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Port Glasgow, United Kingdom

Valeri G.,Clinical Radiology | Mari A.,Health Physics | La Riccia L.,AOU Ospedali Riuniti
Radiologia Medica

Purpose: This study was done to evaluate the appropriateness of dose indices in computed tomography (CT) by comparing the body computed tomography dose index (CTDI) and the size-specific dose estimates (SSDE) to determine which of these two parameters is more appropriate to estimate the radiation dose to both adult and paediatric patients. Materials and methods: We analysed 150 thoracic CT and 150 abdominal CT scans, half of which from adult patients and the other half from paediatric patients. We compared the values of the CTDIvol and the SSDE reporting the average, maximum and minimum percentage difference for each body region and depending on the age of the patients. Results: In the thoracic CT and abdominal CT scans, we found values of difference between the SSDE and the CTDIvol of 26.3 and 27.3 %, respectively, in adult patients and of 46.9 and 48.5 % in paediatric patients. Conclusions: The SSDE is a good tool for estimating the average radiation dose for a given patient depending on the input parameters and the dimensions of the specific person in question before a CT examination. © 2014, Italian Society of Medical Radiology. Source

Objective: Assessment of the potential doses to the hands and eyes for interventional radiologists and cardiologists can be difficult. A review of studies of doses to interventional operators reported in the literature has been undertaken. Methods: Distributions for staff dose to relevant parts of the body per unit dose-area product and for doses per procedure in cardiology have been analysed and mean, median and quartile values derived. The possibility of using these data to provide guidance for estimation of likely dose levels is considered. Results: Dose indicator values that could be used to predict orders of magnitude of doses to the eye, thyroid and hands from interventional operator workloads have been derived, based on the third quartile values, fromthe distributions of dose results analysed. Conclusion: Dose estimates made in this way could be employed in risk assessments when reviewing protection and monitoring requirements. Data on the protection provided by different shielding and technique factors have also been reviewed to provide information for risk assessments. Recommendations on the positions in which dosemeters are worn should also be included in risk assessments, as dose measurements from suboptimal dosemeter use can be misleading. © 2011 The British Institute of Radiology. Source

Abuhaimed A.,Beatson West of Scotland Cancer Center | Abuhaimed A.,University of Glasgow | Abuhaimed A.,King Abdulaziz City for Science and Technology | Martin C.J.,University of Glasgow | And 3 more authors.
Physics in Medicine and Biology

The IEC has introduced a practical approach to overcome shortcomings of the CTDI100 for measurements on wide beams employed for cone beam (CBCT) scans. This study evaluated the efficiency of this approach (CTDIIEC) for different arrangements using Monte Carlo simulation techniques, and compared CTDIIEC to the efficiency of CTDI100 for CBCT. Monte Carlo EGSnrc/BEAMnrc and EGSnrc/DOSXYZnrc codes were used to simulate the kV imaging system mounted on a Varian TrueBeam linear accelerator. The Monte Carlo model was benchmarked against experimental measurements and good agreement shown. Standard PMMA head and body phantoms with lengths 150, 600, and 900 mm were simulated. Beam widths studied ranged from 20-300 mm, and four scanning protocols using two acquisition modes were utilized. The efficiency values were calculated at the centre (εc) and periphery (εp) of the phantoms and for the weighted CTDI (εw). The efficiency values for CTDI100 were approximately constant for beam widths 20-40 mm, where εc(CTDI100), ε(CTDI100), and εw(CTDI100) were 74.7 ± 0.6%, 84.6 ± 0.3%, and 80.9 ± 0.4%, for the head phantom and 59.7 ± 0.3%, 82.1 ± 0.3%, and 74.9 ± 0.3%, for the body phantom, respectively. When beam width increased beyond 40 mm, ε(CTDI100) values fell steadily reaching ∼30% at a beam width of 300 mm. In contrast, the efficiency of the CTDIIECwas approximately constant over all beam widths, demonstrating its suitability for assessment of CBCT. εc(CTDIIEC), εp(CTDIIEC), and εw(CTDIIEC) were 76.1 ± 0.9%, 85.9 ± 1.0%, and 82.2 ± 0.9% for the head phantom and 60.6 ± 0.7%, 82.8 ± 0.8%, and 75.8 ± 0.7%, for the body phantom, respectively, within 2% of ε(CTDI100) values for narrower beam widths. CTDI100,w and CTDIIEC,w underestimate CTDI∞,w by ∼55% and ∼18% for the head phantom and by ∼56% and ∼24% for the body phantom, respectively, using a clinical beam width 198 mm. The CTDIIEC approach addresses the dependency of efficiency on beam width successfully and correction factors have been derived to allow calculation of CTDI∞. © 2014 Institute of Physics and Engineering in Medicine. Source

