Demonstration of enhanced iodine K-edge imaging using an energy-dispersive X-ray computed tomography system with a 25 mm/s-scan linear cadmium telluride detector and a single comparator

An energy-dispersive (ED) X-ray computed tomography (CT) system is useful for carrying out monochromatic imaging. To perform enhanced iodine K-edge CT, we developed an oscillation linear cadmium telluride (CdTe) detector with a scan velocity of 25 mm/s and an energy resolution of 1.2 keV. CT is performed by repeated linear scans and rotations of an object. Penetrating X-ray photons from the object are detected by the CdTe detector, and event signals of X-ray photons are produced using charge-sensitive and shaping amplifiers. The lower photon energy is determined by a comparator device, and the maximum photon energy of 60 keV corresponds to the tube voltage. Rectangular-shaped comparator outputs are counted by a counter card. In the ED-CT, tube voltage and current were 60 kV and 0.30 mA, respectively, and X-ray intensity was 14.8 μGy/s at 1.0m from the source at a tube voltage of 60 kV. Demonstration of enhanced iodine K-edge X-ray CT for cancer diagnosis was carried out by selecting photons with energies ranging from 34 to 60 keV.     

The diagnostic X-ray protection characteristics of Ytong, an aerated concrete based building material

Ytong is a widely used building material. The X-ray attenuation properties of Ytong for broad beam geometry conditions and for tube potentials in the 50-140 kVp range are investigated. Comparisons with published data for concrete and other building materials are made. The results suggest that Ytong is not suitable for primary X-ray shielding in common diagnostic installations. However, walls of Ytong, typically 15-20 cm thick, may offer adequate protection in dental and mammography installations, as well as in low workload diagnostic installations as a secondary barrier.     

Effective dose transmission of diagnostic X-rays through concrete and lead shields

When computing the amount of leakage from a diagnostic X-ray room, the transmission data of X-ray beams through the shielding material, which are used in the computation, must agree with the conditions of use of the X-ray equipment. Even if the tube potential is the same, the energy spectrum of generated X-rays depends on conditions such as high voltage rectification and total filtration, and transmission through the shielding material, too, is subject to change. In this paper, we propose a new method of calculation, which uses transmission data of mono-energetic photon beams computed by means of a Monte Carlo simulation, for obtaining effective dose transmission data through the shielding material of an X-ray beam with spectral distribution. We also present effective dose transmission data of primary X-ray beams and 90 degrees scattered X-ray beams through concrete and lead shields as determined by this method. This method, which can calculate the transmission data of X-ray beams with any spectral distribution, is useful in evaluating the leakage dose of diagnostic X-ray facilities.     

The effect of thin K-edge filters on radiation dose in dental radiography.

The use of thin K-edge filters has been found to reduce considerably the radiation dose in intra-oral radiography. The aim of this study was to investigate the effect of filtration on the skin entrance dose and several sites (representing organs or areas of interest within the head) along the central beam axis, at other points within the primary beam and at two points just outside the primary beam. The subject was a sliced head phantom (a human skull embedded in tissue-equivalent material) which was exposed to X rays from a conventional dental X-ray unit in the range of tube voltage 55-85 kVp for each of four filter systems. These were 2.7 mm of aluminium alone (the existing total filtration) or with an added 0.1 mm erbium, 0.1 mm yttrium or 0.05 mm niobium metal foils. Measurements of radiation dose were made using thermoluminescent dosemeters (TLD rods) and were adjusted to simulate the exposure resulting from a typical dental radiograph of a maxillary molar. The results suggest that the use of thin K-edge filters significantly reduces the entrance skin dose and to a certain extent reduces the total dose imparted to the head. However, the dose to the ipsilateral orbit at higher tube voltages may be increased.     

