JBJS | Radiation Exposure With Use Of the Inverted-C-Arm Technique in Upper-Extremity Surgery

The Journal of Bone & Joint Surgery, Volume 83, Issue 5

Articles | May 01, 2001

Radiation Exposure With Use Of the Inverted-C-Arm Technique in Upper-Extremity Surgery

Michael R. Tremains, MD; Gregory M. Georgiadis, MD; Michael J. Dennis, PhD

Investigation performed at the Departments of Orthopaedic Surgery and Radiology, Medical College of Ohio, Toledo, Ohio
Michael R. Tremains, MD Gregory M. Georgiadis, MD Michael J. Dennis, PhD Departments of Orthopaedic Surgery (M.R.T. and G.M.G.) and Radiology (M.J.D.), Medical College of Ohio, 3065 Arlington Avenue, Toledo, OH 43614. E-mail address for M.R. Tremains: mtremains@netscape.net. E-mail address for G.M. Georgiadis: ggeorgiadis@mco.edu
No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. No funds were received in support of this study.
A commentary is available with the electronic versions of this article, on our web site (www.jbjs.org) and on our CD-ROM (call 781-449-9780, ext. 140, to order).

The Journal of Bone & Joint Surgery. 2001; 83:674-678

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Abstract

Background: Intraoperative fluoroscopy is commonly used in surgical procedures on upper extremities. We compared radiation exposure from two possible positions of the mobile digital fluoroscopy unit (c-arm): (1) the standard technique, with the x-ray tube down (near the floor) and the image intensifier at the top of the c-arm, and (2) the inverted position, in which the image intensifier is used as a table and the x-ray tube is up.

Methods: A commercially available c-arm was used to irradiate a phantom hand in one of three configurations. In the first, the phantom hand was placed on an armboard equidistant from the x-ray tube and the image intensifier with the beam directed upward. In the second, the c-arm was inverted with the beam directed downward and the image intensifier used as a table. The third configuration was identical to the second except that a magnified image was used. Radiation exposure was measured at four locations corresponding to the approximate position of the surgeon’s head, chest, and groin and the patient’s hand.

Results: The amount of radiation exposure to both the surgeon and the patient was significantly less when the c-arm was used in the inverted position (p < 0.0001). The dose rate to the patient’s hand was reduced by 59%. The radiation exposure to the surgeon’s head, body, and groin with the inverted-c-arm technique was 67%, 45%, and 15% of the measured doses with the x-ray-tube-down configuration. When we used the magnification mode of the image intensifier, with its correspondingly smaller field size, the doses were further reduced to 46%, 32%, and 11% of the standard-configuration values.

Conclusions: Use of the inverted-c-arm technique with the image intensifier as an operating table can significantly reduce radiation exposure to the surgeon and the patient during surgical procedures on upper extremities.

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Introduction

Introduction | Materials and Methods | Results | Discussion | References

The mobile digital fluoroscopy unit, the so-called c-arm, is commonly used as an intraoperative aid in modern orthopaedic surgery. Over the past two decades a number of investigators have examined the use of fluoroscopy in orthopaedics; the radiation risks to surgical personnel and measures that can be taken to prevent excessive exposure have been explored^1-8.

The c-arm is typically deployed with the x-ray tube near the floor and the radiation beam directed upward toward an image receptor system or image intensifier. The use of an inverted position (x-ray tube up), in which the image intensifier acts as an operating table, has been described for surgical procedures on upper extremities². This configuration can potentially decrease fluoroscopy time by decreasing the number of missed images due to extremity positioning. However, some authors have advised against this practice, citing increased radiation exposure and possible equipment damage^9-12.

We wished to know whether the senior author’s (G.M.G.) routine use of the image intensifier as a table in upper-extremity surgical procedures resulted in increased radiation exposure to the patient and surgeon. The purpose of this study was to compare the radiation levels associated with the standard and the inverted-c-arm positions, with use of setups that simulated clinical conditions.

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Fig. 1:: The experimental setup in configuration A. The c-arm was positioned with the x-ray tube (A) near the floor. The x-ray beam (arrows) was directed upward through an armboard (D) to the phantom hand (C) and the image intensifier (B).

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Fig. 2:: The experimental setup in configurations B and C. The x-ray tube (A) is at the apex of the c-arm, and the radiation beam (arrows) is directed downward to the phantom hand (C) that is resting on the image intensifier (B).

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TABLE I: Radiation Exposure for Configurations A, B, and C*

*Mean and standard deviation of three measurements.

	Configuration A	Configuration B	Configuration C
Simulated patient entrance dose (mGy/min)	7.27 ± 0.16	2.98 ± 0.24	2.89 ± 0.21
Simulated surgeon dose (mGy/hr)
Head	0.369 ± 0.015	0.248 ± 0.014	0.170 ± 0.022
Chest	0.466 ± 0.004	0.211 ± 0.010	0.148 ± 0.016
Groin	0.367 ± 0.010	0.055 ± 0.007	?0.039 ± 0.0015

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TABLE I: Radiation Exposure for Configurations A, B, and C*

*Mean and standard deviation of three measurements.

