Analysis of intraoperative radiation use in vascular surgery: Catalyst for quality improvement in patient and personnel safety

Introduction

Fluoroscopically guided surgical and endovascular procedures are an integral segment of advances in patient care in the realm of vascular surgery. Over the past decade, the volume of minimally invasive fluoroscopically guided surgical interventions has exponentially increased.^1–6 As the general public’s awareness of the dangers of medical radiation exposure and long-term effects become more prevalent, there is increased state and federal scrutiny to track patient and personnel safety and physician practice patterns.

In general, the risk of radiation-induced stochastic or deterministic injury as a result of medical radiation exposure during these procedures is low. Excessive radiation use in fluoroscopically guided procedures is mainly associated with radiation injury to the skin. However, other potential adverse outcomes of high-dose ionizing radiation include tissue necrosis, cataract formation, infertility, and neoplasia.^7–9 The majority of these high radiation use procedures reported in the literature are from complex cardiac intervention. ¹⁰ Some minimally invasive vascular surgery procedures, such as endovascular abdominal aortic aneurysm repair (EVAR), require subsequent serial computed tomography follow up, which further adds to cumulative level of lifetime radiation exposure. ¹¹

There is paucity in the literature reporting radiation exposures in vascular surgery, especially in the patient-driven era of endovascular therapies. The characterization of radiation exposure to the patient and dose reduction techniques by surgeons in fluoroscopy-guided vascular procedures can help establish quality improvement initiatives. There are a few studies that have documented radiation exposure to patients undergoing fluoroscopy guided minimal invasive interventions.^12–17 Various different subspecialties including urology, orthopedic surgery and interventional radiology have studied the role of radiation usage and dose reduction techniques.^18–23 The goal of this study is to analyze the intraoperative fluoroscopic use in vascular surgery procedures. We will analyze procedure specific radiation exposure rates, body part radiation exposure rates, and high and low dose techniques in fluoroscopically guided vascular surgery operations. These data can serve as baseline information for future quality improvement initiatives for both patient and personnel for radiation safety.

Materials and methods

A retrospective review was undertaken of all intraoperative fluoroscopy-guided vascular surgery procedures performed at Loma Linda University Medical Center extending from January 2010 to January 2017. A total of 318 surgical procedures, utilizing a mobile C-arm from January 2010 to December 2016 were reviewed in this study. Each procedure performed by members of the Division of Vascular surgery is logged into the operative fluoroscopy PACS report. The patient's medical records were then cross-referenced with a log of fluoroscopy time recorded after each procedure and stored in a separate database.

The mobile C-arms used were OEC 9900 Elite (General Electric: GE, USA), OEC 9800 Plus (GE, USA), and OEC 9800 (GE, USA). All image intensifiers were of 12 inches (21 cm) in diameter. The distance between the X-ray tube and patient was about 50 cm, while source-to-image intensifier distance was 100 cm. Fluoroscopy was conducted in a continuous mode, while exposure parameters such as tube voltage, current, and exposure times were controlled by an auto exposure control (AEC). KV range was 40–120 kV_P and mA range was 0.44–20.0 mA. Auto brightness controller was also used. Magnification and collimator functions were explored if necessary, depending on the type of surgery. Roadmap and digital subtraction functions were used for angiography and interventional procedures. The primary data points for each surgical procedure include fluoroscopic time (FT), dose-area-product (DAP), cumulative dose (CD), percentage of magnification of field of view (FOV), percentage of fluoroscopy/roadmap usage, percentage of digital spot/DSA usage, and percentage of film usage. Patient radiation exposure was measured by FT, CD and dose-area product (DAP) value. Patient FT and CD were automatically measured and the value is displayed on monitor. DAP was calculated by multiplying the X-ray beam cross-sectional area field by the absorbed dose in air (air kerma) at a point based on the assumption that the X-ray is equally distributed in terms of absorbed dose, regardless of the location, in a triangle-shaped distribution. Accuracy of the dosimetry was confirmed by comprehensive measurements and consistency checks performed over the course of the study, per hospital protocol.

