Investigation of reference levels and radiation dose associated with abdominal EVAR (endovascular aneurysm repair) procedures across several European Centres

Lowest reported dose area product of 2.4 Gy∗cm2 for ultra-low-dose endovascular aortic aneurysm repair of a standard infrarenal aortic aneurysm

This is a report of successful treatment of an abdominal aortic aneurysm via standard endovascular aortic repair with an ultra-low dose (ULD) of 2.4 Gy∗cm2 using the latest imaging software in a hybrid operating room. To the best of our knowledge, no case has yet been reported achieving a successful outcome with such ULD values to date. The key factors to achieving an ULD regarding the dose area product comprise the right technology, procedural standardization, and team education and training. This case highlights the potential for reducing the radiation dose routinely for patients and staff alike, especially for operating room staff with daily radiation exposure.

National UK Survey of Radiation Doses During Endovascular Aortic Interventions

PURPOSE

Endovascular aortic repair (EAR) interventions, endovascular abdominal aortic repair (EVAR) and thoracic endovascular aortic repair (TEVAR), are associated with significant radiation exposures. We aimed to investigate the radiation doses from real-world practice and propose diagnostic reference level (DRL) for the UK.

MATERIALS AND METHODS

Radiation data and essential demographics were retrospectively collected from 24 vascular and interventional radiology centres in the UK for all patients undergoing EAR-standard EVAR or complex, branched/fenestrated (BEVAR/FEVAR), and TEVAR-between 2018 and 2021. The data set was further categorised according to X-ray unit type, either fixed or mobile. The proposed national DRL is the 75th percentile of the collective medians for procedure KAP (kerma area product), cumulative air kerma (CAK), fluoroscopy KAP and CAK.

RESULTS

Data from 3712 endovascular aortic procedures were collected, including 2062 cases were standard EVAR, 906 cases of BEVAR/FEVAR and 509 cases of TEVAR. The majority of endovascular procedures (3477/3712) were performed on fixed X-ray units. The proposed DRL for KAP was 162 Gy cm2, 175 Gy cm2 and 266 Gy cm2 for standard EVAR, TEVAR and BEVAR/FEVAR, respectively.

CONCLUSION

The development of DRLs is pertinent to EAR procedures as the first step to optimise the radiation risks to patients and staff while maintaining the highest patient care and paving the way for steps to reduce radiation exposures.

Cumulative Effective Dose During Fluoroscopically Guided Interventions (FGI): Analysis of More Than 5000 FGIs in a Single European Center

BACKGROUND

The number of fluoroscopically guided interventions (FGI) has increased significantly over time. However, little attention has been paid to possible stochastic radiation effects. The aim of this retrospective study was to investigate the number of patients who received cumulative effective doses over 100 mSv during FGI procedures.

MATERIAL AND METHODS

Five thousand five hundred and fifty four classified FGI procedures were included. Radiation dose data, retrieved from an in-house-dose-management system, was analysed. Effective doses and cumulative effective doses (CED) were calculated. Patients who received a CED > 100 mSv were identified. Radiology reports, patient age, imaging and clinical data of these patients were used to identify reasons for CED ≥ 100 mSv.

RESULTS

One Hundred and thirty two (41.1% female) of 3981 patients received a CED > 100 mSy, with a mean CED of 173.5 ± 84.5 mSv. Mean age at first intervention was 66.1 ± 11.7 years. 81 (61.4%) of 132 were older than 64 years, one patient was < 30 years. 110 patients received ≥ 100 mSv within one year (83.4%), through FGIs: EVAR, pelvic/mesenteric interventions (stent or embolization), hepatic interventions (chemoembolization, TIPSS), embolization of cerebral aneurysms or arterio-venous-malformations.

CONCLUSIONS

Substantial CED may occur in a small but not ignorable fraction of patients (~ 3%) undergoing FGIs. Approximately 2/3rd of patients may most likely not encounter radiation-related stochastic effects due to life-threatening diseases and age at first treatment > 65 years but 1/3rd may. Patients undergoing more than one FGI (77%) carry a higher risk of accumulating effective doses > 100 mSv. Remarkably, 23% received a mean CED 162.2 ± 72.3 mSv in a single procedure.

A neural network-enhanced methodology for the rapid establishment of local DRLs in interventional radiology: EVAR as a case example

PURPOSE

To develop a neural network-enhanced workflow for the automatic and rapid establishment/update of local diagnostic reference levels (DRLs) in interventional radiology (IR) using endovascular aneurysm repair (EVAR) procedures as a case example.

