Mammography dosimetry using an in-house developed polymethyl methacrylate phantom

Phantom-based measurements in mammography are well-established for quality assurance (QA) and quality control (QC) procedures involving equipment performance and comparisons of X-ray machines. Polymethyl methacrylate (PMMA) is among the best suitable materials for simulation of the breast. For carrying out QA/QC exercises in India, a mammographic PMMA phantom with engraved slots for keeping thermoluminescence dosemeters (TLD) has been developed. The radiation transmission property of the developed phantom was compared with the commercially available phantoms for verifying its suitability for mammography dosimetry. The breast entrance exposure (BEE), mean glandular dose (MGD), percentage depth dose (PDD), percentage surface dose distribution (PSDD), calibration testing of automatic exposure control (AEC) and density control function of a mammography machine were measured using this phantom. MGD was derived from the measured BEE following two different methodologies and the results were compared. The PDD and PSDD measurements were carried out using LiF: Mg, Cu, P chips. The in-house phantom was found comparable with the commercially available phantoms. The difference in the MGD values derived using two different methods were found in the range of 17.5-32.6 %. Measured depth ranges in the phantom lie between 0.32 and 0.40 cm for 75 % depth dose, 0.73 and 0.92 cm for 50 % depth dose, and 1.54 and 1.78 cm for 25 % depth dose. Higher PSDD value was observed towards chest wall edge side of the phantom, which is due to the orientation of cathode-anode axis along the chest wall to the nipple direction. Results obtained for AEC configuration testing shows that the observed mean optical density (O.D) of the phantom image was 1.59 and O.D difference for every successive increase in thickness of the phantom was within±0.15 O.D. Under density control function testing, at -2 and -1 density settings, the variation in film image O.D was within±0.15 O.D of the normal density setting '0' and at +2 and +1 density setting, it was observed to be within±0.30 O.D. This study indicates that the locally made PMMA TLD slot phantom can be used to measure various mammography QC parameters which are essentially required for better outcomes in mammography.     

Filtered X ray beam dosimetry from 10(-3) to 10(2) Gy dose range by using phototransistors

Low-cost, commercially available phototransistor-type semiconductor devices have been tested for monitoring filtered X ray beam dose. A Pantak X-ray unit was used to generate aluminium filtered X ray beams from 60 to 120 kV potentials. The analysis of the radiation detection behaviour as a function of the X ray tube parameters (peak kilovoltage and electrical current) are presented. The changes of the phototransistor electronic parameters have been evaluated and the results indicate that phototransistors can be used as X ray detectors for dose estimation in two different ways: electrical current read-out from 1 to 100 mGy dose range, and the changing of the radiation detection sensitivity in the dose range from 0.1 to 100 Gy. In addition, the devices show high reliability with no sign of substantial performance degradation with use and, in certain dose ranges, the cumulative dose evaluations could be performed up to 10,000 times with no need for re-calibration.     

Radiophotoluminescence dosimetry using a small spherical glass: a preliminary phantom study

A radiophotoluminescence dosimetry has been proposed using a spherical silver-activated phosphate glass with a diameter of 1.5 mm. A 6 MV photon dose of 2 Sv (2 Gy) was delivered to 14 spherical glass samples placed between two solid water phantoms at a depth of 10 cm. The samples were positioned within a 20 x 20 mm(2) centred at beam axis to ensure uniform dose absorption. A normalised output from a read-out system was obtained by simultaneously measuring luminescence from a non-irradiated reference and that from an irradiated reference to eliminate background contamination and time-varying fluctuation of the readout system, leading to a normalised standard deviation of 1.8%. A dose up to 3.5 Sv (3.5 Gy) was delivered to three spherical glass samples positioned between two solid water phantoms at a depth of 10 cm. The normalised output increased linearly with the applied dose.     

Potential for optimisation of paediatric chest X-ray examination

The purpose of this study was to compare the important aspects of paediatric radiological practice and the patient doses from chest X-ray examinations performed in three hospitals in Bulgaria. Data from 163 paediatric patients were recorded using a standardised form. Entrance surface air kerma (ESAK) to patient was calculated from the air-kerma air product (KAP) and field size measurements. Large variations were found for KAP and ESAK. Inappropriate film size and insufficient collimation were often used. Inappropriate use of automatic exposure control and antiscatter grid was found. In most cases, no attention was paid to reduce dose to sensitive organs by means of shielding or proper collimation. Recommendations were given to the hospitals on how to reduce patient doses in paediatric chest radiography.     