Each surgical operation was categorized and tabulated based on anatomic surgical field and surgical procedure type. Anatomic surgical fields were categorized into five groups: upper extremity, thoracic, abdomen/pelvic, lower extremity (femoral) and lower extremity (tibial). Procedural types were categorized into 10 categories: angioplasty, atherectomy, bypass, embolization, endarterectomy, filter, fistula, stent, thrombectomy, and other.

Data were analyzed with SPSS v25 (SPSS Inc. Chicago, IL, USA), using descriptive statistics. To evaluate differences in outcome measures among surgery fields and types, the nonparametric Kruskal–Wallis procedure was conducted. All tests of hypotheses were considered to be statistically significant at a p < 0.05.

Results

Three hundred-eighteen vascular surgery cases were included in this study. There were notable trends in all the analyzed radiation usage metrics (FT, CD and DAP) both across the surgical field location and type of surgical procedure. Mean fluoroscopy time was noted to be highest in the abdomen/pelvis (1186.8 s, p < 0.05) compared to all other surgical fields except for the thorax (906.2 s). The lowest mean fluoroscopy time was noted to be in tibial surgical field (318.2 s). When analyzed by surgical type, fluoroscopy time was noted to be highest for atherectomies (2629.6 s, p < 0.05) compared to all other surgical procedures except for embolization (2352.1 s) (Figure 1(a) and (b)).

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Figure 1.

Analysis of fluoroscopy time in vascular surgery procedures. (a) Fluoroscopy time by Anatomic Surgical Field. The abdomen/pelvis procedures demonstrated statistically significantly higher median fluoroscopy time (p<0.05 compared to all other anatomic fields) (b) Fluoroscopy time by Surgical Type. The atherectomy procedure demonstrated the highest fluoroscopy time (2629.6 sec) compared to all other surgical types. Notable other high fluoroscopy time surgical types include angioplasty and embolization.

As expected, when mean CD was analyzed by anatomic field and surgical type, the highest CD was demonstrated in the abdomen/pelvis (352.1 mGy) and embolization procedures (932.5 mGy), respectively (Figure 2(a) and (b)). Conversely, the lowest mean CD was noted to be in femoral surgical field (130.2 mGy) and endartectomy (60.2 mGy).

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Figure 2.

Analysis of cumulative dose in vascular surgery procedures. (a). Cumulative Dose by Anatomic Surgical Field. The highest CD was noted to be in the abdominal/pelvis field. (b). Cumulative Dose by surgical type. As expected, the highest CD are embolization procedures.

Mean dose area product was noted to be the highest in the abdomen/pelvis (18,337 cGy-cm², p < 0.05) compared to all other surgical fields except for the thorax (16,167 cGy-cm²) (Figure 3(a)). Similar to CD, the lowest DAP was seen in the femoral surgical field (8579 cGy-cm²). When DAP was analyzed by surgical type, embolization procedures demonstrated the highest DAP (56,304 cGy-cm²) (Figure 3(b)). Again, endarterectomy (2341 cGy-cm²) demonstrated the lowest DAP.

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Figure 3.

Analysis of dose area product (DAP) in vascular surgery procedures. (a) DAP by Anatomic Surgical Field. DAP for the abdominal/pelvis and thoracic field remain the highest DAP compared to other fields (p<0.05) (b) Dose Area Product by Surgical Type. Embolization demonstrate with the highest DAP (56,305 cGy-cm2). Fistula procedures demonstrated with second highest DAP (18,728 cGy-cm2).

Dose reduction radiation technique usage also demonstrated notable trends. For surgical fields, the percentage of standard fluoroscopy (low dose) versus DSA (high dose) differed based on truncal procedures (abdomen/pelvis and thorax) compared to extremity procedures (upper extremity, femoral and tibial) (Figure 4). Truncal procedures used significantly less DSA compared to extremity procedures. Lower extremity work (femoral and tibial) utilized significantly higher DSA compared to upper extremity. Use of magnification was utilized mostly in the tibial position (Figure 5). Procedures such as surgical bypass were associated with the lowest use of dose reduction techniques. The abdomen/pelvis was associated with the lowest use of dose reduction techniques.