The diagnostic X-ray protection characteristics of Panelcrete, Aquapanel, Betopan and Gypsoplak Superboard

Panelcrete, Aquapanel and Betopan are cement-based building materials with uses similar to those of gypsum wallboard, whose properties as a diagnostic X-ray shielding material have been extensively studied. The X-ray attenuation characteristics of these cement-based boards as well as those of a gypsum wallboard, Gypsoplak Superboard, are investigated for broad beam geometry conditions and for tube potentials of 50 kVp, 70 kVp, 100 kVp, 125 kVp and 140 kVp. Comparisons between these materials as well as with published data for gypsum wallboard are made. An example of their use as secondary barriers is given. Furthermore, it is confirmed that when building materials are considered for diagnostic X-ray shielding, calculations based on data for similar materials and corrected for density differences can be used only as an approximation.     

Ambient dose during intraoral radiography with current techniques: part 3: effect of tube voltage

Objectives:This study was conducted to assess the impact of tube voltage on ambient dose during intraoral radiography, specifically remnant-beam transmission and scattered radiation.Methods and materials:Remnant-beam and scattered radiation doses were recorded using a phantom at tube voltages of 60, 63, 66 and 70 kV. Mathematical equations depicting their relations were then formulated, and reference values were calculated at the various voltages tested. Total ambient doses per exposure at 60 kV and at 70 kV were compared.Results:Both remnant-beam transmission and scattered radiation increased ~40% by increasing tube voltage from 60 kV to 70 kV, and the relation was linear. A remnant beam transmission reference value of 7.5% was established at 70 kV, as well as a conversion factor of 0.035 µSv/mAs at 1 m for scattered radiation at 60 kV. Given longer exposure times at 60 kV, total ambient dose proved higher at 60 kV than at 70 kV.Conclusion:Higher tube voltage results in higher remnant-beam transmission and more scattered radiation per workload. The relation is linear in the range between 60kV and 70 kV. Remnant-beam transmission at 70 kV is safely assessed at 7.5%. A conversion factor at 60 kV of 0.035 µSv/mAs at 1 m for the scattered radiation dose can be proposed. Total ambient dose per exposure was higher at 60kV than at 70 kV.     

Lead-rubber shielding effect on radiation dose to the gonads from a bilateral hand X-ray examination

IntroductionRecent guidance from the British Institute of Radiology (BIR) and the American Association of Physicists in Medicine (AAPM) focuses on cessation of patient Lead-rubber (Pb) shielding placed within the Field of View (FOV) that may influence image exposure or quality. Furthermore, the BIR assert shielding organs greater than 5 cm from the primary X-ray beam will have a negligible effect to the received radiation dose. Bilateral hand X-rays are frequently and repeatedly requested for the diagnosis and ongoing management of arthritic conditions. There is a lack of literature regarding the effect of Pb shielding during bilateral hand X-ray examinations. This research aimed to investigate the scattered secondary radiation dose to the gonads during a bilateral hand X-ray, with and without the use of Pb shielding outside the FOV at a greater distance than 5 cm from the primary beam.MethodsUsing an anthropomorphic phantom and constructed upper limbs, radiation was recorded to the male and female gonads. Thermoluminescent dosimeters (TLD's) (?" x ?" x 0.15″ TLD-100H) were placed in groups of three upon the testes and within the left and right ovary to record the ionising radiation dose. Three collimated exposures were completed using a standard clinical practice hand X-ray protocol of 60 kVp and 2.5 mAs with a source to image distance (SID) of 100 cm. The mean and standard deviation of the radiation dose was calculated for both with and without Pb shielding. A paired two-sample t-test was conducted to determine statistical significance (p ≤ 0.05).ResultsData analysis demonstrated dose measured to the testes of 5.3 μGy (SD 0.8) without Pb shielding and 2.3 μGy (SD 0.2) with Pb (reduction of 3 μGy; 56.6%). Left ovary doses measured 40.6 μGy (SD 1.2) without Pb shielding and 28.8 μGy (SD 1.7) with Pb (reduction of 11.9 μGy; 29.2%) and right ovary doses measured 39.5 μGy (SD 1.9) without Pb shielding and 26.6 μGy (SD 1.0) with Pb (reduction of 12.8 μGy; 32.4%). The paired two-sample t-test presented a statistically significant dose reduction (p = 0.0039).ConclusionThe study demonstrated dose limitation from scattered secondary radiation to the gonads when Pb shielding was used during a bilateral hand X-ray at distances greater than 5 cm from the primary X-ray beam on anatomy outside the FOV.Implications for practiceThe use of Pb shielding over the gonad area during a bilateral hand X-ray examination aligns to ALARP best practice and provides prospects for patient (male and female) dose reduction.     