Alanine and TLD coupled detectors for fast neutron dose measurements in neutron capture therapy (NCT)

A method was investigated to measure gamma and fast neutron doses in phantoms exposed to an epithermal neutron beam designed for neutron capture therapy (NCT). The gamma dose component was measured by TLD-300 [CaF2:Tm] and the fast neutron dose, mainly due to elastic scattering with hydrogen nuclei, was measured by alanine dosemeters [CH3CH(NH2)COOH]. The gamma and fast neutron doses deposited in alanine dosemeters are very near to those released in tissue, because of the alanine tissue equivalence. Couples of TLD-300 and alanine dosemeters were irradiated in phantoms positioned in the epithermal column of the Tapiro reactor (ENEA-Casaccia RC). The dosemeter response depends on the linear energy transfer (LET) of radiation, hence the precision and reliability of the fast neutron dose values obtained with the proposed method have been investigated. Results showed that the combination of alanine and TLD detectors is a promising method to separate gamma dose and fast neutron dose in NCT.     

Chest radiography: a comparison of image quality and effective dose using four digital systems

Image quality (IQ) and effective dose for chest radiography was compared for four digital imaging systems that used three different detector technologies: a-Si/TFT flat-panel detector (FPD), scanning-slot/charge-coupled device (CCD) and photostimuable phosphor (PSP). On each system a phantom was exposed at 125 kV(p) for automatic exposure control (AEC) and 2, 4 and 8 Gy receptor dose using identical geometrical conditions. All images were scored as softcopy images by three observers. The effective dose was calculated for each exposure condition. For AEC, superior IQ was observed for the GE FPD compared with all the other systems, which showed similar IQ performance. For all systems the entrance surface dose associated with AEC was within the European recommendations but variations in the effective dose were observed between the four systems. For identical receptor dose levels superior IQ was observed with the FPDs. Thorascan was noted for its low effective dose and Agfa CR was associated with the highest effective dose. FPD systems showed a better overall performance, followed by the CCD and PSP systems.     

直接数字化X线摄影技术

数字X线摄影是指利用电子计算机数字化潜能与常规X线摄影及装置相组合，将其X线信息转换成数字形式，经后处理成像的方法。 直接数字X线摄影是在上述基础上省略信息采集中的中间传递环节，具有成像快，影像质量高的特征。 本文对直接数字化成像技术的特点、构造、工作原理、影像质量等进行概述。     

Highly sensitive thermoluminescent carbon doped nanoporous aluminium oxide detectors

In this work we present the synthesis, characterisation and the thermoluminescence (TL) response of nanoporous carbon doped aluminium oxide Al2O3:C produced by anodic oxidation of aluminium in organic and inorganic solvents. The X-ray and scanning electron microscopy (SEM) measurements reveal that the synthesised samples are amorphous and present highly ordered structures with uniform pore distribution with diameter of the order 50 nm. The photoluminescence and spectroscopic analysis in the visible and infrared regions show that the luminescence properties presented by the samples prepared in organic acid are due to carboxylate species, incorporated in anodic alumina films during the synthesis process. After an annealing treatment, part of the incorporated species decomposes and is incorporated into the structure of the aluminium oxide yielding a highly thermoluminescent detector (TL) . The results for X-ray irradiation in the range from 21 to 80 keV indicate a linear TL response with the dose in the range from 5 mGy to 1 Gy, suggesting that nanoporous aluminium oxide produced in the present route of synthesis is a suitable detector for radiation measurements.     

Ti（CN）－Al_2O_3复合陶瓷与金属摩擦副的摩擦学特性研究

本文对水及油润滑条件下Ｔｉ（ＣＮ）－Ａｌ２Ｏ３复合陶瓷与纯铝、纯铁及不锈钢三种金属的摩擦、磨损特性进行了研究．在两种条件下，随着载荷及速度的增加，三种摩擦副的磨损量均明显增大．但两种润滑条件下的变化趋势稍有差别，水润滑时摩擦副的磨损量比油润滑时的大．与干摩擦时的试验结果相比，水或油的存在不仅没起到减磨作用，反而使磨损加剧．能谱分析结果表明，两种润滑情况下，金属与陶瓷间均有材料的转移或扩散发生，但水润滑时摩擦副材料间相互转移的量比油润滑时更大．     