METHODS

Radiation dose reports were collected retrospectively for 46 consecutive EVAR procedures. These reports served as demonstrative data for the development of the proposed methodology. An algorithm was developed to receive multiple dose reports, automatically extract the kerma area product (KAP), air kerma (Ka,r), number of exposure images, and fluoroscopy time (FT) from each report and calculate the first, second, third quartiles as well as the maximum and minimum values of the extracted parameters. To extract the values of interest from the dose reports, Tesseract, an open-source optical character recognition (OCR) engine was employed. Furthermore, the accuracy and time efficiency of the proposed methodology were assessed. Specifically, the values extracted from the algorithm were compared with the ground truth values and the algorithm's processing time was compared with the respective time needed to manually extract and process the values of interest.

RESULTS

The OCR-based algorithm managed to correctly recognize 182 from the 184 target values, resulting in an accuracy of 99%. Moreover, the proposed pipeline reduced the processing time for the establishment of DRLs by 98%. DRL value for EVAR procedures, set as the third quartile of KAP was found to be 551 Gy*cm2.

CONCLUSION

An accurate and time-efficient workflow was developed for the establishment of local DRLs in interventional radiology.

Patient Radiation Doses in IR Procedures: The American College of Radiology Dose Index Registry-Fluoroscopy Pilot

PURPOSE

To update normative data on fluoroscopy dose indices in the United States for the first time since the Radiation Doses in Interventional Radiology study in the late 1990s.

MATERIALS AND METHODS

The Dose Index Registry-Fluoroscopy pilot study collected data from March 2018 through December 2019, with 50 fluoroscopes from 10 sites submitting data. Primary radiation dose indices including fluoroscopy time (FT), cumulative air kerma (Ka,r), and kerma area product (PKA) were collected for interventional radiology fluoroscopically guided interventional (FGI) procedures. Clinical facility procedure names were mapped to the American College of Radiology (ACR) common procedure lexicon. Distribution parameters including the 10th, 25th, 50th, 75th, 95th, and 99th percentiles were computed.

RESULTS

Dose indices were collected for 70,377 FGI procedures, with 50,501 ultimately eligible for analysis. Distribution parameters are reported for 100 ACR Common IDs. FT in minutes, Ka,r in mGy, and PKA in Gy-cm2 are reported in this study as (n; median) for select ACR Common IDs: inferior vena cava filter insertion (1,726; FT: 2.9; Ka,r: 55.8; PKA: 14.19); inferior vena cava filter removal (464; FT: 5.7; Ka,r: 178.6; PKA: 34.73); nephrostomy placement (2,037; FT: 4.1; Ka,r: 39.2; PKA: 6.61); percutaneous biliary drainage (952; FT: 12.4; Ka,r: 160.5; PKA: 21.32); gastrostomy placement (1,643; FT: 3.2; Ka,r: 29.1; PKA: 7.29); and transjugular intrahepatic portosystemic shunt placement (327; FT: 34.8; Ka,r: 813.0; PKA: 181.47).

CONCLUSIONS

The ACR DIR-Fluoro pilot has provided state-of-the-practice statistics for radiation dose indices from IR FGI procedures. These data can be used to prioritize procedures for radiation optimization, as demonstrated in this work.

A MODEL FOR EVALUATING THE USE OF IMAGING IN IMAGE-GUIDED INTERVENTIONAL PROCEDURES-POSSIBLE IMPLICATIONS ON OPTIMISATION OF RADIATION PROTECTION

The present study focuses on introducing the concept of optimisation and proposing a model, including evaluation of image quality, to be used in the clinical routines where image-guided intervention is being performed. The overall aim of the study was to develop a model for evaluating the use of imaging in X-ray-guided interventional procedures and its possible implications on optimisation of radiation protection. In the search for an adequate evaluation model, data from endovascular interventions of the aorta (EVAR procedures) were used. The procedure was schematically described in steps. Every imaging event was connected to the steps in the medical procedure and was also described with the purpose of the imaging event. Available technical, as well as procedural parameters, were studied and analysed. Data were collected from the X-ray equipment for 70 EVAR procedures and, out of these, 12 procedures were randomly selected to be recorded on video to understand the procedure better. It was possible to describe the EVAR procedures in a general way with explanations of the clinical purpose connected to each imaging event. Possible quality parameters of the procedure were identified for the imaging events (radiation dose, image quality). The model method still needs to be refined and will then be applied to clinical data and to other clinical procedures to test the validity.