Estimation of X-radiation protective coats in abdominal angiography

Medical personnel involved in abdominal angiography are exposed not only to direct radiation but also scattered radiation from inspection tables, patients, image intensifiers, and the beam-limiting system (collimator), among others. Japanese standard JISZ4831 prescribes protective coats of at least 0.25 mm lead equivalent, which is the uniform thickness of lead equivalent. The most commonly used protective coats are 0.25 mm Pb, 0.35 mm Pb, or 0.5 mm Pb in thickness. The weight of a typical protective coat is about 3 kg. While some coats weigh up to 6 kg, wearing such heavy coats becomes physically burdensome as inspection time increases. The trade-off between physical burden and protection was considered by analyzing the X-ray intensity distribution and attenuation rate of scattered radiation in each position assumed by the medical staff. In the case of inspections performed at an x-ray tube voltage of 80 kV, it may be possible to reduce the weight of the lead rubber apron by about 33%. Namely, the lead thickness can be reduced uniformly by 0.20 mm Pb at 70 cm and 0.05 mm Pb at 100 cm, when the shielding capability of a 0.25 mm thick Pb layer is accepted as the standard at 40 cm above the gonad position. The same range of permeated X-ray dose for the gonad position may be reduced as well. In the case of 110 kV, when the lead thicknesses are 0.30 mm Pb at 40 cm and 70 cm, and 0.10 mm Pb at 100 cm, it is possible to reduce the weight of the lead rubber apron by about 28%.     

The reduction in radiation dose for intra-oral radiographs by the use of thin K-edge filters

The aim of this investigation was to reduce the radiation dose to patients undergoing intra-oral dental radiography by using thin K-edge filters in addition to the existing aluminum filter. The subject was a head phantom (a human skull embedded in tissue-equivalent material), which was exposed to X rays over a range of tube voltages (50-90 kVp) for each of the four filter systems. These were 2.7 mm aluminium alone (the existing total filtration) or with added 0.1 mm erbium, 0.1 mm yttrium or 0.05 mm niobium. The radiation dose was measured at four selected sites along the primary beam. These were the entrance skin dose, the exit skin dose and intra-orally both in front and behind the dental film packet. The exposure times and radiation doses required to produce an equivalent density (degree of blackening) on a radiograph of an upper molar tooth were determined. Within the usual diagnostic range of 60-80 kV the use of the thin K-edge filter resulted in a doubling of the exposure time (owing to the additional attenuation of the added filters). However, the skin dose and the total dose imparted to the patient were significantly reduced.     

The dependence of the scattered radiation dose to personnel on technique factors in diagnostic radiology.

The measurement and prediction of scattered radiation dose to staff in diagnostic radiology is particularly important, owing to the increased use and complexity of interventional radiology. The air kerma-area product and scattered radiation dose in the vicinity of the patient couch, for both overcouch and undercouch X-ray tube geometries, were simultaneously monitored. The scattered radiation distribution at the couchside was deduced at a range of tube potentials for both overcouch and undercouch X-ray tube geometries. The variation of scattered radiation with field size on both geometries was investigated, as well as the variation with focus-table distance on an overcouch tube geometry. It was discovered that the scattered radiation dose at a point correlated with the air kerma-area product and the result may be used for radiation protection purposes. A method of predicting the scattered radiation dose at a given position is described.     

Exit dose studies in megavoltage photon therapy

A coin-shaped ionisation chamber, orientated with its thin window facing away from the radiation source, was used to investigate the dose perturbations caused by the absence of back-scattering material near the exit surface of solid phantoms. Cobalt 60 and 4, 8 and 16 MV X-ray beams were used in the study. With no scattering material beyond the chamber window the ionisation was found to be as much as 17% less than the full scatter value. This was attributed to the absence of both back-scattered electrons and back-scattered photons. Full electron back-scattering could be restored by placing between 1.0 and 2.7 mm of unit density material beyond the chamber, depending on the primary beam energy. Under these circumstances the reduction in dose, now due to the absence of back-scattered photons only, was found to be small.     

