Contribution of ESR dosimetry for irradiation of geological and archaeological samples with a Co panoramic source

A very precise dosimetry of a field of artificial irradiation is essential to estimate an accurate ESR Equivalent Dose (ED) in archaeology and geology. Archaeological powder samples and one sample of DL-alanine powder as control were prepared by IPH. Some alanine dosimeters of LMRI, constituted of L-alanine pellets, were joined to the IPH samples and together, irradiated in boxes using panoramic ⁶⁰Co source under different experimental conditions. The LMRI had in charge the control of the process of irradiation and the measurement of each absorbed dose and dose rate delivered to the different series of boxes. This study consists in the evaluation of the distribution of dose on the samples. The ESR measurements made by the two laboratories were analysed and then compared. These experiments showed a significant gradient in the absorbed dose delivered to each LMRI dosimeter. The dispersion in each box was easily observable. However, a good agreement between the dosimeters and the alanine powder was observed in a same box.     

Acidic aqueous dichromate solutions as reference dosimeters in the 10–40 kGy range

The radiolytic reduction of dichromate ion in acidic aqueous solution has been investigated as a potential dosimetry system for the 10–40 kGy range of absorbed dose. Dilute sulphuric acid has been shown to be unsuitable as a solvent, and the use of 0.1 mol·dm⁻³ perchloric acid is recommended. A previously reported effect of silver ion in supressing reaction with hydrogen has been confirmed, and in addition, silver ions have been shown to be effective in eliminating dose rate effects. The temperature coefficient during irradiation has been determined as −0.2% per degree and post-irradiation storage effects are shown to be negligible. The precision of the system is about 0.5% at a dose of 25 kGy, and a suggested composition for a working dosimeter is given.     

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%.     

Radiochromic solutions for reference dosimetry

A chemical radiochromic dosimeter using hexa(hydroxyethyl)pararosaniline nitrile (HHEV-CN) dissolved in an aerated mixture of triethyl phosphate and dimethyl sulfoxide can be used over a wide absorbed dose range as a stable reference dosimeter, with useful characteristics, both for steady-state and pulsed radiation fields. Solutions of the leuco dye at 2-mM concentration, containing small amounts of acetic acid, p-nitrobenzoic acid and polyvinylbutyral, show high precision and a linear response for absorbed doses up to 4 kGy. When the leuco dye concentration is increased to 100 mM, the response is also linear, and absorbed doses as low as 0.5 Gy can be read with a precision of 1.3% (95% confidence limits). The radiation chemical yield is constant with changes in absorbed dose rate, but it increases with concentration of the leuco dye up to 10⁻¹ molarity. The radiation chemical yields for dye formation are: for 2-mM solution, G(dye) = 0.015 μmol J⁻¹; for 100-mM solution, G(dye) = 0.28 μmol J⁻¹. The uncertainties for these measured values are ±2.6% (95% confidence limits). The molar linear absorption coefficient at 605–608 nm wavelength is 1.0 × 10⁵ L mol⁻¹ cm⁻¹, the uncertainty (95% confidence limits) being ±2.2%. This dosimeter solution may be used in small sealed glass ampoules or plastic vials and is useful for measuring x- and γ-ray doses of interest in food irradiation and in clinical radiology. The combination of ingredients simulates water and biological tissue (muscle) in terms of radiation interaction cross sections, i.e. mass energy-absorption coefficients for photons (0.1–20 MeV) and mass collision stopping powers for electrons (0.1–50 MeV).     

A polymer-alanine film for measurements of radiation dose distributions

A film dosimeter (0.35 mm thick) composed of polyethylene-vinyl acetate and microcrystalline l-α-alanine has been prepared and investigated with respect to dosimetric properties using electron spin resonance spectroscopy. The useful absorbed dose range is ∼ 25 to 10⁵ Gy and no dose-rate dependence of the response is observed between 1 and 10⁷ Gy s⁻¹ within the dose range up to 50 kGy. With irradiation temperature increasing from 25 to 80°C, the response increases at most by 10%. The response is stable, within experimental uncertainty, at least up to 2500 h after irradiation. The suitability of the polymer-alanine film for measurements of ionizing photon and electron dose distributions is demonstrated.     