Abuhaimed A.,Beatson West of Scotland Cancer Center | Abuhaimed A.,University of Glasgow | Abuhaimed A.,King Abdulaziz City for Science and Technology | Martin C.J.,University of Glasgow | And 2 more authors.
Physics in Medicine and Biology

Many studies have shown that the computed tomography dose index (CTDI100) which is considered as a main dose descriptor for CT dosimetry fails to provide a realistic reflection of the dose involved in cone beam computed tomography (CBCT) scans. Several practical approaches have been proposed to overcome drawbacks of the CTDI100. One of these is the cumulative dose concept. The purpose of this study was to investigate four different approaches based on the cumulative dose concept: the cumulative dose (1) f(0,150) and (2) f(0,∞) with a small ionization chamber 20 mm long, and the cumulative dose (3) f100 (150) and (4) f100 (∞) with a standard 100 mm pencil ionization chamber. The study also aimed to investigate the influence of using the 20 and 100 mm chambers and the standard and the infinitely long phantoms on cumulative dose measurements. Monte Carlo EGSnrc/BEAMnrc and EGSnrc/DOSXYZnrc codes were used to simulate a kV imaging system integrated with a TrueBeam linear accelerator and to calculate doses within cylindrical head and body PMMA phantoms with diameters of 16 cm and 32 cm, respectively, and lengths of 150, 600, 900 mm. f(0,150) and f100 (150) approaches were studied within the standard PMMA phantoms (150 mm), while the other approaches f(0,∞) and f100 (∞) were within infinitely long head (600 mm) and body (900 mm) phantoms. CTDI∞ values were used as a standard to compare the dose values for the approaches studied at the centre and periphery of the phantoms and for the weighted values. Four scanning protocols and beams of width 20-300 mm were used. It has been shown that the f(0,∞) approach gave the highest dose values which were comparable to CTDI∞ values for wide beams. The differences between the weighted dose values obtained with the 20 and 100 mm chambers were significant for the beam widths<120 mm, but these differences declined with increasing beam widths to be within 4%. The weighted dose values calculated within the infinitely long phantoms with both the chambers for the beam widths≤140 were within 3% of those within the standard phantoms, but the differences rose to be within 15% at wider beams. By comparing the approaches studied in this investigation with other methodologies taking into account the efficiency of the approach as a dose descriptor and the simplicity of the implementation in the clinical environment, the f(0,150) method may be the best for CBCT dosimetry combined with the use of correction factors. © 2015 Institute of Physics and Engineering in Medicine. Source

Martin C.J.,Health Physics
Journal of Radiological Protection

Effective dose (E) is the only comparatively simple dose quantity that is related to health detriment for stochastic effects from exposure to ionising radiation. As such, E has found wide application for medical exposures, as it allows comparisons with doses from different examinations and other sources. E is derived from the weighted sum of doses to tissues known to be sensitive to radiation from epidemiological studies and contains inherent approximations. Thus it is not a scientific quantity, but a practical one that the International Commission on Radiological Protection (ICRP) has created for use in the calculation of reference doses for protection purposes. In the application of E to medical exposures, there has been a tendency to attribute a greater accuracy to values of E than is justified by its derivation. Recognising that E is strictly not subject to uncertainties, an analysis has been undertaken of potential uncertainties in E for different nuclear medicine examinations to enable users to judge its reliability as a comparator of relative risk. Assessments have been based on the considered accuracy of the component parts and indicate that the uncertainties in the values of E as a relative indicator of harm for nuclear medicine procedures for a reference patient are about 50%. These are larger than those for radiology procedures, because of the tendency for doses to single organs, especially the bladder, to form a substantial part of E for some procedures. Revision of the tissue weighting factors in 2007 produced a 10% decrease in the mean value of E for nuclear medicine examinations. Estimations of cancer risk based on E for an individual could vary by one or two orders of magnitude. E fulfils an important role as a health-related dose quantity that can be used in justification of nuclear medicine examinations, but physicians should be aware of its limitations. General terminology should be used in conveying risks to patients and medical professionals. © 2011 IOP Publishing Ltd. Source

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