Evaluation of non-lead board as X-ray protective material

For security, boards containing lead are commonly used to partition off rooms adjacent to radiation facilities. From the viewpoints of environmental safety and of material recycling during the process of remodeling or repair, however, the trend is toward avoiding the use of lead-containing radiation-protection board. Consequently, we developed a lead-free board(W 910xH 1820xD 12.5 mm)composed of a mixed material incorporating calcium sulfate and barium sulfate to be used as a partition at a diagnostic X-ray institution. The mass attenuation coefficients of the lead-free board were lower by about 12% and 60% for energy ranges of 25 approximately 37 keV and 38 approximately 41 keV, respectively, as compared with those of lead. Lead equivalents for the newly developed board(12.5 mm thickness)were 0.87+/-0.01 mmPb at 100 kV tube voltage, 0.60+/-0.01 at 125 kV, and 0.47+/-0.01 at 150 kV. A double-layer lead-free board proved to have enough shielding ability even at usual photographic frequencies.     

螺旋断层加速器自屏蔽结构对机房屏蔽防护厚度的影响

目的 探讨新型放射治疗设备螺旋断层加速器机房的屏蔽计算方法以及该型加速器自屏蔽结构对机房屏蔽防护厚度的影响,为螺旋断层加速器机房的屏蔽防护设计提供依据.方法 根据国家相关标准要求,结合机房几何结构,分别计算无自屏蔽存在情况下屏蔽主射线、散射线和漏射线所需的屏蔽厚度;根据螺旋断层加速器自屏蔽特点以及其辐射场特性,计算自屏蔽存在情况下机房辐射防护屏蔽厚度.结果 有自屏蔽结构的螺旋断层加速器机房防护屏蔽体的厚度与没有自屏蔽结构相比,其计算结果差异有统计学意义(t=3.576,P＜0.05);主射束区包括南墙、北墙、顶棚和地板,自屏蔽结构可以分别减少约95.59%、63.63%、80.73%和51.30%的屏蔽厚度.结论 螺旋断层加速器自屏蔽结构可显著减少其机房主射束区所需的辐射防护屏蔽厚度.对有自屏蔽结构的加速器机房的屏蔽厚度,应该根据其辐射场数据进行计算,也可将无自屏蔽情况下主射束区的计算结果减去自屏蔽等效屏蔽材料厚度来估算.

Abstract：

Objective To study the calculation of the room shielding thickness of tomotherapy accelerator,a new type of radiotherapy facility,especially the impact of the beam block on the shielding design.Methods According to the relevant standards,combined with the room geometry,the shielding thickness was calculated without the presence of the beam block,considering the primary beam,the scattered beam and leakage.Meanwhile,the shielding thickness was also calculated as comparison with the presence of the beam block,based on the characteristics of tomotherapy facility and its radiation field.Results There was statistical difference between the shielding thicknesses calculated with the presence of the beam block and those without the beam block,to the primary beam direction including the south wall,north wall,the roof and the floor,the shielding thickness were decreased by 95.59%,63.63% ,80.73%and 51.30% ,respectively.Conclusions For the tomotherapy accelerator,the beam block could be of great help to minify the shielding thickness of the room.The radiation field of the tomotherapy facility could be used for the calculation to improve accuracy,and the shielding thickness can also be estimated by subtracting the initial shielding thickness without beam block of the beam block equivalent thickness in the primary beam direction alternatively.     

A model for calculating shielding requirements in diagnostic X-ray facilities

In this study a new model for calculating shielding requirements in diagnostic X-ray facilities is presented. It is based on the combination and modification of models and concepts originally proposed by other authors in order to calculate barrier requirements in diagnostic X-ray facilities accurately and realistically without unjustified exaggerations. With this model, multiple sources of radiation operating at different potentials, leakage radiation reduction when operating at potentials less than the maximum rated value, secondary radiation use factors reduction for primary barriers, attenuation by image receptor hardware and existing building materials are all taken into account. Examples of shielding calculations for typical cases are given illustrating the differences between the various models and concepts proposed, as well as the potential reduction in shielding requirements without compromising the radiation protection of public and staff.     

