Radiation exposure during endovascular aneurysm repair.

BACKGROUND: Endovascular stent-grafting is an established option for the repair of abdominal aortic aneurysm (AAA) that can involve prolonged manipulation under radiological control. The aim was to determine the average radiation exposure sustained during endovascular aneurysm repair (EVAR) and the first year of postoperative surveillance. METHODS: Prospective radiation dose data were recorded and used to calculate dose area product (DAP) values for 96 patients undergoing EVAR. The DAP data were then used to determine the entrance skin dose (ESD), an indicator of potential skin damage, and the effective dose, an indicator of long-term cancer risk, for each patient. RESULTS: The median ESD during EVAR was 0.85 (interquartile range 0.51-3.74) Gy. The threshold for possible radiation-induced skin damage of 2 Gy was exceeded in 29 per cent of procedures. The effective dose of radiation in the first year following EVAR was 79 mSv. CONCLUSION: Radiation doses administered during EVAR were higher than previously thought, with a potential risk of radiation-induced skin damage and later malignancy.

An investigation into patient and staff doses from X-ray angiography during coronary interventional procedures.

Radiation doses to patients from interventional coronary X-ray procedures are relatively high when compared with conventional radiographic procedures. These high patient doses can translate into high staff doses owing to scattered radiation. This study investigates patient doses by means of dose-area product (DAP) meters installed in six rooms in two hospitals. DAP measurements in each room ranged from 28.0-39.3 Gy cm2 for coronary angiography and from 61.3-92.8 Gy cm2 for percutaneous transluminal coronary angioplasty, with the mean effective doses calculated to range between 5.1-6.6 mSv and 11.2-17.0 mSv, respectively. These values are comparable with those found in recent literature. DAP measurements were found to correlate strongly (correlation coefficient of 79%) with patient weight. The non-uniform scatter radiation fields surrounding the irradiated area during coronary angiography were also investigated using a tissue equivalent phantom and an ionization chamber. Exposure rates of scattered radiation from digital acquisition were found to be around 16 times higher than those generated from fluoroscopy, and oblique-angled imaging led to greater amounts of scatter owing to the increase in related exposure factors. The distribution of scatter from oblique projections confirms that X-ray photons in the diagnostic energy range are preferentially scattered backwards, toward the X-ray tube. These concepts are a major consideration when training individuals working in the angiography suite in order to keep doses "as low as reasonably practicable".

16-detector multislice CT: dosimetry estimation by TLD measurement compared with Monte Carlo simulation.

Computer simulations are widely used to estimate effective doses from CT examinations. The raw data often used in their estimations were obtained some years ago and made certain assumptions regarding CT unit design. At that time multidetector CT units were unavailable. Changes in design will limit the accuracy of computer simulated dosimetry on these machines. We therefore estimated CT dose on a 16-detector unit directly using thermoluminescent dosemeters (TLDs) and an anthropomorphic phantom. We found that the dose measured directly was 18% higher than the computer simulated dosimetry, in keeping with the previously recognised underestimation by computer simulation techniques compared with TLD measurements.

Effect of multislice scanners on patient dose from routine CT examinations in East Anglia.

As part of the dose optimization process, the Ionising Radiation (Medical Exposure) Regulations 2000 include requirements relating to the assessment of patient dose, and the setting and subsequent review of diagnostic reference levels. In East Anglia, audits of effective dose in CT have been carried out in 1996, 1999 and 2002. In the 2002 audit, nine of the 14 scanners assessed had been replaced since the previous audit. Eight of the new scanners were multislice scanners, acquiring up to 16 slices in a single rotation. The objective of the 2002 audit was to investigate the effect of the introduction of these multislice scanners on patient doses from routine CT examinations. Exposure parameters were collected for 10 different types of routine CT examination. In excess of 550 sets of patient data were obtained. For each of these, effective doses were calculated using the results of Monte Carlo simulations published by the National Radiological Protection Board. Averaged across all 10 examinations, regional mean effective doses are 34% higher than in 1999. The multislice scanners in the region give, on average, 35% more effective dose than the single-slice scanners. The effect of collimation in multislice scanners makes these effective dose differences most notable for examinations that use narrow slice widths. Further optimization of exposures on multislice scanners has the potential to reduce the differences observed between single-slice and multislice doses. However, when taken in combination with the increased use of CT in many hospitals, the effective dose increases observed are likely to result in a significant increase in the already substantial collective radiation dose from CT.

