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Radial Cradle® significantly decreases scatter radiation cloud by up to -51% (above) and 1st and 2nd operator radiation exposure by up to -79% (below), compared to arm boards during simulated catheter lab cine acquisition using a whole-body phantom.
Background
Minimising scatter radiation is important. Personal protection equipment (PPE) in the form of lead shielding is provided by most cath lab vendors, but conflict with other equipment e.g. arm boards (AB) may limit their effective deployment. Radial Cradle (RC) is a wearable patient arm support that removes the need for an arm board, allowing for the table mounted lead skirt to be deployed fully and ceiling mounted screens to be positioned more medially. We sought to investigate whether this would reduce scatter radiation, particularly to 1st and 2nd operators standing table side when the source was closest to the physician.
Methods
We compared the scatter radiation using AB and RC, measured by hand-held Raysafe dosimeter (nano Gray/ second – nG/s) in two gantry projections, (left anterior oblique (LAO) 30° and anteroposterior (AP) cranial 30°) using a whole-body anthropomorphic Kyoto phantom. All imaging parameters were constant and the available PPE was deployed. We measured scatter dose rate during acquisition (15fps) at 180cm, 120cm and 60cm height and 15° intervals, 100cm from the isocenter, as well as 1st and 2nd operator doses at 10cm intervals from head (180cm) to leg (70cm) on the left (L), midline (M) and right (R).
Results
Scatter cloud analysis confirmed that dose decreased as height increased (AB LAO 30 nG/s (SD) 60cm: 55 (30), vs. 120cm: 42 (24), vs. 180cm: 23 (15), p<0.0001) and was lower in the operator quadrant where PPE was deployed (AB LAO 30 nG/s (SD) 0-75°: 20 (23) vs. 90-345°: 46 (25), p<0.0002, lower panel). Scatter cloud nG/s 0-75° in LAO 30 using RC was 13 (20) vs. 20 (23), -35% (p=0.12) and in AP cranial was 9 (14) vs. 17 (21), -51% (p=0.004, lower panel) but was also lower 90-345° in LAO 30 -18% lower and in AP cranial -27% lower, both <0.0001 where no PPE was deployed, lower panel.
Both first and second operator dose nG/s (SD) was significantly lower when RC was used (1st operator AP: 3 (2) vs. 14 (10) -79%, LAO 30: 4 (4) vs. 13(14) -71%; p<0.002 and p<0.001 respectively and 2nd operator AP: 3 (3) vs. 9 (6) -67%, LAO 30: 6 (7) vs. 15 (9) -57%; both p<0.0001, upper panel. This was due to better lead shield deployment with RC.
Conclusion
Radial Cradle significantly decreases scatter radiation and operator dose by enabling better PPE deployment in the cath lab.
Operator eye and thorax equivalent dose is significantly lower when the arm is positioned along side the leg (blue) rather than abducted externally on an arm board (red). From Sciahbasi A et al. Am Heart J 2017;5922: 1-177.
Radial access procedures are associated with a higher radiation dose than femoral procedures for both the patient and operator (1,2).
Some of this is attributed to longer fluoroscopy screening times due to a learning curve and also possibly the inherent awkwardness of a radial access procedure. Operator dose is influenced by operator position relative to the X-ray source. The inverse square law is a well-known principle in radiation protection – doubling the distance from the x-ray source quadruples the dose reduction. However, it is less well appreciated that operator position relative to the patients’ arm position and, in turn, the x-ray shielding is also important.
When the arm is abducted externally on an arm board for a radial procedure it is not always possible to achieve optimal x-ray shielding (table lead skirting cannot be erected from below the table and the transparent lead screens cannot be moved close to the midline).
Adducting the arm towards the midline – so that the access site is adjacent to the leg is a simple measure that can reduce operator DAP-normalised dose by an average of 40% (3). Sciahbasi et al. concluded that: “This measure is cost saving and effective and should be considered for all programs aimed to reduce radiation exposure in the catheterization laboratory”.
Radial Cradle® helps achieve an adducted arm position close to the leg, facilitating better radiation protection measures that have been shown to reduce operator radiation exposure (3,4).
Unpublished raw data, on file at Radial Cradle Ltd.
Radial access procedures are associated with higher first operator radiation doses which can be deleterious e.g. cataracts. Right radial access in particular results in higher eye doses due to suboptimal positioning of personal protection equipment (PPE) when the arm is abducted on arm boards. This can be corrected by moving the arm medially. Radial Cradle® passively supports the arm in a medial, ergonomic orientation enabling better PPE (table lead under-skirt deployment and lead Perspex screen more medial).
An initial study has been completed that sought to confirm if this device would lower first operator radiation doses.
Fifty consecutive right radial access percutaneous coronary interventions – PCI (26 using Radial Cradle® (RC) and 24 using arm board (AB)) had fluoroscopic and cine image guidance in standard views acquired at 15 frames per second in low dose mode using a Philips Azurion. PPE was positioned as per standard practice by the operator. Insta-dose badges provided by the same vendor were worn at the left collar of the first operator to provide first operator effective dose (uSv) per procedure. The normalised effective dose was calculated by dividing the effective dose by the dose area product (DAP – Gy.cm2) delivered to the patient. Historic average first operator effective and normalised dose for the preceding month (45 cases) using arm boards were also compared to account for any Hawthorn effect – a change in radiation awareness behaviour and operator dose as result of being observed.
Positioning the right arm medially using Radial Cradle® significantly reduced first operator mean effective and normalised effective doses when compared with arm boards (RC: 5.6 ± 12.5 vs. AB: 23.6 ± 34.8 uSv, p=0.004 and RC: 0.20 ± 0.39 vs. AB: 0.91 ± 1.71 uSv/Gy.cm2, p=0.007 respectively). This equated to an important 76.3% reduction in mean effective first operator dose and 78.3% reduction in mean normalised dose. The first operator Insta-dose recording was undetectable in 10/26 (38.5%) of PCI cases using Radial Cradle®. The table lead under-skirt PPE was deployed in 100% of Radial Cradle® cases but was obstructed by the use of the arm boards and remained undeployed in all arm board cases. The lead Perspex screen PPE was used in all cases.
Historic mean effective and normalised effective doses using arm boards were higher than arm board doses observed in the trial (30.4 vs. 23.6 uSv and 0.95 vs. 0.91uSv/Gy.cm2, respectively), confirming a modest dose lowering due to the Hawthorn effect.
Positioning the right arm medially using Radial Cradle® for right radial access PCIs significantly reduces first operator dose, by enabling optimal PPE positioning. Procedural dose awareness using Insta-dose also modestly reduces first operator dose, compared to historic controls.
Radial Cradle Ltd. is registered in England, company number 10539165.
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