Evaluation of paediatric X-ray doses in Moroccan university hospitals

This work evaluates the entrance skin dose (ESD), the body organ dose (BOD) and the effective dose (E) for chest X-ray exposures of paediatric patients. Two Moroccan university hospitals in Rabat, composed of two departments, and one in Casablanca with one paediatric compartment has been considered. For reasons of confidentiality, the departments are named A, B and C. Patients were divided into four age groups: 0-1, 1-5, 5-10 and 10-15 y, so that the results could be compared with previous published data found in the literature. The results have been calculated with the use of the Dose Cal software. Results of mean ESD for the age interval 1-5 y and antero-posterior (AP) projection are: 162 μGy for hospital A, 91 μGy for hospital B and 105 μGy for hospital C. The diagnostic reference levels (DRLs) of 100 μGy for this age range is exceeded in hospital A, while in the other two hospitals results were within the DRL and comparable with the results found in Brazil, Soudan, Nigeria and other radiological centres inpean Countries. The results of BOD and E showed that for the three departments, the BOD varies in the same proportion as the ESD. The highest values are those of hospital A. For the PA examination, the dose is reduced compared with the AP projection, especially for sensitive organs.     

Patient and personnel dosimetry in endovascular radiotherapy with 90Sr/90Y sources

Endovascular brachytherapy (EVBT) is an established treatment to reduce the probability of restenosis after a percutaneous coronary intervention. The purpose of this study was to assess (1) the manufacturer's stated dosimetric data for (90)Sr/(90)Y source trains to be used in EVBT and (2) the procedure-related radiation burden. The radiation fields in water around six (90)Sr/(90)Y source trains were studied using phantoms made of 'solid water' and MD55-2 radiochromic films. The water equivalence of the phantom material was tested by applying quantitative computed tomography. Thermoluminescence dosemeters were used to assess personal radiation burden and crosscheck the dose distribution along the source trains. Technical failure was observed in one source train and this train was excluded from analysis. The measured dose rate in water at 2 mm radial distance was on average 8% higher than the manufacture's stated value (range of measured to stated values 1.05--1.15). The dose rate decreased exponentially with radial distance between 2 and 6 mm. The dose rate in contact with the source viewing window of the delivery devices ranged between 0.5 and 7.5 mGy h(-1). Low-energy photons were the main contributors to personal dose.     

The 2002 dosimetry system (DS02) and available fluences for organ dose calculations

The A bomb dosimetry system (DS) calculates each survivor's organ doses. It does this by calculating the angular fluences incident on each survivor. These are used with humanoid phantom shielding calculations to estimate organ doses in 15 organs, 3-sized phantoms, 2 sexes and 2 postures at any orientation or distance to the bomb. The DS has been re-used and updated several times. Currently, efforts are being considered to include shielding for additional organs by adding additional phantoms. The DS has gone through a series of upgrades referred to as: DS84, DS86, DS86R, DS93, DS02. DS86 and DS02 were approved and installed at Radiation Effects Research Foundation. The system uses free-field energy-angular fluence from a discrete ordinate calculation coupled with Monte Carlo adjoint-shielding histories. This paper briefly discusses the adjoint Monte Carlo; combinatorial shield geometry for the phantom, house, factory, and terrain; modifications to use fictitious scattering in voxel phantoms; the adjoint source energy, angle and location distribution; 'leakage histories' and their optimisation for dose or fluence; doubly differential (energy-angle) coupling for single-, double-, or triple-shielding coupling; output of various components of dose and energy-angular fluences; survivor-specific inputs; organ dose uncertainty; and testing, benchmarking and extended applications. Also, approaches to add additional organ-shielding calculations to DS02 are discussed.     

Monte Carlo calculation of radiation dose in CT examinations using phantom and patient tomographic models

By using a voxel-based Monte Carlo simulation technique, we developed and validated a method to calculate radiation-absorbed dose in the computed tomography (CT) examinations from the images of phantoms and patients. The ionising radiation transport was simulated using the EGS4 code system. The geometry of the X-ray beam (focus-to-axis distance, field of view, collimation, and primary and beam-shaper filtration) and the X-ray spectral distribution (HiSpeed LX/i) were included in the simulation. Each axial CT image was reduced to a 256 x 256 matrix and stacked in a volume. The patient images were segmented before the simulation of radiation transport by using four categories of materials, such as air, lung, muscle and bone. To test the voxel-based method, the values of the radiation dose derived from a simulated CT exposure were calculated and compared with those obtained from the measurements performed within the dosimetry phantoms. To complete the scope of the work, series of CT scans of the trunk of an anthropomorphic phantom and patients were simulated to calculate the average dose in each 1-cm-wide transverse slice (ADS). The comparison between the simulated and measured dose data for the CT indices showed a difference of <5% in all the cases. The estimated mean values of ADS from the chest, abdomen and pelvis of the anthropomorphic phantom were approximately 1.7-2 times the weighted CT dose index (CTDI(w)) value, whereas the mean ADS values for these anatomical areas were 1.3-2 times the CTDI(w) of patients. The voxel-based simulation method provided a technique for estimating the individual patient doses in the CT examinations.     