Is it safe to work with iodine-131 if you are pregnant? A risk assessment for nuclear medicine staff involved with cleaning and decontamination.

In the UK, Regulation 8(5) of the Ionising Radiation Regulations 1999 (In: Work with ionising radiation. London: HSE Books, 2000) requires employers to ensure that the dose to the foetus of a pregnant worker is unlikely to exceed 1 mSv. Risk assessments are required which are capable of predicting the total foetal dose. Work involving 131I is a particular problem. Foetal dose coefficients from the maternal intake of 131I for all stages of pregnancy have been published (Phipps AW, Smith TJ, Fell TP, Harrison JD. Doses to the embryo/fetus and neonate from intake of radionuclides by the mother. NRPB contract research report 397/2001. Didcot, Oxon.: National Radiological Protection Board (NRPB), 2001. Available on website www.hse.gov.uk/research/crr_pdf/2001/crr01397.pdf), and range from 0.08 microSv x kBq(-1) at conception to 55 microSv x kBq(-1) at week 35. This paper examines one aspect of work in a nuclear medicine department in which the source of 131I is uncontrolled to determine whether the risk assessment indicates that restrictions should apply to a pregnant member of staff. Following in-patient treatment with 131I, rooms are checked and decontaminated before being decontrolled. Cleaning staff were monitored immediately after the cleaning process with hand-held detectors and by whole-body monitoring. Total body contamination ranged up to 3.2 kBq; after a change of clothing, the maximum remaining activity was 0.68 kBq. Acquired contamination correlated with the total activity administered to the patient. Hand-held monitoring rarely detected contamination. Whole-body monitoring indicated that the levels of contamination encountered could lead to a dose limit for the foetus being exceeded. These levels are very difficult to detect with hand-held monitoring. The conclusion to be drawn is that pregnant staff should be excluded from situations in which accidents could arise, or where the source of 131I is uncontrolled or unpredictable.

Retinoid signalling acts during the gastrula stages to promote primary neurogenesis.

Retinoid signalling has been manipulated at different developmental stages to identify a critical period in the gastrula embryo for retinoid-dependent primary neurone formation. The expression of retinoid receptor RARalpha2 in the posterior neuroectoderm of the gastrula embryo is therefore consistent with a role in primary neurogenesis. In addition we show that the expression of neurogenin-1 and XDelta-1, two genes that contribute to the determination of primary neurone cell-fate in the gastrula embryo, respond to retinoid signalling. These results indicate that retinoid signalling is required for an early step in the process of primary neurogenesis. When retinoid signalling is increased, the number of primary neurones increases, but the phenotype is not the same as the neurogenic phenotype that follows the overexpression of a dominant negative form of XDelta-1. Whereas increased retinoid signalling expands the width of primary neurone stripes, dominant negative XDelta-1 increases the density of primary neurones within the stripes. When retinoid signalling is increased and the primary neurone stripes expand, the expression domain of a floorplate marker contracts. Conversely, when retinoid signalling is inhibited, the expression patterns of floorplate markers widen. These results indicate that retinoid signalling acts at an early stage in primary neural development when the fates of different regions of the neuroectoderm are being determined.

The control of Xenopus embryonic primary neurogenesis is mediated by retinoid signalling in the neurectoderm.

