Computer model indicates optimal shielding can reduce operator radiation doses close to “background” levels

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“With effective use of apron and ceiling and table shields, operator [radiation] doses can be reduced to the equivalent of one to two days of natural background radiation,” investigators write in the conclusion of a recently published study. 

Richard W Harbron (Royal Victoria Infirmary, Newcastle upon Tyne, UK) and colleagues—including senior author Bijan Modarai (King’s College London and Guy’s and St Thomas’ NHS Foundation Trust, London, UK)—recently shared this finding in a European Journal of Vascular and Endovascular Surgery (EJVES) Editor’s Choice paper. 

“The radiation doses received by staff members performing fluoroscopically guided interventional procedures are potentially high, raising concerns of increased risk of cancer and non-cancer effects such as cataracts,” Harbron et al outline in their introduction. They continue by noting that endovascular aneurysm repair (EVAR) procedures “are associated with especially high doses to both staff and patients, due to the procedural complexity and the thickness and density of the abdominal region”. 

It was the investigators’ objective in the present study to estimate operator organ radiation doses from fluoroscopically guided infrarenal EVAR procedures, using detailed exposure information contained in radiation dose structured reports.  

Harbron and colleagues share in their methods section that they calculated conversion factors relating to kerma area product (PKA) to primary operator organ doses using Monte Carlo methods for 91 beam angles and seven X-ray spectra typical of clinical practice. The investigators wrote a computer programme that was designed to select the appropriate conversion factor for each exposure listed in a structured report and multiplied it by the respective PKA, and detail that this system was used to estimate operator doses for 81 EVAR procedures for which structured reports were available. Harbron and colleagues state that they also investigated the impact of shielding scenarios and variations in operator positions. 

Writing in EJVES, the authors report that the median estimated effective dose without shielding was 113μSv (interquartile range [IQR] 71–252μSv) and specify that the highest median organ doses were for the colon (154μSv, IQR 81–343μSv) and stomach (133μSv, IQR 76–307μSv). They note that these dose estimates represent all exposures, including fluoroscopy and non-fluoroscopic digital acquisitions.  

The authors continue that, with minimal shielding provided by 0.25mm of lead (Pb) covering the torso and upper legs, the effective dose was reduced by a factor of around six, and that—with additional shielding from ceiling and table shields—a 25- to 50-fold reduction in dose is achievable. Finally, they share that estimated doses were highest where the primary beam was pointed directly away from the operator.  

In this discussion of their findings, Harbron et al stress that their results “need to be interpreted in terms of typical yearly caseloads”. To this point, they reference surgeon-specific clinical outcome data collected by the National Vascular Registry for 533 vascular surgeons in the UK. They specify that the latest available data, covering the period 2017–2019, “suggest that the median number of infrarenal aortic aneurysm repairs performed by a surgeon as primary operator was 18”. However, they also note that the range in number of procedures performed by a single surgeon was 1–95 “due to subspecialisation and centralisation”. They add that operators who perform “more complex, longer” fenestrated and branched EVAR procedures are exposed to even greater levels of radiation. “High-volume specialists may perform over 100 of these procedures on top of their annual workload of 20–30 infrarenal EVARs,” they write. Harbron and colleagues also highlight that it is also possible some operators may be genetically more susceptible to the effects of radiation exposure. 

In the discussion of their findings, the investigators mention that the procedures described in their study were all performed in a hybrid vascular suite with a fixed imaging system. They note that previous studies have shown these fixed systems may be associated with higher patient and occupational radiation exposures than a traditional C arm. However, they stress that this effect “may be offset by reducing operator time and advanced radiation reducing technologies such as fusion imaging”.  

The authors address a number of errors and uncertainties in their research. For example, they write: “If beam angle and X-ray energy can be accounted for in dose estimation, the largest source of uncertainty is operator position, which could easily range from -50% to +100%. The relationship between operator position and dose cannot be modelled by a simple application of the inverse square law because of the extended and non-isotropic nature of the scattering source.” As a result of this, they stress that their results “should be regarded as applicable only to the primary operator standing at the femoral access site”. 

Considering what their paper adds to the literature, the authors write that it “improves estimates of the radiation doses to primary operators during fluoroscopically guided aneurysm repair by taking into account beam angle and X-ray-specific information for each individual exposure during the procedure”. They anticipate that their study “will help operators ensure their exposure is kept as low as reasonably achievable and will raise awareness of dose reduction strategies”. 


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