Background Interventional procedures via radial technique have progressively increased due to improved patient comfort, lower complication rates and reduced mortality in some scenarios. One area of interest is radiation exposure and ways of minimising it. Most studies focus on patient radiation risk with conflicting results, but there is reasonable consensus for increased operator exposure from the radial technique. The aim of this study was to evaluate radiological exposure under controlled radial and femoral access simulation tests, mapping radiation paths and developing a radiological protection device for the transradial technique.
Methods and results Radiation exposure was simulated under controlled conditions for femoral and radial techniques using a pressurised ionisation chamber and water phantom. Different measurement points were defined according to standard positions to simulate radiation received by the operator in the gonads, thyroid and eyes at different angles during real procedures. The radial technique increased total exposure by 33% over the femoral technique. A protective device was developed and tested after radiation mapping. The protective device reduced cumulative radiation by 52% against the radial and 36% against the femoral technique.
Conclusions In our study, operator exposure to cumulative ionising radiation was higher from the radial technique and the protective device reduced radiation exposure levels in the radial and femoral techniques. These results provided the basis for a clinical trial design to better define the impact of the protection device and radiation exposure during real world practice using different interventional techniques.
- vascular access
- radial artery catheter
- radiation risk
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Interventional cardiology has, at its core, procedures using invasive vascular access. Of the strategies used, brachial dissection is of historical significance being the first technique used, and the current most frequent access route is the modified Seldinger Technique1 via femoral artery puncture. Materials and strategies that reduce vascular complications in invasive coronary procedures have recently been added to the toolbox, especially the radial technique, which is a potential alternative to the femoral technique.2
Some of the advantages of radial access are lower bleeding and vascular complication rates,3–5 with further reductions in hospitalisation6 and mortality in some higher risk patient subgroups,5 ,7 ,8 and it has increasingly been adopted all over the world,9 with possible consideration as the routine approach strategy of choice.9 ,10
Radiation risk and access route
There are two well-known general patterns of damage related to ionising radiation: the deterministic and stochastic effects. Deterministic effects cause cell death that is not compensated for by replacement or repair, with detectable tissue or organ damage. It is an all-or-nothing effect where there is a dose threshold below which the loss of cells is insufficient to cause detectable harm. Examples are dry skin desquamation and erythaema for doses between 3 and 5 Gy and necrosis over 50 Gy. There is also a time lag, with effects generally occurring after 3–4 weeks. Stochastic effects are caused by random cell damage where probability is proportional to received radiation dose without any threshold. Of these effects, the oncological risk11 is of concern as the latency period after exposure can be over 40 years,12 and ways to minimise radiation have been afforded increasing attention.13 ,14
A concern arising from this context where radial techniques benefit patient clinical outcome, is the increased potential for ionising radiation exposure,15 as it can become a technique limitation. On average, a coronary angiography and angioplasty correspond to patient radiation exposure levels of 300 and 1000 radiographs, respectively.16 Several randomised studies have examined differences between radial and femoral techniques related to this topic; most of their data infer higher fluoroscopy time, but without significance when compared to radiation dose absorbed by the patient derived from the access route.17 ,18 The literature is relatively scarce when focusing on operator exposure. However, there seems to be some consensus on higher exposure from radial access; though there is little standardisation of radiation impact assessment methods. Perhaps the main limitation of these studies is that most are of observational design and few were planned using dosimeters specifically dedicated to evaluating operator absorbed dose in accordance with access choice.19 ,20
The default optimal radiation protection set includes a radioprotection apron, a thyroid collar, lead goggles, a vinyl lead curtain in the lower region of the catheterisation table and a suspended moveable glass shield. Such a set is widely used and effective in protecting the operator from 95% of the radiation to which he or she is exposed.21
Additional devices have been developed to reduce operator exposure; these include radiation protection sheets22 and extensor tables23 with lower shields covered with lead sheets, which are generally successful, with levels of reduction up to 30%. However, their adoption is not widespread; this may be due to technical difficulties in their use. This opens up an area of research and development for new technologies to reduce interventionist ionising radiation exposure and even facilitate radial procedure performance.
The Transradial Intervention Table Protection (TRIPTable) device (patent required) is a polycarbonate support table anatomically-designed for the radial technique, facilitating puncturing, standardising sequential technique steps, providing material support and allowing radioprotection from a protective layer designed to block radiation without obstructing fluoroscopic images (figure 1).