Estimation of X-ray beam quality by electron paramagnetic resonance (EPR) spectroscopy

A novel dosimetry-based technique using EPR spectroscopy to determine X-ray beam quality is proposed. The radiation-sensitive material is made of a mixture of two polycrystalline substances with different X-ray absorption properties.

The composite samples, consisting of polycrystalline lithium formate monohydrate and calcium formate, were prepared as pellets, X-irradiated, and analyzed with EPR spectroscopy. The ratio of the EPR signal amplitudes of the two constituents can serve as a measure of the X-ray beam quality given by the equivalent photon energy. The calculation of the signal amplitude ratio involves a reconstruction of the composite EPR spectrum. The logarithm of the signal amplitude ratio appears to be linearly correlated with the logarithm of the equivalent photon energy. The linear relationship can be used as a calibration for estimating the equivalent photon energy from the composite EPR spectrum.

The composite material was used to investigate the changes in the equivalent photon energy in a Perspex phantom with increasing depth. When a 220 kV X-ray beam with an equivalent photon energy of about 100 keV was used, changes in the EPR signal amplitude ratio revealed a buildup of scattered photons with increasing depth in the phantom. This change could be related to the equivalent photon energy using the logarithmic calibration curve. It was found that the equivalent photon energy at the depth of 13 cm in the phantom was 25% lower than on its surface.

The proposed method can be used for estimating equivalent photon energy in both standardized and non-standardized situations, the latter corresponding to beam setups where use of filters and ionization chambers is difficult or impossible. Also, the system can provide a means for measuring photon energy in X-irradiated phantoms.     

Radiation exposure during examination with a therapy simulator. 2. Radiation load on the examiner during radiography (measurements on the Alderson-Man phantom)]

In judging the risk incurred by persons professionally exposed to radiation, there is at present a more distinct tendency towards consideration of somatic effects - as e.g. somatic "crossing over", accidents of development, induction of cancer; thus more attention is paid to individual risk. For assessment of this radiation risk, the organ doses in question must be known; they can be estimated by means of the ascertained tissue-air-ratios, if the field of stray radiation from the X-ray equipment is known. To obtain data for statements with regard to the radiation load on the examiner during radioscopies with a therapy simulator, it was necessary to determine the stray radiation field of the X-ray apparatus. Therefore, using an Alderson-Man-phantom, the angular distribution of the local dose rate were measured at a tube voltage of 84 kV. The skin irradiation fields had dimensions of 25 cm2, 100 cm2, and 400 cm2 at the distances 50 cm, 100 cm, 150 cm, and 200 cm of the ionization chamber from the central ray. The measurements were performed on levels of 90 cm, 130 cm, and 160 cm above the floor. Some additional measurements aimed at a more exact investigation of the dependency of scattered radiation upon the tube voltage, the area of the radiation field, the distance from the central ray, and the height above the floor. The attenuation capacity of a light radioprotective apron (0.25 mm lead equivalence) was also determined. It turned out that, at a tube voltage of 84 kV, the apron still was passed by about 3.6% of the hitting stray radiation. The present measurements yield important indications of the best possible locations of the examiner during radioscopy. A practical example is given showing how to assess the radiation load on single organs; the results show that the examiner is exposed to a gonadal load of about 2 mR and to a load of about 17 mR on the crystalline lenses, while engaged in preparative roentgenologic measures for intrauterine transfusions.     

Absorbed dose behind eye shields during kilovoltage photon radiotherapy

The absorbed dose at the position of the lens of the eye under lead or tungsten eye shields during kilovoltage photon radiotherapy is critically dependent not so much on the thickness of the eye shield itself as on the size of the treatment field and the diameter of the shield used. Whilst dose from primary photons is easily attenuated to relatively insignificant levels by a few millimetres of lead or tungsten, scattered photons from outside the shielded area can provide over 25% of the prescribed dose. Since backscatter factors do not increase monotonically with photon energy, it is not safe to assume that the highest photon energy used will provide the highest dose. A simple method to estimate the dose under an eye shield based on tabulated backscatter factors is shown. Measurements under commercially available eye shields were made to verify the expression and to determine the attenuation of primary photons. Predicted and measured absorbed dose under the eye shields were found to agree to within 1% of the prescribed dose. The relative dose due to primary photons beneath the eye shields was found to be less than 0.1% and 0.5 (+/-0.1)% for the 150 kV and 260 kV beams, respectively. This is considerably less than the dose from backscattered radiation.     

