For CT coronary angiography (CTCA), a generic chest conversion factor returns a significant underestimate of effective dose. The aim of this manuscript is to communicate new dosimetry methods to calculate weighted CT dose index (CTDIw), effective dose, entrance surface dose (ESD) and organ dose to the breast for prospectively gated CTCA.CTDIw in 32 cm diameter Perspex phantom was measured using an adapted technique, accounting for the segmented scan characteristic. Gafchromic XRCT film (International Speciality Products, New Jersey, NJ) was used to measure the distribution and magnitude of ESD. Breast dose was measured using high sensitivity metal oxide semiconductor field-effect transistors and compared to the computer based imaging performance assessment of CT scanners (ImPACT) dosimetry calculations.For a typical cardiac scan the mean ESD remained broadly constant (7-9 mGy) when averaged over the circumference of the Perspex phantom. Typical absorbed dose to the breast with prospectively gated protocols was within the range 2-15 mGy. The subsequent lifetime attributable risk (LAR) of cancer incidence to the breast was found at 0.01-0.06 for a 20-year-old female. This compares favourably to 100 mGy (LAR ~0.43) for a retrospectively gated CTCA.Care must be taken when considering radiation dosimetry associated with prospectively gated scanning for CTCA and a method has been conveyed to account for this. Breast doses for prospectively gated CTCA are an order of magnitude lower than retrospectively gated scans. Optimisation of cardiac protocols is expected to show further dose reduction.
In light of the proposal from the International Commission on Radiological Protection for a lowered eye dose limit, now adopted by a European Union Council Directive, lead glasses may be required for some staff in interventional radiology to ensure that occupational exposure is as low as reasonably practicable. To investigate the lens protection offered from various models of lead glasses exposed to X-rays coming from a source to the left and below, calibrated radiochromic film was positioned in the lens area of a head phantom. When the source-to-eye angles were large, the dose reduction factors (the ratio of eye dose without protection to dose with protection) to the right lens area were much lower than to the left lens area, particularly with smaller-lensed glasses, due to gaps in protection between the face and the glasses. The results of this study reiterate the importance of employers providing eyewear based on the morphology of, and fit to, individual workers' faces.
A practical method for skin dose estimation for interventional cardiology patients has been developed to inform pre-procedure planning and post-procedure patient management. Absorbed dose to the patient skin for certain interventional radiology procedures can exceed thresholds for deterministic skin injury, requiring documentation within the patient notes and appropriate patient follow-up. The primary objective was to reduce uncertainty associated with current methods, particularly surrounding field overlap. This was achieved by considering rectangular field geometry incident on a spherical patient model in a polar coordinate system. The angular size of each field was quantified at surface of the sphere, i.e. the skin surface. Computer-assisted design software enabled the modelling of a sufficient dataset that was subsequently validated with radiochromic film. Modelled overlap was found to agree with overlap measured using film to within 2.2° ± 2.0°, showing that the overall error associated with the model was < 1 %. Mathematical comparison against exposure data extracted from procedural Digital Imaging and Communication in Medicine files was used to generate a graphical skin dose map, demonstrating the dose distribution over a sphere centred at the interventional reference point. Dosimetric accuracy of the software was measured as between 3.5 and 17 % for different variables.
The use of mobile head computed tomography (CT) equipment in intensive care is of benefit to unstable patients with brain injury. However, ionising radiation in a ward environment presents difficulties due to the necessity to restrict the exposure to staff and members of the public according to regulation 8(1-2) of the Ionising Radiation Regulations 1999. The methodology for enabling the use of a mobile head CT unit in an open ward area is discussed and a practical solution given. This required the reduction in scatter doses through the installation of extra internal and external shielding, and a further reduction in annual scatter dose by restricting the use of the equipment based on a simulation of the annual ward workload.
Organ Dose Modulation or ODM (GE Healthcare, Milwaukee, WI) was evaluated to characterize changes in , image noise, effective dose, and organ dose saving to patients. Three separate investigations were completed: a tube current modulation phantom was scanned with and without ODM, a phantom was scanned with ODM, and Monte Carlo simulations were performed. ODM was found to reduce the by approximately 20% whilst increasing the noise by approximately 14%. This was reflected in the dose distribution, where the anterior peripheral dose was reduced by approximately 40% whilst the identical posterior dose remained largely unaffected. Enabling ODM for the entire scan would reduce the effective dose by approximately 24%; however, this saving reduces to 5% if the images are matched for . These savings mostly originated from reductions in dose to the stomach, breasts, colon, bladder, and liver. ODM has the effect of a global reduction in with an associated increase in image noise. The benefit of ODM was found to be reduced when the dose‐saving contribution from the reduced was removed. Given that there is a higher contribution to effective dose throughout the body from the anterior projections, consideration should be given to applying ODM throughout. PACS number(s): 87.10.Rt, 87.53.Bn, 87.57.C‐, 87.57.Q‐
The General Certificate of Secondary Education (GCSE) was first examined in 1988. During the previous few years, there were an increasing number of Joint Olevel/CSE examinations developed which aimed to cover the whole ability-range. Ordinary level (O level) was introduced in the early 1960s and was the only leaving examination at 16+. However, it was geared only towards the higher-ability school pupil: until the raising of the school leaving age in the early 1970s it was felt that there was no need for an external examination for children who left school at 15. After ROSLA (the raising of the school leaving age) there was an increasing need for some kind of leaving examination for the lower 70 per cent of children for whom the Olevel examination was not considered suitable. Therefore, in 1965, the Certificate of Secondary Education (CSE) was introduced. From then, until the mid-1980s, the two examinations ran side by side. CSE never gained the educational kudos enjoyed by the O-level examination. It was possible to double-enter, but teachers always had the problem of which was the best examination for a particular candidate; although a grade 1 at CSE was considered the equivalent of a pass at Ordinary level, there was always the suggestion that one was an easier route than the other. For this reason Joint O-level/CSE examinations were introduced by some examination boards. There was also the fact that schools had a choice of which of the examination boards, all of which with the exception of the Associated Examining Board (AEB) were controlled by the universities, they could choose to enter. The CSE examinations were run by regional examination boards, which meant that schools had no choice for their CSE candidates.
To accurately compare the radiation dose between prospectively gated cardiac multidetector CT (with and without iterative reconstruction) and diagnostic invasive coronary angiography using the latest International Commission on Radiological Protection 103 (ICRP) tissue weightings.
Design, setting and patients
A retrospective analysis of consecutive patients presenting to a university teaching hospital for investigation of coronary artery disease. Radiation doses for each technique were calculated using computational Monte Carlo modelling of a standard Cristy phantom rather than the application of previously published conversion factors. While these have frequently been used in other studies, they are based on out-dated ICRP tissue weightings (ICRP 60) and are for the whole chest rather than for structures irradiated in cardiac imaging. In order to allow a comparison, doses were calculated and expressed in terms of effective dose in millisieverts (mSv).
Results
From a population presenting for angiography within a clinical service, the median radiation dose from cardiac CT with standard filtered back-projection (84 patients, 5.4 mSv) was comparable with the dose from invasive diagnostic coronary angiography (94 patients, 6.3 mSv). The dose for cardiac CT using iterative reconstruction was significantly lower (39 patients, 2.5 mSv).
Conclusion
The median effective dose from cardiac CT with standard filtered back-projection was comparable with the effective dose from invasive coronary angiography, even with application of the most contemporary ICRP tissue weightings and use of cardiac specific volumes. Cardiac CT scanning incorporating iterative reconstruction resulted in a significant reduction in the effective dose.
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