Feasibility study of radiophotoluminescent glass rod dosimeter postal dose intercomparison for high energy photon beam

A radiophotoluminescent glass rod dosimeter (GRD) system has recently become commercially available. In this study we evaluated whether the GRD would be suitable for external dosimetric audit program in radiotherapy. For this purpose, we introduced a methodology of the absorbed dose determination with the GRD by establishing calibration coefficient and various correction factors (non-linearity dose response, fading, energy dependence and angular dependence). A feasibility test of the GRD postal dose intercomparison was also performed for eight high photon beams by considering four radiotherapy centers in Korea. In the accuracy evaluation of the GRD dosimetry established in this study, we obtained within 1.5% agreements with the ionization chamber dosimetry for the ⁶⁰Co beam. It was also observed that, in the feasibility study, all the relative deviations were smaller than 3%. Based on these results, we believe that the new GRD system has considerable potential to be used for a postal dose audit program.     

Comparison of 3D dose distributions for HDR 192Ir brachytherapy sources with normoxic polymer gel dosimetry and treatment planning system

Radiation fluence changes caused by the dosimeter itself and poor spatial resolution may lead to lack of 3-dimensional (3D) information depending on the features of the dosimeter and quality assurance of dose distributions for high–dose rate (HDR) iridium-192 (¹⁹²Ir) brachytherapy sources is challenging and experimental dosimetry methods used for brachytherapy sources are limited. In this study, we investigated 3D dose distributions of ¹⁹²Ir brachytherapy sources for irradiation with single and multiple dwell positions using a normoxic gel dosimeter and compared them with treatment planning system (TPS) calculations. For dose calibration purposes, 100-mL gel-containing vials were irradiated at predefined doses and then scanned in an magnetic resonance (MR) imaging unit. Gel phantoms prepared in 2 spherical glasses were irradiated with ¹⁹²Ir for the calculated dwell positions, and MR scans of the phantoms were obtained. The images were analyzed with MATLAB software. Dose distributions and profiles derived with 1-mm resolution were compared with TPS calculations. Linearity was observed between the delivered dose and the reciprocal of the T2 relaxation time constant of the gel. The x-, y-, and z-axes were defined as the sagittal, coronal, and axial planes, respectively, the sagittal and axial planes were defined parallel to the long axis of the source while the coronal plane was defined horizontally to the long axis of the source. The differences between measured and calculated profile widths of 3-cm source length and point source for 70%, 50%, and 30% isodose lines were evaluated at 3 dose levels using 18 profiles of comparison. The calculations for 3-cm source length revealed a difference of > 3 mm in 1 coordinate at 50% profile width on the sagittal plane and 3 coordinates at 70% profile width and 2 coordinates at 50% and 30% profile widths on the axial plane. Calculations on the coronal plane for 3-cm source length showed > 3-mm difference in 1 coordinate at 50% and 70% and 2 coordinates at 30% profile widths. The point source measurements and calculations for 50% profile widths revealed a difference > 3 mm in 1 coordinate on the sagittal plane and 2 coordinates on the axial plane. The doses of 3 coordinates on the sagittal plane and 4 coordinates on the axial plane could not be evaluated in 30% profile width because of low doses. There was good agreement between the gel dosimetry and TPS results. Gel dosimetry provides dose distributions in all 3 planes at the same time, which enables us to define the dose distributions in any plane with high resolution. It can be used to obtain 3D dose distributions for HDR ¹⁹²Ir brachytherapy sources and 3D dose verification of TPS.     

手表红宝石事故剂量计在电离辐射事故剂量测量中的应用

研制了两种用于手表红宝石事故剂理计测量的特殊热释光剂量读出装置；对国内、外１０种不同种类、型号的手表红宝石热释光剂理特性进行了实验研究，结果表明：在热释发光曲线、灵敏度、重复使用性、衰退性、光敏性、能量响应、剂量响应等性能满足事故个人剂量测量的要求，手表红宝石是目前人体佩戴物中方便易得的实用个人事故剂量计；在几起辐射事故中得到了成功的应用，其中列举了一起有代表性的＾６０Ｃｏ源事故受照者的剂量测量和     

ESR dosimetry of a deceased radiation worker

A case of overexposure of an industrial radiographer using ¹⁹²Ir sources and having a filmbadge dosimeter record of 104 mSv has been examined with ESR dosimetry of postmortem tooth and bone specimens. ESR measurements of the tooth enamel showed an intense signal of CO₂⁻ and gave the equivalent dose (ED) of 14 Gy by the additive dose method using γ-rays from a source of ⁶⁰Co. The doses for a finger bone and humerus were 14.7 and 7.0 Gy, respectively. It was concluded that he had been exposed to radiation repeatedly over 10 yr and that ESR dosimetry can give a life-long cumulative dose for personnel using radiation.     