KERMA-AREA PRODUCT, ENTRANCE SURFACE DOSE AND EFFECTIVE DOSE IN ABDOMINAL ENDOVASCULAR ANEURYSM REPAIR

This study aims to evaluate patient radiation dose during fluoroscopically guided endovascular aneurysm repair (EVAR) procedures. Fluoroscopy time (FT) and kerma-area product (KAP) were recorded from 87 patients that underwent EVAR procedures with a mobile C-arm fluoroscopy system. Effective dose (ED) and organs' doses were calculated utilising appropriate conversion coefficients based on the recorded KAP values. Entrance surface dose (ESD) was calculated based on KAP values and technical parameters. The mean FT was 22.7 min (range 6.4-76.8 min), resulting in a mean KAP of 36.6 Gy cm2 (range 2.0-167.8 Gy cm2), a mean ED of 6.2 mSv (range 0.3-28.5 mSv) and a mean ESD of 458 mGy (range 26-2098 mGy). The corresponding median values were 17.4 min, 25.6 Gy cm2, 4.4 mSv and 320 mGy. The threshold of 2 Gy for skin erythema was exceeded in two procedures for a focus-to-skin distance (FSD) of 40 cm and six procedures when an FSD of 30 cm was considered. The highest doses absorbed by the adrenals, kidneys, spleen and pancreas and ranged between 3.7 and 313.3 mGy (average 66.8 mGy), 3.3 and 285.1 mGy (average 60.8 mGy), 1.3 and 111.1 mGy (average 23.7 mGy), 1.1 and 92.1 mGy (average 19.6 mGy), respectively. A wide range of patient doses was reported in the literature. The radiation dose received by the patients was comparative or lower than most of the previously reported values. However, higher doses can be revealed due to the X-ray system's non-optimum use and extended FTs, mainly affected by complex clinical conditions, patients' body habitus and vascular surgeon experience. The large variation of patient doses highlights the potential to optimise the EVAR procedure by considering the balance between the radiation dose and the required image quality. Additional studies need to be conducted in increasing the vascular surgeons' awareness regarding patient dose and radiation protection issues during EVAR procedures.

Understanding the Basis of Radiation Protection for Endovascular Procedures: Occupational and Patients

Introduction

Some concepts of radiation protection are not well understood and must be refreshed periodically. The basic knowledge that a vascular surgeon must have about radiation protection for patients and staff is summarised.

Report

Diagnostic reference levels are a form of investigation into the medical exposure of patients during diagnostic and endovascular procedures that help to optimise them. Radiological quantities such as dose area product, also known as kerma area product and cumulative dose, are the most relevant to the patient. Equivalent dose, in mSv, determines the dose limits for staff. The effective dose (related to absorbed dose), also in mSv, represents the global risk of cancer and hereditary effects. For patient protection, the most important factors are fluoroscopy time, collimation, magnification, keeping the patient as near as possible to the image detector and as far as possible away from the tube, and trying to work in fluoroscope mode. Regarding occupational protection, distance, shielding, and dosimetry are the most important.

Discussion

With the increased use of endovascular procedures, radiation protection is an issue that has grown in importance. Radiation protection is based on three principles: justification; optimisation; and dose limits. Every action focused on reducing a patient's radiation dose will also reduce the dose to staff. Basic principles such as “the further away the better”, “always use a lead apron, thyroid protector, and lead glasses”, and “do not forget to wear personal dosimeters” must be remembered at all times.

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Radiation protection focuses on healthcare staff and patients.

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Diagnostic reference levels are essential in standard procedures.

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Operators should know their personal dose and radiation limits.

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Time, distance, and shielding are important.

A novel personalized dosimetry method for endovascular aneurysm repair (EVAR) procedures

OBJECTIVE

To estimate radiation doses for the primarily irradiated organs/tissues of patients subjected to standard endovascular aneurysm repair (EVAR) procedures using a novel personalized dosimetry method.

METHODS

Dosimetric and anthropometric data were collected prospectively for eight patients who underwent standard EVAR procedures. Patient-specific Monte Carlo simulations were performed to estimate organ/tissue doses from each of the fluoroscopic and digital subtraction angiography acquisitions involved in EVAR. Individual-specific cumulative absorbed doses were estimated for the skin, spinal bone marrow, heart, kidneys, liver, colon, bladder, pancreas, stomach, and spleen and compared to corresponding values estimated through a commercially available dosimetric software package that employs standardized phantoms.

RESULTS

The highest organ/tissue radiation doses from EVAR were found for the skin, spinal bone marrow, kidneys, and spleen as 192.4 mGy, 96.7 mGy, 72.9 mGy, and 33.6 mGy respectively, while the doses to the heart, liver, colon, bladder, pancreas, and stomach were 6.3 mGy, 14.4 mGy, 18.4 mGy, 14.8 mGy, 21.6 mGy, and 11.2 mGy respectively. Corresponding dose values using standardized phantoms were found to differ up to 151%.

