Keywords
Endoscopic retrograde cholangiopancreatography - fluoroscopy - ionizing radiation - radiation
Introduction
Fluoroscopy guidance is widely employed in the field of gastroenterology, particularly by specially trained gastroenterologists for endoscopic retrograde cholangiopancreatography (ERCP), a procedure with diagnostic and therapeutic benefits in pancreatobiliary disease. A C-arm is an intraoperative source of fluoroscopic X-ray, named for its C-shaped body. When performing an ERCP, a C-Arm is placed adjacent to a patient's bed so that the X-ray source is below the patient and an X-ray detector is above the patient. Unfortunately, this comes with the risk of ionizing radiation to all those involved in the case, including endoscopists, anesthesiologists, anesthetists, nurses, and techs working in close proximity to the scattered radiation from the patient. Ionization can cause DNA damage and cell death, leading to cancer and genetic defects. The longer the radiation exposure and the higher the radiation levels, the more likely one is to experience these consequences. Thus, the Nuclear Regulatory Commission (NRC) set an occupational dose limit of 50 millisievert (mSv) effective doses per year.[1] On average, an endoscopist receives an effective dose of 0.07 mSv per ERCP, which uses approximately 8 minutes of fluoroscopy time.[2]
[3] While this effective dose is small in relation to the annual dose limit, some of the most serious adverse effects of radiation, including those mentioned above, can occur with any level of exposure.[2] Studies have demonstrated the benefit of protective equipment but this is subject to improper use and inconsistency by the user. The most effective way to mitigate exposure would obviously be to reduce emissions. Our study investigates the effect that updating our C-Arm will have on radiation exposure by comparing the ionizing radiation effects of the OEC 9900 Elite to the newer OEC Elite.
Methods
We replicated the layout of a typical ERCP in our endoscopy suite with a C-Arm adjacent to a fluoroscopy bed containing a stack of acrylic plates to simulate our patient and create radiation scatter ([Fig. 1]). Using a Fluke 451 Ion Chamber Survey Meter, we measured energy output in Kilovoltage peak (kVp) and Milliamperage (ma) and levels of radiation in the air as milliroentgen per hour (mR/h). Measurements were obtained at the bedside, 33 inches from the center of the bed to simulate the position of the endoscopist and at the head of the table, 46 inches from the center of the bed to simulate the position of the anesthetist. The same arrangement and measurements were completed with the OEC 9900 Elite and the OEC Elite. For each C-Arm and position, we calculated mSv/h with continuous and pulsed fluoroscopy. Millisievert per hour can easily be calculated from milliroentgen per hour (mR/h) as 1.0 mR is equal to 0.0087 mSv.
Fig. 1 Room Arrangement, with and without C-Arm. This figure illustrates the spatial arrangement used in our study to replicate a typical ERCP with the locations of radiation measurement marked by letters A and B. On the left, the layout is shown without the C-Arm in place. On the right, the setup is complete with the C-Arm in location for obtaining data. ERCP, endoscopic retrograde cholangiopancreatography.
Results
At each position, the OEC Elite emitted less energy and ionizing radiation or potential for radiation-induced harm than the OEC 9900 Elite. Continuous imaging with OEC 9900 Elite emitted 0.12 mSv/h at the head of the bed and 0.49 mSv/h at the bedside, while the OEC Elite emitted only 0.04 mSv/h and 0.14 mSv/h, respectively ([Table 1]). With pulsed imaging, the differences between the OEC 9900 Elite and OEC Elite were smaller; however, the OEC Elite still emitted less radiation at both locations.