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.     

Alanine-ESR In Vivo dosimetry: a feasibility study and possible applications

A new alanine-ESR dosimeter has been developed at AERIAL in order to study its potential use in radiotherapy. Alanine-ESR results are compared with ion chamber for depth-dose measurements. A good concordance has been found between provisional dosimetry and absorbed dose during high dose rate and intra operative treatments. The results of the experiments indicate that alanine-ESR dosimetry is suited to check dose optimisation routines and seems to be a promising in vivo dosimetry technique.     

Time-resolved in vivo dosimetry for source tracking in brachytherapy

PurposeThe purpose of this article is to demonstrate that brachytherapy source tracking can be realized with in vivo dosimetry. This concept could enable real-time treatment monitoring.MethodsIn vivo dosimetry was incorporated in the clinical routine during high-dose-rate prostate brachytherapy at Aarhus University Hospital. The dosimetry was performed with a radioluminescent crystal positioned in a dedicated brachytherapy needle in the prostate. The dose rate was recorded every 50–100 ms during treatment and analyzed retrospectively. The measured total delivered dose and dose rates for each dwell position with dwell times >0.7 s were compared with expected values. Furthermore, the distance between the source and dosimeter, which was derived from the measured dose rates, was compared with expected values. The measured dose rate pattern in each needle was used to determine the most likely position of the needle relative to the dosimeter.ResultsIn total, 305 needles and 3239 dwell positions were analyzed based on 20 treatments. The measured total doses differed from the expected values by −4.7 ± 8.4% (1SD) with range (−17% to 12%). It was possible to determine needle shifts for 304 out of 305 needles. The mean radial needle shift between imaging and treatment was 0.2 ± 1.1 mm (1SD), and the mean longitudinal shift was 0.3 ± 2.0 mm (1SD).ConclusionTime-resolved in vivo dosimetry can be used to provide geometric information about the treatment progression of afterloading brachytherapy. This information may provide a clear indication of errors and uncertainties during a treatment and, therefore, enables real-time treatment monitoring.     

Patient-specific dosimetry for intracavitary 32P-chromic phosphate colloid therapy of cystic brain tumours

Purpose

³²P-chromic phosphate colloid treatments of astrocytoma and craniopharyngioma cystic brain tumours in paediatric patients are conventionally based on a sphere model under the assumption of uniform uptake. The aims of this study were to determine the distribution of the absorbed dose delivered by ³²P on a patient-specific basis and to evaluate the accuracy with which this can be predicted from a pretherapy administration of ^99mTc-Sn colloid.

Methods

Three patients were treated with ³²P-chromic phosphate colloid following ^99mTc-Sn colloid administrations. Convolution dosimetry was performed using pretherapy and posttherapy sequential SPECT imaging, and verified with EGSnrc Monte Carlo radiation transport simulations. Mean absorbed doses to the cyst wall and dose–volume histograms were also calculated and compared with those obtained by the sphere model approach.

Results

Highly nonuniform uptake distributions of both the ^99mTc and ³²P colloids were observed and characterized by dose–volume histograms to the cyst wall. Mean absorbed doses delivered to the cyst wall, obtained with the convolution method, were on average 21 % (SD 18 %) and 50 % (SD 30 %) lower than those predicted by the ^99mTc distribution and the uniform assumption of the sphere model, respectively.

Conclusion

Absorbed doses delivered to the cyst wall by ³²P are more accurately predicted from image-based patient-specific convolution dosimetry than from simple sphere models. These results indicate the necessity to perform personalized treatment planning and verification for intracavitary irradiation of cystic brain tumours treated with radiocolloids. Patient-specific dosimetry can be used to guide the frequency and levels of repeated administrations and would facilitate data collection and comparison to support the multicentre trials necessary to progress this therapy.     

Application of jade samples for high-dose dosimetry using the EPR technique

The dosimeter characteristics of jade samples were studied for application in high-dose dosimetry. Jade is the common denomination of two silicates: jadeite and actinolite. The EPR spectra of different jade samples were obtained after irradiation with absorbed doses of 100 Gy up to 20 kGy. The jade samples present signals that increase with the absorbed dose (g-factors around 2.00); they can be attributed to electron centers. The EPR spectra obtained for the USA jade samples and their main dosimetric properties as reproducibility, calibration curves and energy dependence were investigated.     