The objective of this study is to analyse the differences in radiation from simulated femoral and radial routes, focusing on impact to the operator during interventional cardiology procedures, and aimed at developing radioprotective devices specifically for the radial technique.
Materials and methods
The study has been approved by Institutional Ethical Committee and written informed consent was obtained to take part in the study.
A radiological field test was performed in a catheterisation laboratory by simulating operator position using a fluoroscopy station (Philips Allura Xper FD20) in a 27″ field with standard below-and-above table protection apparatus (superior protection glass and curtain, the first angled at 45° and positioned to contact the lower skirt). Radiation levels were measured by an external independent company using a Victoreen 450P ionisation chamber pressurised to 6 atm, and a water phantom to simulate the human body. The acquisition sequence was performed according to five projections. A zero projection (cranial-caudal and zero lateral angulations) followed by angled projections at 30° to the four directions (cranial, caudal, left and right). The measuring points were grouped into three different simulations: radial position with standard support (Philips standard cath arm support NCVA097), and radial position with a TRIPTable device and femoral position. The femoral projection was defined by the operator in a working position 30 cm caudally distant from the radial position and 30 cm frontal distance from the table.
Each position (radial, femoral and TRIPTable) received three standardised points aiming at the eyes, thyroid and gonads (1.70, 1.30 and 0.80 m high, respectively). The X-ray tube default georeset position was set at 50 cm above ground and the table 40 cm from the tube. The flat panel was positioned 30 cm above the table. The controlled test predefined positions are shown in figure 2. Shield positioning diagrams are shown in figures 3 and 4.
There were differences between groups in level of radiation directed at the operator. Levels according to simulated technique are shown in figure 5 and table 1 (according different angulations) and by projection and measurement sites in figure 6.
Femoral radiation proportion was defined by the formula: (specified projection−femoral projection)/femoral projection×100; this can be seen in table 2. Total radiation exposure was 33% higher by radial technique than femoral technique. Cumulative exposure incidence was 52% lower than the radial technique and 36% lower than the femoral technique when the TRIPTable device was used.
In our study, the simulated radial technique exposed the operator to the highest cumulative dose of ionising radiation; the protective device reduced radiation exposure levels in the radial and femoral techniques. These results provide a basis for a clinical trial designed to better define the impact of operator radiation exposure during real world clinical practice.
TRIPTable trial design
Our study hypothesis is that using the radial access protective device TRIPTable is not inferior to the standard femoral technique, and is superior to the standard radial technique as a radioprotection strategy for the operator, in patients with acute coronary syndromes submitted to cardiac catheterisation. This is a prospective, 1:1:1 randomised, unicentric study comparing the femoral and radial techniques, with and without a TRIPTable device (NCT02200783). The primary endpoint will be assessed immediately after interventional procedure termination. The secondary and safety end points will be recorded after interventional procedure termination at time of hospital discharge. The possibility of bias derived from the Hawthorne effect is a major concern. Thus, a randomised historical cohort between radial and femoral techniques, with identical inclusion and exclusion criteria, will be the subject of a comparative analysis (ARISE study—NCT01653587).24
Primary outcome: accumulated operator radiation dose received during interventional cardiology procedures measured by thermoluminescent dosimeters.
Secondary outcomes: accumulated radiation dose received by each measured site (gonads, thyroid and eyes), operator radiation dose according to linear correlation for total dose area product, and procedure success rate, defined by performing the procedure without needing to cross between techniques.
Patients admitted are those with moderate to high risk acute coronary syndrome and scheduled for early invasive stratification strategy by coronary angiography followed by percutaneous coronary intervention (PCI), if applicable. Patients will be evaluated in terms of the feasibility of the radial and femoral access procedures. After evaluation, a patient meeting all inclusion criteria and no exclusion criteria may be included in study after signing the free and informed consent form.
Procedures will be performed according to current guidelines, including adjunctive antithrombotic and anticoagulant pharmacotherapy. Operators participating in the study should have performed at least 350 diagnostic or therapeutic procedures in the last year by transradial approach for radial experience qualification.10 Operators will be equipped with the full set of personal radiation protection in all procedures, including lead aprons, thyroid protective collar, lead goggles, and upper and lower table shields, all with at least 0.5 mm Pb equivalent protection.