Table 1
Energy output and stochastic risk of each C-arm
|
OEC 9900 Elite
|
OEC Elite
|
|
Head of bed (46”)
|
Bedside (33”)
|
Head of bed (46”)
|
Bedside (33”)
|
|
Continuous
|
Pulse
|
Continuous
|
Pulse
|
Continuous
|
Pulse
|
Continuous
|
Pulse
|
|
mR/h
|
14.0
|
3.4
|
56.0
|
11.4
|
4.2
|
2.90
|
15.5
|
10.2
|
|
mSv/h
|
0.123
|
0.030
|
0.491
|
0.100
|
0.037
|
0.025
|
0.136
|
0.089
|
|
kVp
|
71.0
|
74.0
|
71.0
|
75.0
|
62.0
|
61.0
|
62.0
|
61.0
|
|
mA
|
2.3
|
2.5
|
2.3
|
2.5
|
1.8
|
4.7
|
1.7
|
4.7
|
Abbreviations: kVp, Kilovoltage peak; mA, milliamperage; mR/h, milliroentgen per hour; mSv/h, milliSievert per hour.
Note: This table depicts the energy output in kVp and mA as well as the measurement of radiation in a volume of air (mR/h) with the associated stochastic biological risk (mSv/h) for each device, image mode, and location.
Discussion
With an average of 8 minutes of fluoroscopy time per ERCP and ∼850 ERCP cases done annually in our endoscopy center, these differences become more significant. Continuous fluoroscopy imaging with OEC 9900 Elite produces 13.92 mSv/year at the head of the bed and 55.60 mSv/year at the bedside ([Table 2]). However, the OEC Elite produces 4.18 mSv/year and 15.41 mSv/year at respective locations. Our measurements in this study are not “effective doses” as they are not the weighted sums of radiation doses on relevant organs and tissues, thus they cannot be readily compared with the annual effective dose limit set by the NRC. Instead, they serve to demonstrate the difference in ionizing radiation at one point in space, which is a surrogate to show that annual ionizing radiation dose and stochastic biological risk (radiation-induced cancer risk) are strongly influenced by C-Arm choice.
Table 2
Risk of ionizing radiation associated with endoscopic retrograde cholangiopancreatography
|
OEC 9900 Elite
|
OEC Elite
|
|
Head of bed (46”)
|
Bedside (33”)
|
Head of bed (46”)
|
Bedside (33”)
|
|
Continuous
|
Pulse
|
Continuous
|
Pulse
|
Continuous
|
Pulse
|
Continuous
|
Pulse
|
|
mSv/h
|
0.123
|
0.030
|
0.491
|
0.100
|
0.037
|
0.025
|
0.136
|
0.089
|
|
mSv/case
|
0.016
|
0.004
|
0.065
|
0.013
|
0.005
|
0.003
|
0.018
|
0.012
|
|
mSv/year
|
13.915
|
3.379
|
55.660
|
11.331
|
4.175
|
2.882
|
15.406
|
10.138
|
Abbreviation: ERCP, endoscopic retrograde cholangiopancreatography.
Note: This table depicts stochastic biological risk of ionizing radiation in rates of millisievert. These values are shown in rates per hour, case, and year. In this study, a case represents 8 minutes of fluoroscopy time, which is the average amount needed for one ERCP. A year consists of 850 ERCP cases, which is the approximate ERCP case load in our Endoscopy Center.
Conclusion
This study supports the well-established principle that the greater the distance at which a staff member stands from the location from where X-rays enter the patient, the lower their radiation exposure will be. Similarly, using pulsed imaging mode lowers scatter radiation exposure. Unique to this study is the demonstration that the OEC Elite operated at a lower energy output (kVp and mA) than the OEC 9900 Elite, which resulted in lower scatter radiation exposure. While the radiation dose per ERCP case with either C-Arm in our study seems relatively low, particularly when compared with the annual effective dose limit, endoscopists should be adopting the practice of “as low as reasonably achievable.” This is a widely accepted principle in the field of radiation safety, encouraged by national and international radiation safety agencies.[4] In all avenues, it is a good practice to use the least amount of radiation to get the results, data, and images deemed necessary to complete an intervention. In this case, we have strong evidence to suggest that you can reduce exposure to radiation by upgrading from an OEC 9900 Elite to an OEC Elite.