Environmental radioactivity studies in the proposed Lambapur and Peddagattu uranium mining areas of Andhra Pradesh, India

The present work was aimed at the establishment of baseline radioactive data in the proposed Lambapur and Peddagattu uranium mining areas in the Andhra Pradesh state, India. The background concentrations of naturally occurring radioactivity in the near-surface soils of the study areas were estimated and the results were analysed. The (238)U concentration in the near-surface soil of the study area was found to vary from 100 to 176 Bq kg(-1), with a mean of 138±24 Bq kg(-1). (232)Th in the study area soils was found to vary between 64 and 116 Bq kg(-1), with a mean of 83±15 Bq kg(-1). The (40)K concentration was found to vary between 309 and 373 Bq kg(-1), with a mean of 343±20 Bq kg(-1). The mean natural background radiation levels were also measured with thermoluminescence (TL) dosimetry technique and with a μR-survey meter, in the villages of the study area. Dose rates measured by TL are found to vary from 1287 to 3363 μGy y(-1), with a mean of 2509 ± 424 μGy y(-1). The dose rates measured in the same villages with a μR-survey meter were found to be in the range of 1211-3255 μGy y(-1), with a mean of 2524 ± 395 μGy y(-1). The mean radiation levels in the study area are found to be relatively high when compared with (Indian) national and international averages. Correlations among radon, thoron and gamma dose rates were found to be poor. The pre-operational data produced in this work will be useful for comparison with future radiation levels during the proposed uranium mining operations.     

Y对Mg-14Al-5Si合金性能的影响

使用扫描电子显微镜(SEM)、能量色散光谱仪(EDS)、光学显微镜(OM)及X射线衍射仪(XRD)等手段分析了Mg-14Al-5Si合金的组织和成分,用布洛维硬度计和电子万能试验机测试了这种合金的力学性能,研究了在Mg-14Al-5Si合金中添加不同量的Y元素对其组织和力学性能的影响。结果表明：在Mg-14Al-5Si合金中分别添加0.5%、0.8%、1.0%和1.5%(质量分数,下同)的Y元素,使合金中的Mg₂Si相由粗大的树枝状变为多边形和圆形,共晶β-Mg₁₇Al₁₂相由粗大的连续网格状变为细小的网格状和孤岛状。Y的添加量为1.0%时改性效果最佳,Mg₂Si相的平均尺寸由42.21 µm减小到8.15 µm,此时合金的力学性能最佳,硬度为135 HB,抗拉强度为147 MPa,屈服强度为76 MPa,伸长率为5.04％。在Y的添加量为1.5%的合金中发现白色块状的Mg-Si-Y化合物。Y元素能促进Mg₂Si相形核、抑制其各向异性生长,并在β-Mg₁₇Al₁₂相的生长前沿偏析形成过冷结构,抑制其生长。     

Dose measurement for medical staff with glass dosemeters and thermoluminescence dosemeters during 125I brachytherapy for prostate cancer

Photoluminescence glass dosemeters (PLDs) and thermoluminescence dosemeters (TLDs) are commonly used as a personal monitoring dosemeter. PLDs and TLDs were used for surface dose monitoring of medical staff involved in (125)I brachytherapy for prostate cancer because these dosemeters have a wide dose-response linearity and high sensitivity for low photon energy. Surface doses measured with PLDs agreed with those with TLDs within ～20 % except for a few cases. Surface doses at a surgeon's left hand and arm were higher than those at the other measuring points. A surgeon received a maximum dose of 650 μGy at the back of left hand. Surface doses to an assistant were <100 μGy. Surface doses to a nurse, a radiologist, an anaesthesiologist and a radiological technologist were <10 μGy. The occupational exposure to a surgeon could be reduced by the adjustment of fluoroscopic parameters and the use of lead gloves.     