CONCLUSION

Considerable radiation doses may be received by primarily exposed organs/tissues during standard EVAR. The specific size/anatomy of the patient and the variation in exposure parameters/beam angulation between different projections commonly involved in EVAR procedures should be taken into account if reliable organ dose data are to be derived.

KEY POINTS

• A novel patient-specific dosimetry method was utilized to estimate radiation doses to the primarily irradiated organs/tissues of patients subjected to standard endovascular aneurysm repair procedures. • The use of standardized mathematical anthropomorphic phantoms to derive organ dose from fluoroscopically guided procedures may result in considerable inaccuracies due to differences in the assumed organ position/volume/shape compared to patients.

Factors affecting radiation exposure in endovascular repair of abdominal aortic aneurysms: a pilot study

BACKGROUND

Radiation exposure during endovascular repair (EVAR) of abdominal aortic aneurysms (AAAs) is a potential issue. Several studies have identified factors affecting radiation exposure, although they are limited. The aim of this study was to identify independent factors affecting radiation exposure in patients with AAA undergoing standard EVAR.

METHODS

Forty-eight consecutive patients underwent elective EVAR for infrarenal AAA managed between April 2019 and April 2020. Fluoroscopy time (FT) and kerma area product (KAP) were the main outcome measures.

RESULTS

Median (interquartile range) FT and KAP values were 1018 (653-1619) s and 2.68 (2.08-3.81) mGy·m², respectively. C3 Excluder graft use and main body insertion site from the right femoral were associated with significantly lower FT. Coronary artery disease, endografts with two docking limbs, AAA diameter, neck angle and length, procedure duration, contrast amount, and hospitalization were associated with significantly higher FT. Neck angle was the single independent perioperative factor related to FT higher than the median value observed in the study (P=0.004, odds ratio: 1.073, 95% confidence interval: 1.023-1.126). The use of the C3 Excluder device was associated with lower KAP. AAA diameter, neck angle, procedure duration, contrast medium amount and postoperative hospitalization were associated with higher KAP. AAA diameter was the single independent factor related to KAP higher than the median value observed in the study (P=0.013, odds ratio: 3.73, 95% confidence interval: 1.32-10.56).

CONCLUSIONS

This study has identified factors affecting radiation exposure during standard EVAR for infrarenal AAAs. These factors should be taken into account when contemplating AAA repair.

National Diagnostic Reference Levels for Endovascular Aneurysm Repair and Optimisation Strategies

OBJECTIVE

The International Commission on Radiological Protection (ICRP) has highlighted the large number of medical specialties using fluoroscopy outside imaging departments without programmes of radiation protection (RP) for patients and staff. Vascular surgery is one of these specialties and endovascular aneurysm repair (EVAR) is one of the most challenging procedures requiring RP guidance and optimisation actions. The recent European Directive on Basic Safety Standards requires the use and regular update of diagnostic reference levels (DRL) for interventional procedures. The objective of the study was to know the doses of patients undergoing EVAR with mobile Xray systems and with hybrid rooms (fixed Xray systems), to obtain national DRLs and suggest optimisation actions.

METHODS

The Spanish Chapter of Endovascular Surgery launched a national survey that involved hospitals for 10 autonomous communities representing the 77% of the Spanish population (46.7 million inhabitants). Patient dose values from mobile Xray systems were available from nine hospitals (sample of 165 EVAR procedures) and data from hybrid rooms, from seven hospitals, with dosimetric data from 123 procedures. The initial national DRLs have been obtained, as the third quartile of the median values from the different centres involved in the survey.

RESULTS

The proposed national DRLs are 278 Gy cm² for hybrid rooms and 87 Gy cm² for mobile Xray systems, and for cumulative air kerma (cumulative AK) at the patient entrance reference point, 1403 mGy for hybrid rooms, and 292 mGy for mobile systems.

CONCLUSION

An audit of patient doses for EVAR procedures to identify optimised imaging protocol strategies is needed. It is also appropriate to evaluate the diagnostic information required for EVAR procedures. The increase by a factor of 3.2 (for kerma area product) and 4.8 (for cumulative AK) in the DRLs needs to be justified when the procedures are performed in the hybrid rooms rather than with mobile Xray systems.

Editor's Choice - Comprehensive Literature Review of Radiation Levels During Endovascular Aortic Repair in Cathlabs and Operating Theatres

OBJECTIVE

Occupational exposure is a growing concern among the endovascular specialist community. Several types of imaging equipment are available, such as mobile C arms or hybrid rooms, and some have been shown to deliver higher levels of radiation. A literature review was conducted to identify studies reporting dose data during standard (EVAR) and complex abdominal aortic endovascular repair (fenestrated/branched EVAR [F/BEVAR]).