Temperature effects on the ethanol-chlorobenzene dosimeter (Dvornik dosimeter)

The effects of elevated temperatures (50 and 80°C) on the dose dependence of the response of the ethanol-chlorobenzene (ECB) dosimeter, namely G(Cl⁻) values as a function of dose, were studied in the dose range 1–25 kGy. Systems containing 4, 10 and 20 vol% CB showed no dose effects of the response at 50°C and system containing 4 vol% CB showed no dose effect of G(Cl⁻) at 80°C, when compared with the radiation chemical yield measured for irradiations at room temperature (20°C). Dose dependence of G(Cl⁻) values in other systems at elevated temperatures were qualitatively similar to those at room temperature; the main difference, however, was that the values of G(Cl⁻) at elevated temperatures were higher. Larger temperature effects were observed at higher temperatures, higher CB concentrations and lower doses. Correct dosimetry is nevertheless possible with any formulation of the system at any dose or temperature within the studied interval by taking appropriate values of the response, either directly or by interpolation.     

用能量沉积核函数方法计算60Co照射野的吸收剂量

目的 介绍了用能量沉积核函数方法计算＾６０Ｃｏ照射野吸收剂理的方法。方法 能量沉积核函数方法将吸收剂量的贡献分为３部分：原射线、单次散射和多次散射。它使用基本的剂量学数据,如射野中心轴百分深度剂量、离轴比和淮直系统散射输出因子等,这些数据在Ｆｙｃ５０Ｈ治疗机上用方形照射野测量得到,再用能量沉积核函数计算吸收剂量,并讨论了散射线对吸收剂量的影响。结果 从测量数据得到了原射线和散射线的能量沉积核函数,并利用能量沉积核函数计算＾６０Ｃｏ照射野的主要剂量学参数。计算值和测量值是一致的;不规则照射野的吸收剂量及其分布的计算结果也和测量结果符合得很好。结论 能量沉积核函数方法适用于较精确地计算＾６０Ｃｏ不规则照射野的吸收剂量。     

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.     

Clinical application of GAFCHROMIC EBT film for in vivo dose measurements of total body irradiation radiotherapy.

The GAFCHROMIC EBT film model is a fairly new film product designed for absorbed dose measurements of high-energy photon beams. In vivo dosimetry for total body irradiation (TBI) remains a challenging task due to the extended source-to-surface distance (SSD), low dose rates, and the use of beam spoilers. EBT film samples were used for dose measurements on an anthropomorphic phantom using a TBI setup. Additionally, in vivo measurements were obtained for two TBI patients. Phantom results verified the suitability of the EBT film for TBI treatment in terms of accuracy, reproducibility, and dose linearity. Doses measured were compared to conventional dosimeter measurements using thermoluminescent dosimeters (TLDs), resulting in an agreement of 4.1% and 6.7% for the phantom and patient measurements, respectively. Results obtained from the phantom and patients confirm that GAFCHROMIC EBT films are a suitable alternative to TLDs as an in vivo dosimeter in TBI radiotherapy.     

Al2O3剂量计在准直60Co γ线中的吸收剂量响应

目的 用Monte Carlo法研究Al₂O₃剂量计在准直⁶⁰Co γ线照射下在水中的吸收剂量响应特性。方法 用EGSnrc/DOSRZnrc 程序计算水体模中Al₂O₃剂量计的吸收剂量及剂量计相应位置上水的吸收剂量,并计算吸收剂量换算因子。剂量计元件用一个直径0.4 cm高0.1 cm的圆柱形Al₂O₃薄片表示,计算深度0.5~8.0 cm,入射粒子是准直后的⁶⁰Co γ线。结果 在研究的深度范围内,吸收剂量换算因子变化不大,平均值为1.143±0.006,最大偏差不大于1.0%。结论 在研究范围内,⁶⁰Co γ线中Al₂O₃剂量计的吸收剂量响应与剂量计在水体模中的深度无关,剂量响应稳定。     

On line high dose static position monitoring by ionization chamber detector for industrial gamma irradiators

A 1 cm³ cylindrical ionization chamber was developed to measure high doses on line during the sample irradiation in static position, in a ⁶⁰Co industrial plant. The developed ionization chamber showed to be suitable for use as a dosimeter on line. A good linearity of the detector was found between the dose and the accumulated charge, independently of the different dose rates caused by absorbing materials.