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Figure 4.

Fluoroscopy versus Digital Subtraction Ratios by Surgical Field.

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Figure 5.

Use of Magnification by Anatomic Surgical Field.

Discussion

As endovascular procedures become more prevalent and evolve to more complicated and sophisticated procedures, the safe use and long-term consequences of ionizing radiation exposure must be monitored and studied. Standard ionizing radiation safety principles including ALARA (as low as (is) reasonably achievable) have been well established. ²⁴ Additional radiation safety measures include decreasing fluoroscopy time, use of pulse mode fluoroscopy, decreasing the distance from patient to image intensifier, use of collimation techniques and use of anti-scatter grids. ¹⁶ Lead shielding is currently used to protect physicians and other health care personnel from ionizing radiation exposure although versions of lead drapes can now be installed around the operating table or draped on non-essential parts of the patient to minimize exposure.

In the last decade, there has been increasing study and awareness of the dangers of ionizing radiation use in vascular surgery. Ho et al. ¹⁵ analyzed the use of ionizing radiation in a group of vascular surgeons for a 12-month time frame and found a significant discrepancy was observed for the average hand dose per minute of fluoroscopy among different surgeons. Kendrick et al. ²⁵ did a cohort analysis between fixed and mobile C-arm imaging and concluded that scattered radiation is several-fold higher with fixed units than mobile units across all levels of case complexity. Bannazadeh et al. ⁵ performed a comprehensive review of all endovascular procedures in a fixed C-arm unit during a 30-month period which concluded that increasing complexity of endovascular interventions has resulted in increased radiation exposure to all involved, with the highest doses occurring in aneurysm repairs. ⁵ Given that intraoperative mobile C-arm is still highly used in many vascular surgery practices, our data complement this study and analyze intraoperative mobile C-arm imaging use in 84-month period. The main goal is to establish baseline information for future quality improvement initiatives for patient radiation safety exposure safety.

Standards for reporting and tracking of ionizing radiation use in vascular surgery are currently being developed. There is currently no standard for reporting and recording radiation usage nor is there one for long-term tracking of radiation exposure for patients who require repeat procedures. By convention, most vascular surgeons follow the total fluoroscopy time as a surrogate for amount of radiation that the patient has been exposed to as it is easily understood and is evident on the display during the case. However, fluoroscopy time is not strongly correlated with radiation risk because dose rates for fluoroscopy can be manually or automatically set over a wide range and because a portion of the radiation dose is owing to acquisition of digital images.^26–28

More accurate estimates of absorbed radiation are the dose area product (DAP) and the CD. ²⁶ Dose area product reflects not only the dose within the radiation field but also the area of tissue irradiated, making DAP a much more accurate method compared to fluoroscopy time to monitor the amount of radiation exposure per body area. In reviewing our own data, we note that the surgical procedures with the highest fluoroscopy time were atherectomy procedures (mean 2629.6 s) (Figure 1(b)). However, when the DAP was calculated for all surgical procedures in this study, embolization was noted to have the highest DAP (mean DAP 56,304 cGy-cm²), which was significantly greater compared to all other surgical types (p < 0.05). That the DAP is greater in an embolization in the aorto pelvic procedure compared to an extremity procedure such as an atherectomy is consistent in that the amount and depth of tissue exposed to radiation in the aorto pelvic segment are much greater than that of the extremity.