In Xenopus, the primary neurons form in three domains either side of the midline in the posterior neurectoderm. At the late neurula stage there are approximately 120 primary sensory neurons on each side of the embryo. Co-injecting synthetic mRNA encoding retinoic acid receptor alpha (NR1B1) and retinoid X receptor beta (NR2B2) results in an increase in the number of primary neurons and this is further enhanced by the addition of retinoic acid indicating that elevated retinoid signalling promotes an increase in the number of cells undergoing primary neurogenesis. However, primary neurogenesis remains confined to the three domains that normally give rise to primary neurons indicating that not all regions of the neurectoderm respond equivalently to elevated retinoid signalling. The inhibition of retinoid signalling with a dominant negative retinoid receptor or treatment with citral, an inhibitor of retinoid metabolism, inhibits the formation of primary neurons. However, the lateral extent of the neurectoderm does not differ following these experimental manipulations suggesting that changes in primary neuron cell number, in response to changes in retinoid signalling, cannot be accounted for by significant gains or losses of neurectoderm. In addition, two lines of evidence are presented to suggest that retinoid signalling affects primary neurogenesis by acting directly on the neurectoderm. First, animal caps neuralized by noggin undergo primary neurogenesis in response to retinoid signalling and second primary neurogenesis is elevated in neural conjugates in which the ectodermal, but not the mesodermal, component has been co-injected with RAR/RXR mRNA.

Expression of the Lewis group carbohydrate antigens during Xenopus development.

We have examined the pattern of expression of the Lewis group carbohydrate antigens during the development of African toad Xenopus laevis. One of these antigens, Lewis x (Le(x), also known as SSEA-1), was previously shown to be involved in cell-cell adhesion in early mouse embryos and teratocarcinoma stem cells. Recently another member of these antigens, sialyl-Le(x), was found to be one of the major ligands for the selectin family of cell-cell adhesion molecules. In order to study the role of carbohydrate-mediated cell adhesion during Xenopus development, we first studied the expression pattern of the Le(x). We found that Le(x)was not expressed in early embryos, started to be expressed at the tail bud stage in anterior regions of the body such as the cement gland or head skin, and was gradually showed more posterial expression at later stages. At tadpole stage, it was also expressed on specific cell bodies in brain, and in axon region in brain and neural retina. Antibodies against Le(x)blocked neurite outgrowth in the explant culture of tadpole brain. One of the candidates for Le(x)carrier protein in the tadpole brain is a 200 kDa glycoprotein detected by Western blotting. In adult tissues, it was expressed in brain, testis, and gut, but not in kidney, lung, spleen, ovary, or muscle. We also examined the expression patterns of other Lewis group antigens. Among them, sialyl-Le(x)was expressed on endothelial cells and on leukocytes, suggesting the possibility that it functions as a ligand for selectin in Xenopus.

The expression of XIF3 in undifferentiated anterior neuroectoderm, but not in primary neurons, is induced by the neuralizing agent noggin.

The gene XIF3 encodes a neural-specific type-III intermediate filament protein whose expression in the embryo precedes that of the neurofilaments by several hours. We now show, by in situ hybridization, that it is expressed at the neurula stage in primary neurons and, to a lesser extent, in undifferentiated anterior neuroectoderm. At the swimming tadpole stage, strong expression is restricted to the midbrain-hindbrain boundary, even-numbered rhombomeres of the hindbrain and the Vth and VIIth cranial ganglia. XIF3 gene expression can be induced in ectodermal cells (animal caps) derived from blastula when grown to the neurula stage in the presence of the neuralizing agent noggin. In agreement with the proposed ability of noggin to neuralize, but not to promote neuronal differentiation, we find that the pattern of noggin-inducible XIF3 expression in animal caps is consistent with expression in undifferentiated anterior neuroectoderm but not in primary neurons.

Retinoid receptors promote primary neurogenesis in Xenopus.

Retinoid receptors, which are members of the nuclear hormone receptor superfamily, act as ligand-dependent transcription factors. They mediate the effects of retinoic acid primarily as heterodimers of retinoic acid receptors (RARs) and retinoid X receptors (RXRs). To analyse their function, xRXR beta synthetic mRNA was injected into Xenopus embryos in combination with normal and mutated xRAR alpha transcripts. Two informative phenotypes are reported here. Firstly, over-expression of xRXR beta with xRAR alpha results in the formation of ectopic primary neurons. Secondly, blocking retinoid signalling with a mutated xRAR alpha results in a lack of primary neurons. These two phenotypes, from contra-acting manipulations, indicate a role for retinoid signalling during neurogenesis.

CT standard protocols are of limited value in assessing actual patient dose.