Unstable angina with an indication for invasive stratification
Acute coronary syndrome without ST-segment elevation
Acute coronary syndrome with ST-segment elevation
Patient informed of the nature of the study and has signed the informed consent
Patient suitable for coronary angiography and coronary intervention either by radial or femoral access
Less than 18 years old
Chronic use of vitamin K antagonists, direct thrombin inhibitors, or factor Xa antagonists
Active bleeding or high risk of bleeding (severe hepatic insufficiency, active peptic ulcer disease, creatinine clearance <30 mL/min, platelet count <100 000 mm3)
Uncontrolled hypertension (persistent systolic blood pressure >180 mm Hg)
Previous coronary artery bypass graft surgery with the use of ≥1 graft
Patients not suitable for any of the specified vascular access routes
Concomitant severe disease with life expectancy less than 12 months
Medical, geographical or social conditions that impede participation in the study
Refusal or inability to understand and sign the informed consent form
The primary study hypothesis is that the use of the device is not inferior to the femoral technique in terms of operator radiation exposure and not inferior to the standard radial technique in terms of success rate and patient radiological exposure. The analysis was defined as for ‘intention to treat’, which means there is no need for the operator to change the dosimeter, whether the diagnostic procedure or angioplasty is completed, but only to record the type of procedure ultimately performed.
To balance procedure data and avoid additional technique biases (eg, short-duration vs long-duration procedures, projection angle, incorrect operator positioning), primary study outcome will be cumulative dose in each set of dosimeters. In prespecified secondary analysis we will also quantify the total radiation received at each specific operator site.
Sample size was estimated on the primary end point (total radiation received by the operator as measured cumulatively in all dosimeters: gonads, thyroid and eyes). Considering cumulative analysis of the primary outcome, sample size is calculated for the number of dosimeters required, rather than the number of procedures. Previous randomised prospective studies19 ,25 that have compared the radial and femoral techniques have shown an average increase in radiation received by the operator of 61.3% in PCI when using the transradial approach. Another study_ENREF_1818 evaluating chest radiation between radial and femoral approaches showed an average operator absorption of 20.9±13.8 mSv in the radial procedure and 15.3±10.4 mSv in the femoral procedure (p<0.001). To analyse a hostile scenario with a SD of 13.8 and 6.45 mSv difference, we calculated a 72 dosimeter sample (24 patients per group) for 80% power and 96 dosimeters per group for a 90% power with an α error of 0.05. As three dosimeters are being evaluated per patient, we estimate 32 subjects for each arm of the study. In order to facilitate comparison with an external database, we obtained a 99 subject sample.
Categorical variables will be expressed as frequency and percentage, and compared using the χ2 or Fisher exact tests. Continuous variables will be expressed as mean and SD, or median and IQR when appropriate, and compared with the Student t test. Linear regression will be used to estimate the relation between total radiation dose and operator-received radiation with the three different techniques. In all tests, the results will be considered significant when p value <0.05.
In our study, we found an increased radiation exposure level using radial technique compared to femoral technique. The TRIPTable device reduced operator-directed radiation exposure under controlled simulation conditions compared to both techniques. There are some limitations to the analysis. This is a single centre simulated study and requires external validation before further conclusions may be drawn. Additionally, in real world situations, multiple variables can influence the protection of the operator and may considerably interfere with radiological exposure.
Impact on daily practice
Our results suggest that there is increased operator radiation exposure with the radial technique compared to the femoral technique. A protective device could help to decrease this. The TRIPTable trial may help to better define the impact of radiation exposure during daily clinical practice.
Enrolment was initiated in July 2014 and, up to February 2015, 62 patients had been included. The inclusion phase is expected to last through the first half of 2015.
The authors wish to express their gratitude to Professor Paulo Craveiro of the physics and radiotherapy department (in memoriam), who was unrestrictedly helpful and offered invaluable assistance, support and guidance. The authors are deeply saddened by the passing of Professor Paulo Craveiro, a master of the radiation field, and as its discoverers, victim of its harmful effects. Without his knowlege this work would not be possible. Thank you very much Professor.
Contributors Professor Paulo Craveiro (in memoriam) initiated the study design and provided physics research expertise.
Competing interests None declared.
Patient consent Obtained.
Ethics approval Institutional Ethical Committee.
Provenance and peer review Not commissioned; internally peer reviewed.
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