In this study, we also evaluated the CD among different surgical fields and different surgery types. CD is defined as the total dose from repeated exposure of ionizing radiation to the same portion of the body over a period of time. We demonstrated that in our study population that the highest CD was in the abdomen/pelvis, specifically for embolization procedures (mean 932 mGy). To place into context, this is equivalent to an effective dose of 2400 chest X-rays, 65 head CAT scans, or 1733 commercial flights from London to Tokyo. However, the CD may actually be much higher than reported in our study as we did not account for any additional radiation exposure patients may have experience (e.g. follow-up CTA to assess for efficacy of embolization). We also did not account for any other fluoroscopic procedures such as cardiac catheterizations. Taking all forms of radiation exposure will be a more accurate assessment of a patient’s CD. This may be important since CD may be a surrogate for lifetime radiation exposure, which may have biologic consequence.

It has been suggested that an assessment of several radiation dose metrics for the same procedure is the optimal method to track radiation exposure. ²⁹ For example, if CD is particularly high in a specific instance, an evaluation of fluoroscopy time and the number of images obtained may help to determine whether fluoroscopy time is excessive, an excessive number of images were obtained, or both. Conversely, If DAP is high but CD is within the acceptable range, this finding may indicate insufficient collimation.

Despite the use of current ionizing radiation safety techniques, it has been reported that radiation exposure to both physician and patients is not negligible. Lipsitz et al. ¹⁶ reported that the annual effective dose to vascular surgeons is 1.52 mSV but is 7.77 mSV around the eyes and 18.69 mSV in the hands. ¹⁶ This is important because it has been suggested that fatal cancer risk has a linear relation with an effective dose at >100 mSv, which is estimated at 5% per 1000 mSv exposed. ³⁰ Other predictive models such as the suggested by the International Commission on Radiological Protection (ICRP) and the National Council on Radiation Protection and Measurement (NCRP) suggest that lifetime dose of 200 mSv would increase the risk of fatal cancer to 21%.

The lifetime exposure to ionizing radiation is becoming more relevant as younger and younger patients are being exposed to endovascular therapies. Combining those therapies with their subsequent surveillance studies such as CTA may lead to lifetime effective dose that nears that predicted for fatal cancers. Furthermore, as endovascular therapies become more sophisticated to develop longer and more complex procedures such as fenestrated endovascular aortic repair (FEVAR) or endovascular branched endografts, the lifetime effective dose for vascular surgeons may be much higher than previously reported. A recent study by El-Sayed et al. ³¹ demonstrated the presence of acute DNA damage in the lower extremities of the interventionalist performing the EVAR, a region of the body classically not protected by lead shielding. The damaged cellular DNA markers returned to baseline after 24 h and the long-term sequelae of intermittent DNA damage were not available in this particular study. ³¹ However, this study hallmarks the danger of ionizing radiation exposure not only to the practitioners but to our patients, who are frequently not shielded with lead during endovascular procedures.

We acknowledge that there are limitations of this study. First, data were collected in a single tertiary academic institution, representing cases from a specific type of vascular surgery practice. Second, we did not record skin dose monitoring in our patients. Skin dose monitoring would be a stronger data set to calculate the radiation exposure. However, in real-world settings, this is not done by any service that utilizes ionizing radiation including diagnostic radiology, interventional radiology, cardiology, urology or orthopedics. Our goal is to establish baseline radiation metrics that can be universally tracked and reported. Third, surgeon radiation use techniques implemented in these operative settings may change over time (with increasing education and awareness of radiation use), which introduces bias that might limit the generalizability of our results.

Conclusions

Exposure to ionizing radiation by patients and vascular surgeons is increasing as endovascular procedures evolve and become more sophisticated. There were notable trends in the analyzed radiation usage variables both across the surgical field location and type of surgical procedure. Specifically, cases that involve the abdomen/pelvis, embolization and atherectomy have the highest radiation use. These types of cases can be targeted for future increased dose reduction techniques or staged procedures. Understanding and tracking the proper exposure metrics, such as DAP per case rather than FT, are essential in preventing unnecessary exposure and biologic sequelae of ionizing radiation. Standardized tracking metrics and reporting should be a quality measure initiative for all institutions performing endovascular procedures. Our goal is to bring awareness to these topics and to emphasize the needs for critical evaluation of radiation use in all types of vascular surgery.