Mechanochemically activated aluminium: Preparation, structure, and chemical properties

Mechanical treatment of aluminium with 10-30 wt% graphite in the high-energy vibration mills leads to the formation of a chemically active substance. The structure of active aluminium and its formation are investigated by X-ray diffraction, adsorption, chemical analysis, and DSC. The reactivity of active Al is checked in reactions with graphite, as well as water, oxygen, and nitrogen. At the initial stage of mechanochemical interaction of aluminium with graphite, the dispergation of components and accumulation of defects in Al and C take place. Simultaneously, the surfaces of aluminium nanoparticles are covered with the carbon layer. Then the chemical interaction of aluminium with carbon starts on the surface of particles. At the final stage, aluminium carbide is formed in the volume of particles. The maximal reactivity of Al corresponds to the Al/C nanocomposites, in which chemical interaction of components is not yet realized. The reactivity of mechanochemically activated aluminium significantly exceeds that of standard aluminium powders. Interaction of activated Al with carbon takes place at 450°C, which is 800°C lower than the temperature at which the nonactivated aluminium reacts with carbon. Two types of reactions (“isothermal” and explosive) are observed for mechanochemically activated Al with water and air.     

A study of environmental radioactivity measurements for Cankiri, Turkey

This study is the first to assess the level of background radiation for the Cankiri province of Turkey. Indoor air radon concentrations were determined using Columbia Resin-39 nuclear track detectors and the average (222)Rn activity was found to be 44 Bq m(-3) (equivalent to an annual effective dose of 1.1 mSv). Measurements of gamma doses in outdoor air were performed using a portable plastic scintillation detector and the average gamma absorbed dose rate was found to be 8 μR h(-1) (corresponding to an annual effective dose of 87.7 μSv). Radionuclide activity concentrations in soil samples were measured through gamma-ray spectrometry and the average activities were determined as 17.7, 22.3, 357 and 4.1 Bq kg(-1) for the radionuclides (238)U, (232)Th, (40)K and (137)Cs, respectively. The average annual effective dose from the natural radioactivity sources ((238)U series, (232)Th series and (40)K) was calculated to be 44.4 μSv. Radioactivity levels of drinking water samples were carried out using a low-background proportional counter and the average gross alpha and beta activities were obtained as 0.25 and 0.26 Bq l(-1), respectively (equivalent to an annual effective dose of 184 μSv). The average radon concentrations in indoor air and the average radionuclide activities in soil were found to be lower than most Turkish cities while higher levels of outdoor gamma dose rate and water radioactivity were observed. The results of this study showed that the region's background radioactivity level differs considerably from the reported data for Turkish cities.     

Towards a proposition of a diagnostic (dose) reference level for mammographic acquisitions in breast screening measurements in Belgium

A diagnostic reference level (DRL) is a dose level for a typical X-ray examination of a group of patients with standard body sizes and for broadly defined types of equipment. These levels are expected not to be exceeded for standard procedures when good and normal practice regarding diagnostic and technical performance is applied. In this paper, we have calculated DRLs for screening mammography in Belgium. The 95th percentile of the mean average glandular dose is 2.46 mGy. The DRL based on polymethyl methacrylate (PMMA) measurements was 2.08 mGy. Correlation coefficient (R) between doses from patient studies and phantom studies was 0.90, with an average underestimation of the phantom measurements of 15% for systems that use only Mo/Mo anode/filter. For the centres that use other anode/filters, there is not enough scientific evidence that a single phantom measurement of a standard PMMA block is representative for the patient dose.     

Technical performance of the Luxel Al(2)O(3):C optically stimulated luminescence dosemeter element at radiation oncology and nuclear accident dose levels

The dose ranges typical for radiation oncology and nuclear accident dosimetry are on the order of 2-70 Gy and 0.1-5 Gy, respectively. In terms of solid-state passive dosimetry, thermoluminescent (TL) materials historically have been used extensively for these two applications, with silver-halide, leuco-dye and BaFBr:Eu-based films being used on a more limited basis than TL for radiation oncology. This present work provides results on the performance of a film based on an aluminum oxide, Al(2)O(3):C, for these dosimetry applications, using the optically stimulated luminescence (OSL) readout method. There have been few investigations of Al(2)O(3):C performance at radiation oncology and nuclear accident dose levels, and these have included minimal dosimetric and environmental effects information. Based on investigations already published, the authors of this present study determined that overall improvements over film and TLDs for this Al(2)O(3):C OSL technology at radiation oncology and nuclear accident dose levels may include (1) a more tissue-equivalent response to photons compared to X-ray film, (2) higher sensitivity, (3) ability to reread dosemeters and (4) diagnostic capability using small-area imaging. The results of the present investigation indicate that additional favourable performance characteristics for the Al(2)O(3):C dosemeter are a wide dynamic range (0.001-100 Gy), a response insensitive to temperature and moisture over a wide range, negligible dose rate dependence, and minimal change in post-irradiation response. As a radiation detection medium, this OSL phosphor offers an assortment of dosimetry properties that will permit it to compete with current radiation detection technologies such as silver-halide, leuco-dye and photostimulable-phosphor-based films, as well as TLDs.