C-arm angulation increases radiation exposure to operators during complex EVAR

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Endovascular specialists should be aware that radiation exposure to the operator’s head increases with angulation of the C-arm to the left anterior oblique position during repair of thoracoabdominal aneurysms. Physicians should, therefore, limit this manoeuvre, according to a new study presented at the European Society for Vascular Surgery (ESVS) Annual Meeting.

The data were presented by Mostafa Albayati, Academic Department of Vascular Surgery, Guy’s and St Thomas’ NHS Foundation Trust/King’s College London, London, UK, and the study was awarded the best paper prize at the ESVS meeting (23–25 September, Stockholm, Sweden). The lead author of the study is Bijan Modarai, consultant vascular/endovascular surgeon and senior lecturer in Vascular Surgery.

“Reliance on endovascular techniques and increasing procedural complexity means that the vascular interventionalist is exposed to significant radiation doses, particularly to unprotected body parts. The International Commission on Radiation Protection has set what is known as safe limits for occupational exposure, but the true biological effects of any exposure, however low, are unknown,” said Albayati.

He explained that the effects of radiation can be divided into deterministic effects, which are thought to occur only above a threshold dose and can cause skin erythema, cataracts or infertility, and stochastic effects, those responsible for DNA damage or cancer, and that have a linear relationship and can occur at any dose. “There have been several alarming reports in the literature of left side brain tumours in interventionalists, raising doubts about these recommended safe limits and concerns about the true effects of radiation exposure to the head,” he said.

The aims of the study presented at the ESVS meeting were to directly measure head and body radiation exposure to the operating team during complex endovascular repair of thoracoabdominal aneurysms, and identify factors determining exposure.

Between October 2013 and July 2014, consecutive elective endovascular repair of thoracoabdominal aortic aneurysm procedures using branched and fenestrated grafts performed in a hybrid operating theatre in one centre were prospectively analysed.

The operating team was positioned to the right of the patient in all cases, with the primary operator standing closer to the X-ray beam. Body (over-lead and under-lead) and head doses were directly measured for the primary and assistant operators using electronic dosimeters. Fluoroscopy and digital subtraction angiography acquisition times, C-arm angulation, dose area product and operator height were recorded.

Seventeen cases were analysed (Crawford II [n=4], Crawford III [n=2], Crawford IV [n=11]) with a median operative time of 280 minutes (200–330). Median age was 76 years (71–81), median body mass index was 28kg/m2 (25–31), and 82% were male. Stent grafts incorporated branches only (n=4), fenestrations only (n=10) or a mixture of branches and fenestrations (n=3). A total of 21 branches and 37 fenestrations were cannulated and stented. All cases involved the renal arteries and the superior mesenteric artery, and eight cases included also the coeliac artery.

The median fluoroscopy time per procedure was 89.1 minutes, the digital subtraction angiography time was 76.1 seconds and the median patient dose area product was 172.2Gy.cm2. There was no significant difference between fenestrated and branched procedures with regards to operating time, fluoroscopy time, total digital subtraction angiography time and patient dose area product.

Albayati noted that, although it was not part of the original study, the team compared the dose area product measurements collected in the study to historical measurement from when the same type of procedure was performed in the interventional radiology room. “The comparison showed that there was a clear difference between the two environments with the hybrid room being associated with significantly lower dose area product exposure than the interventional radiology room, and this was despite a longer procedural time which is likely related to the more complex cases that we have acquired over time,” he said.

The results of the study demonstrated that head dose was significantly higher in the primary operator compared with assistant operator (median 54 [24–130] μSv vs. 15 [7–43] μSv, respectively; p=0.022) as was over-lead body dose (median 80 [37–163] μSv vs. 32 [6–48] μSv, respectively; p=0.014). The corresponding under-lead (“total body effective”) doses were similar between operators (p=0.222).

Using simple and multiple linear regression model analyses, the investigators showed that primary operator height (r2= -0.649; p=0.042), digital subtraction angiography acquisition time in left anterior oblique position (r2=0.629; p<0.001) and degree of left anterior oblique angulation (r2=0.648; p<0.001) were independent predictors of greater primary operator head dose.

Albayati stated that there was a clear direct correlation between digital subtraction angiography time in left anterior oblique position and head dose, between the degree of left anterior oblique position angulation and head dose (the steeper angulations being associated with greater head dose), and also a clear inverse relationship between primary operator height and head dose, with the shortest operator being exposed to significantly higher doses of head radiation.

He commented: “This is the first study to directly measure radiation exposure to the head in the endovascular operating environment. Although the effective body radiation exposure is reassuringly low, there is a significantly higher exposure to the head, which is inversely related to operator height and increases with C-arm left anterior oblique position angulation.” He added, “The head is an unprotected area, and the deleterious effects of exposure to this area are not fully understood. Operators should be cognisant of head exposure increasing with angulation of the C-arm and limit this manoeuvre. In addition to measuring radiation dose, perhaps we should, therefore, study also the end effects of this exposure using biological correlates.” 

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