Radiation Awareness for Endovascular Abdominal Aortic Aneurysm Repair in the Hybrid Operating Room. An Instant Patient Risk Chart for Daily Practice

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Abstract

Purpose: To determine which patient and C-arm characteristics are the strongest predictors of intraoperative patient radiation dose rates (DRs) during endovascular aneurysm repair (EVAR) procedures and create a patient risk chart. Methods: A retrospective analysis was performed of 74 EVAR procedures, including 16,889 X-ray runs using fixed C-arm imaging equipment. Four multivariate log-linear mixed models (with patient as a random effect) were constructed. Mean air kerma DR (DRAK, mGy/s) and the mean dose area product DR (DRDAP, mGycm2/s) were the outcome variables utilized for fluoroscopy as differentiated from digital subtraction angiography (DSA). These models were used to predict the maximum radiation duration allowed before a 2-Gy skin threshold (for DRAK) or a 500-Gycm2 threshold (for DRDAP) was reached. Results: The strongest predictor of DRAK and DRDAP for fluoroscopy imaging was the radiation protocol, with an increase of 200% when changing from “low” to “medium” and 410% from “low” to “normal.” The strongest predictors of DRAK and DRDAP for DSA were C-arm angulation, with an increase of 47% per 30° of angulation, and body mass index (BMI), with an increase of 58% for every 5-point increase in BMI. Based on these models, a patient with a BMI of 30 kg/m2, combined with 45° of rotation and a field size of 800 cm2 in the medium fluoroscopy protocol has a predicted DRAK of 0.39 mGy/s (or 85.5 minutes until the 2-Gy skin threshold is reached). While using comparable settings but switching the acquisition to a DSA with a “2 frames per second” protocol, the predicted DRAK will be 6.6 mGy/s (or 5.0 minutes until the 2-Gy threshold is reached). Conclusion: X-ray radiation DRs are constantly fluctuating during and between patients based on BMI, the protocols, C-arm position, and the image acquisitions that are used. An instant patient risk chart visualizes these radiation dose fluctuations and provides an overview of the expected duration of X-ray radiation, which can be used to predict when follow-up dose thresholds are reached during abdominal endovascular procedures.

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