation, regional marrow uptake and time-dependent changes in the marrow-to-blood concentration ratio were not included. Methods of formatting the collection of standard datasets useful in defining dose-response parameters are also presented. RESULTS: Bone marrow doses were calculated according to the method described for each of the 22 patients based on the patient-specific data supplied by the participating institutions. These values were then individually compared with the marrow doses originally reported by each institution. Comparison of the two calculation methods was expressed as a ratio of the marrow doses for each patient. The mean ratio for the dose estimates at the participating institution calculation compared with the central laboratory value was 0.920 +/- 0.259 (mean +/- SD), with a range from 0.708 to 1.202. CONCLUSION: The independent use of the AAPM/Sgouros method blood model approach to marrow dosimetry has brought these dose estimates to within 30% of the results obtained centrally compared with substantially higher uncertainties reported previously. Variations in calculation methodology or initial assumptions adopted by individual institutions may still contribute significant uncertainty to dose estimates, even when the same data are used as a starting point for the calculation comparison shown here. A clinically relevant, standard method for marrow dosimetry for radiolabeled antibodies is proposed as a benchmark for intercomparison purposes. A parameter sensitivity analysis and a summary discussion of the use of this model for potentially improving dose-response data correlation are also presented.     

A sequential chart for the audit-based evaluation of screening mammogram interpretation

RATIONALE AND OBJECTIVES: Auditing has received much attention recently as a method for radiologists to use to evaluate their interpretation of screening mammograms. U.S. Food and Drug Administration regulations require that some sort of audit be in place before a mammography screening facility can receive accreditation. Auditing presents a unique opportunity to monitor accuracy continually and identify problems early. Audit data present unique challenges, however, and appropriate methods must be used to control the risk of errors. MATERIALS AND METHODS: This article introduces a simple method for the task of deciding if a radiologist yields an acceptable positive predictive value based on audit. The method is based on "sequential" decision-making techniques that have found wide application in quality control problems. These techniques are developed for diagnostic radiology and embodied in an easy-to-use decision-making chart. RESULTS: Several examples, based on audit data from actual mammography facilities, provide insights into the use of these charts and the influence of (a) the selection of standards, (b) the selection of error risks, and (c) radiologist variability. The examples also serve to demonstrate another important property of this method--that is, it specifies the minimum amount of data that has to be collected before any decision can reliably be made. CONCLUSION: The chart presented in this article provides a method by which audit data can be used objectively to evaluate the accuracy of screening mammogram interpretation. The method controls the risk of either falsely accepting an unqualified radiologist or falsely rejecting a qualified radiologist. It should be a useful tool to radiologists who must evaluate their own practices.     

An automated system for the measurement of alanine/EPR dosimeters

NPL for several years has offered mailed reference dosimetry services based on alanine/EPR dosimeters, both at industrial and therapy dose levels. Compared to other methods of reference dosimetry, operator involvement in alanine/EPR has been found to be relatively high, and contributes significantly to the overall economics of the process. Commercially available sample changers are not suitable for high accuracy applications, and it has proved necessary to develop a dedicated automation system to handle NPL alanine dosimeter pellets. In this paper we describe an automatic sample changer for placing and retrieving alanine pellets into and out of the cavity of a standard research grade EPR spectrometer. Up to 32 pellets can be held in each removable sample tray. The sample changer software has been interfaced into the spectrometer control software to enable complete automation of the measurement process, including the optimization of spectrometer settings and rotation of the sample within the cavity.     

Alanine dosimetry as the reference dosimetric system in accelerator radiation environments

The estimation of the lifetime of components in high-radiation environments is of great importance in high-energy particle accelerators. Therefore, the measurements of absorbed dose around primary-beam areas is carried out at CERN to give information on radiation damage and preventive maintenance of materials. In the framework of a collaboration between CERN and the Istituto Superiore di Sanitá (ISS), the following high-dose dosimeter types were compared using ISS alanine dosimetry as the reference system; radio-photoluminescence glass (RPL), polyethylene hydrogen pressure, phosphate glass, LiF crystals and colour indicators. All of them were calibrated against alanine in controlled conditions with ⁶⁰Co y-rays in the range 1–10⁵Gy at ISS; a calibration between 10⁵ and 10⁶ Gy was performed at an industrial radiation facility, using calculated dose values as reference. Specimens of each dosimetric system were then exposed at the main CERN proton accelerators and at the electron accelerator at DESY (F.R.G.). Results suggest that the most suitable dosimetric systems for use in the radiation field of high-energy particle accelerators are RPL, hydrogen pressure and alanine. Some preference should be given to alanine, because of the wide dose range covered, the low-energy dependence, the low fading and the small size.     

High-level gamma dosimetry using phototransferred thermoluminescence in quartz

Phototransferred thermoluminescence (PTTL) in natural quartz, separated from sand, has been studied for its application in high-level gamma dosimetry. The paper reports dose-vs.-PTTL response of 110°C and 180°C peaks in the dose range of 10 Gy to 6 kGy. Using this method, the dose rate delivered to the sewage sludge during irradiation at SHRI facility, Vadodara, India, was estimated to be 0.35±0.02 kGy/h.     

Ammonium tartrate as an ESR dosimeter material

This study is one step in the search for an ESR dosimeter material with a higher signal intensity than the commonly used l-α-alanine, to be useful in the clinical dose range (approximately 0.1–20 Gy). The substance ammonium tartrate was found and investigated regarding signal intensity, radical stability, dose response and dose resolution. The ESR signal intensity of ammonium tartrate was shown to be more than twice the intensity of the alanine signal. The data indicate that an unstable radiation induced radical contributes to the ESR signal initially; after a couple of hours it has converted to a secondary radical which has a decay slow enough to be considered stable during the first two weeks after irradiation. Ammonium tartrate has a linear dose response in the investigated range of 0.5–4000 Gy and a dose resolution of 0.1 Gy at the 0.5 Gy level where, as a comparison, the corresponding value for alanine is 0.3 Gy. We thus find the substance suitable for clinical dosimetry.     

牙釉质EPR剂量测定方法的主要影响因素分析

EPR(电子顺磁共振)剂量测定方法是回顾性测定个人辐射剂量的主要方法,它能够准确估算出很久以前发生的辐射照射事件的吸收剂量值,其理论基础是在牙釉质中,辐射所致自由基水平随着辐射剂量的增加而增加。目前,将EPR方法用于低剂量测定还存在一些困难,为了降低测量阈值,减小误差,优化方法,需要进一步研究该方法的影响因素。本文重点分析了影响牙釉质EPR剂量方法测量阈值和测量结果不确定度的主要因素,并对解决这些问题的修正方法进行了讨论。