METHODS

A search of the MEDLINE and the Cochrane databases was performed by two independent investigators using the medical subject heading terms "aortic aneurysms", "radiation", and "humans" over a search period of 10 years. Studies with full text available in English and reporting radiation data independently from the imaging equipment type were included. Experimental studies were excluded.

RESULTS

The lowest dose-area product levels during EVAR and F/BEVAR were identified in hybrid rooms, while the highest were with fixed systems. When adherence to the as low as reasonably achievable principles was stipulated by the authors, dose reports tended to be among the lowest. Several studies, especially of F/BEVAR, report concerning levels of radiation for both patients and staff.

CONCLUSION

Modern imaging equipment type, team involvement with radiation management, and the support of recent imaging technologies such as fusion help to reduce the dose delivered during standard and complex EVAR. Investment in modern imaging technology should be considered in every centre providing endovascular management of aortic aneurysms.

Radiation exposure in an endovascular aortic aneurysm repair program after introduction of a hybrid operating theater

BACKGROUND

A hybrid operating theater (HOT) enables optimal image quality, improved ergonomics, and excellent sterility for complex endovascular and hybrid procedures. We hypothesize that the commissioning of a new HOT involves a learning curve. It is unclear how steep the learning curve of these advanced HOTs is. The main purpose of this research was to evaluate radiation exposure parameters in a new HOT for a team of vascular surgeons experienced with infrarenal endovascular aneurysm repair (EVAR) procedures in a conventional operating room with a mobile C-arm. In addition, a comparison of the dose-area product (DAP) achieved in this study and in the literature was made.

METHODS

Before commissioning of the HOT, four vascular surgeons completed a comprehensive HOT training program. From the commissioning of the HOT, clinical and procedural data for all consecutive acute and elective patients treated with EVAR were retrospectively collected for a period of 18 months (January 2016-June 2017). A literature review was conducted of the dose-area product in EVAR procedures performed with a dedicated fixed system or mobile C-arm to analyze how this study performed compared with the literature.

RESULTS

In the 18-month study period, 77 patients were treated with EVAR (59 electively and 18 acutely), from whom the data were obtained. There was no significant change in radiation exposure parameters over time. From the commissioning of the HOT, EVAR procedures were performed with radiation exposure parameters similar to those of studies found in experienced vascular centers using fixed systems.

CONCLUSIONS

Concerning radiation exposure parameters, the commissioning of a new HOT was not accompanied by a learning curve. Radiation exposure parameters achieved in this study were similar to those of studies from experienced and dedicated vascular centers.

Challenges assessing radiation risk in image-guided treatments-implications on optimisation of radiological protection

The present work explores challenges when assessing organ dose and effective dose concerning image-guided treatments. During these treatments considerable x-ray imaging is employed using technically advanced angiographic x-ray equipment. Thus, the radiation dose to organs and the related radiation risk are relatively difficult to assess. This has implications on the optimisation process, in which assessing radiation dose is one important part. In this study, endovascular aortic repair treatments were investigated. Organ dose and effective dose were assessed using Monte Carlo calculations together with a detailed specification of the exposure situation and patient size. The resulting normalised organ dose and effective dose with respect to kerma-area product for patient sizes and radiation qualities representative for the patient group were evaluated. The variability and uncertainty were investigated and their possible impact on optimisation of radiation protection was discussed. Exposure parameters, source to detector distances etc varied between treatments and also varied between image acquisitions during one treatment. Thus the derived normalised organ dose and effective dose exhibited a large range of values depending greatly on used exposure parameters and patient configuration. The derived normalised values for effective dose varied approximately between 0.05 and 0.30 mSv per Gy·cm² when taking patient sizes and exposure parameters into consideration, the values for organ doses exhibited even larger variation. The study shows a possible systematic error for derived organ doses and effective dose up to a factor of 7 if detailed exposure or patient characteristics are not known and/or not taken into consideration. The intra-treatment variability was also substantial and the normalised dose values varied up to a factor of 2 between image acquisitions during one treatment. The study shows that the use of conversion factors that are not adapted to the clinic can cause the radiation dose to be exaggerated or underestimated considerably. A conclusion from the present study is that the systematic error could be large and should be estimated together with random errors. A large uncertainty makes it difficult to detect true differences in radiation dose between methods and technology-a prerequisite for optimising radiation protection for image-guided treatments.