In the last 10 years the use of computed tomography in radiodiagnosis has increased markedly and CT scanners are now present in most district general hospitals. Modern CT scanners are versatile in their operation and offer the operator a wide choice in exposure parameters which affect the doses received by the patients. As CT is a major contributor to medical radiation doses, the National Radiological Protection Board (NRPB) recommends that an estimate of typical patient dose should be made for commonly used local scanning protocols. A survey has been undertaken in the Anglia and Oxford region covering 12 CT scanners. Common procedures were chosen, concentrating on those most frequently carried out and giving higher effective doses. These included routine heads, routine chests, high resolution chests and abdomen/pelvis examinations. Questionnaires were sent out to each CT centre to collect data on standard protocols and to record the procedure used for five actual patients for each examination type thus enabling a comparison of the two methodologies. This study has shown that many examinations are tailored to the individual patient size and clinical indications, particularly in the chest/abdomen/pelvis. Thus, assessing doses based on collecting standard protocols may not give a true indication of the effective doses being received by particular patients.

Overexpression of cadherins and underexpression of beta-catenin inhibit dorsal mesoderm induction in early Xenopus embryos.

The cadherin-catenin complex has an important role in cell-cell adhesion and may also function in signaling pathways. We report that overexpression of three cadherin types in Xenopus embryos causes them to develop with reduced dorsal axial structures. The same phenotype is produced in embryos that have been depleted of maternal beta-catenin protein by an antisense oligodeoxynucleotide complementary to beta-catenin mRNA. They show an inhibition in the expression of dorsal mesodermal markers MyoD and goosecoid, but not of ventral and general mesodermal markers. They lack notochords, somites, and neural tubes and are defective in dorsal mesodermal signaling in Nieuwkoop assays. The phenotype can be rescued by the injection of beta-catenin mRNA and not by the injection of Xwnt-8 mRNA. These results show that beta-catenin has an important role in dorsal mesoderm induction. They directly demonstrate the activity of a maternal mRNA in axis specification.

A functional test for maternally inherited cadherin in Xenopus shows its importance in cell adhesion at the blastula stage.

We report here on the consequences of reducing the expression of EP-cadherin at the earliest stages of Xenopus development. Injection of oligodeoxynucleotides antisense to maternal EP-cadherin mRNA into full-grown oocytes reduced the mRNA level in oocytes, and the protein level in blastulae. Adhesion between blastomeres was significantly reduced, as seen in whole embryos, and in assays of the ability of blastomeres to reaggregate in culture. This effect was especially conspicuous in the inner cells of the blastula and included the disruption of the blastocoel. The severity of the EP-cadherin mRNA depletion and of the disaggregation phenotype was dose dependent. This phenotype was rescued by the injection into EP-cadherin mRNA-depleted oocytes of the mRNA coding for a related cadherin, E-cadherin, that is normally expressed at the gastrula stage in the embryonic ectoderm.

Radiation exposure to the hands of orthopaedic surgeons during procedures under fluoroscopic X-ray control.

The hands of the surgeon are most likely to be directly exposed to ionizing radiation during fluoroscopic screening in the orthopaedic theatre. There is however little information available on the level of exposure to radiation during the normal working pattern of individual surgeons. The purpose of this study was to directly measure the radiation exposure to the hands during fluoroscopic screening in a series of consecutive cases over a month in order to establish whether these staff need to be designated classified persons, and if not, whether they need to be routinely monitored. Extremity monitoring was carried out using thermoluminescent dosimeters. The dosimeter was secured to the operating surgeon's dominant index finger. 44 procedures were carried out by nine different surgeons. The total radiation dose received per surgeon ranged from 48-2329 microSv. In 80% of procedures the dose of radiation to the surgeon's hand was less than 100 microSv. The extrapolated annual dose, even for the surgeon with the highest radiation exposure, was well below the annual dose limit for extremities of 500 mSv per year recommended by the International Commission on Radiological Protection, and embodied in the Ionizing Radiations Regulations 1985. Despite the relatively low doses of radiation received by surgeons in this study, occupational exposure to all personnel should be kept to the lowest practicable levels, and a review of procedures, including dose measurements, from time to time is advised.