The intensity of scattered radiation in mammography

The ratio of scattered-to-primary radiation has been measured for a range of x-ray tube voltages, field sizes and phantom thicknesses that typify clinical mammographic situations. The relative intensity of scattered radiation measured was essentially independent of kVp but increased as the phantom thickness and radiation field size increased. For the range of field sizes and phantom thicknesses that typify clinical situations the intensity of scattered radiation varied from about 40 to 85% of the primary beam intensity indicating that only from about 54 to 71% of the primary beam contrast is imaged in mammography.     

Computed tomography of the head: An experimental study to investigate the effectiveness of lead shielding during three scanning protocols

PurposeThe purpose of this experimental study, carried out in 2002, was to investigate the effectiveness of lead shielding during three scanning protocols for Computed Tomography (CT) head examinations.During CT, the thyroid is irradiated via scattered radiation outside the primary beam. Scientists have proved a definite link between thyroid cancer and radiation but have struggled to quantify the risks from low doses such as those in medical exposures. Children are known to be at higher risks from the effects of radiation than adults.MethodAn anthropomorphic phantom was used to simulate the patient. Shielding in the form of a standard lead thyroid shield was used due to the nature of the rotating X-ray beam involved with CT. Thermoluminescent detector chips were used to measure the approximate dose to the thyroid with and without the application of the shield.ResultsThe effectiveness of shielding varied with scanning technique, as did the thyroid dose due to scattered radiation. The lead shield significantly reduced the dose to the thyroid by 46–58% at the surface of the thyroid and by 37–44% within the thyroid tissue at 1 cm depth.ConclusionIn light of the increasing number of CT scanners, and the fact that head scans account for 50% of all CT examinations and 25% of the collective dose from CT to the UK population, it is important that all methods of dose reduction are considered. The use of shielding is a simple yet effective method of dose optimisation that has not been extensively investigated.     

Eine Spezialabschirmung für die Strahlentherapie von Schwangeren

PURPOSE: Measurement of the radiation dose of different radiotherapy techniques with a phantom at the position of the uterus of a pregnant patient with and without a special radiation shielding. MATERIAL AND METHODS: A special radiation shielding for the radiation therapy of a pregnant patient was constructed in the shape of a tunnel over the abdomen from 1 cm thick lead to reduce scatter radiation to the uterus and the fetus therein. The reduction of the scatter radiation to the lower abdomen was measured for three typical cases (cerebrum with lateral opposed fields, 6-MV photons; tangential fields for mamma irradiation, 6 MV; and anteroposterior-posteroanterior [AP-PA] opposed fields of 15 MV for treatment of the mediastinum) at an anthropomorphic Alderson phantom with thermoluminescence dosimeters in different depths and with an ionization chamber positioned in an RW3 solid water phantom. In the case of lateral opposed fields, a movable lead wall was additionally positioned next to the accelerator's head to reduce the scatter radiation from this source. RESULTS: Depending on the geometry of the radiation fields and on the photon energy, a reduction of the dose to the lower abdomen averaged over the depths of 6, 9, and 12 cm from 16% (15 MV, mediastinum case) to 51% (6 MV, cerebrum with additional lead wall) was achieved. The absolute scattered dose with shielding in place for a 2-Gy fraction dose results to 3.85 mGy and 0.27 mGy, respectively. CONCLUSION: National and international recommendations on the radiation dose to a fetus of a pregnant patient state limits of 200 mSv (DGMP report no. 7) and 100 mGy (ICRP 84), below which an abortion should not be considered and above which an indication for termination of the pregnancy could be given, respectively. The dose to the fetus can be kept below these limits with the shielding described in this work. Therefore, a radiation therapy of a pregnant patient is possible when these special precautions to reduce the scatter radiation to the fetus are met.