	Configuration A	Configuration B	Configuration C
Simulated patient entrance dose (mGy/min)	7.27 ± 0.16	2.98 ± 0.24	2.89 ± 0.21
Simulated surgeon dose (mGy/hr)
Head	0.369 ± 0.015	0.248 ± 0.014	0.170 ± 0.022
Chest	0.466 ± 0.004	0.211 ± 0.010	0.148 ± 0.016
Groin	0.367 ± 0.010	0.055 ± 0.007	?0.039 ± 0.0015

Materials and Methods

Introduction | Materials and Methods | Results | Discussion | References

Study Design

A commercially available mobile fluoroscopy unit (OEC series 9400; OEC Medical Systems, Salt Lake City, Utah) was used in this study. This system has a trimode image intensifier with a field of view selectable at 23 cm (normal image), 15 cm (first magnified image), or 11 cm (second or most magnified image). The unit has an x-ray focal-spot-to-image-intensifier distance fixed at 90 cm and a 2-cm faceplate on the image intensifier for a backside laser pointer. A typical radiographic setting for upper-extremity imaging is 55 kVp and 1.5 mA. All measurements were made at these settings.

Radiation scatter from a patient was simulated with use of an acrylic-and-bone phantom hand model with the x-ray beam centered on the base of the second metacarpal. This phantom is often used for radiographer training because it is a good representation of the size, shape, attenuation, and scatter properties of a patient’s hand and wrist. Acrylic has approximately the same effective atomic number and density as human soft tissue and is routinely used as a patient attenuator and scatter source in radiographic system measurement¹³.

Two devices were used to record radiation. First, the Keithley Model-35000 radiation dosimeter (Inovision Radiation Measurements, Cleveland, Ohio) was used to record radiation directly in the path of the beam. A second device, the Keithley Model-36150 ionization type survey meter (Inovision Radiation Measurements) was used to record radiation scatter at various distances from the phantom hand. Both of the Keithley units measure radiation as a rate (milliroentgens per minute or milliroentgens per hour). Therefore the results do not include any potential differences due to total exposure time. The results were then converted to SI units (milligrays).

Three c-arm configurations were studied, with three separate readings recorded for each. For configuration A, a phantom hand was placed on an armboard equidistant from the x-ray tube and the image intensifier (Fig. 1). The vertical x-ray beam was directed toward the ceiling with the use of a 23-cm field of view to simulate the clinical situation in which a hand is placed on a radiolucent armboard and the c-arm is used in a standard fashion. Configuration B consisted of an inverted-c-arm setup with a 23-cm field-of-view setting (Fig. 2) to simulate the clinical situation in which the c-arm is used as a table. Configuration-B images appeared smaller than those of A because the phantom hand was closer to the image intensifier. The B configuration and a 15-cm field of view were used for the C configuration, resulting in images of nearly the same size and resolution as those from configuration A.

The Keithley Model-35000 radiation dosimeter was used to measure the amount of radiation entering the phantom hand in each of the three configurations. This device replaced the phantom hand on the armboard or on the image intensifier. Configuration-A readings were taken at a distance of 45 cm above the x-ray tube through a 5-cm plastic-and-foam armboard. The measurements for B and C were taken at a distance of 90 cm below the x-ray tube, directly on the image intensifier.

The Keithley Model-36150 unit was used to measure the scatter radiation given off from the phantom hand at three additional locations. The first was at a distance 50 cm directly parallel to the phantom hand. The next two measurements were made 30 cm directly above and below this first location. These locations were arbitrarily chosen after a series of measurements were made of one of us (M.R.T.) positioned in the operating room as he would be sitting adjacent to the c-arm unit during a surgical procedure. The locations represented the approximate areas of the surgeon’s chest, head and neck, and groin. At each of these locations, three separate readings were taken for configurations A, B, and C.

Statistical Analysis

The data were analyzed statistically with use of the Student t test and multiple analysis of variance, as indicated. Analysis of variance was used to determine whether there was a significant difference among the readings for configurations A, B, and C for each location at which radiation levels were measured. The Student t test was employed to determine whether there was a significant difference between the simulated head and groin measurements within each group. The means and standard deviations for all measured parameters were analyzed.

Results

Introduction | Materials and Methods | Results | Discussion | References

Table I shows the means and standard deviations of three sets of radiation exposure measurements at the target sites for configurations A, B, and C. The radiation readings recorded for both of the inverted c-arm configurations (B and C) were significantly decreased when compared with those of configuration A at all locations (p < 0.0001). For example, compared with the measurements in configuration A, the radiation doses to the expected positions of the surgeon’s head, chest, and groin areas were 67%, 45%, and 15% of the measured doses in configuration B and 46%, 32%, and 11%, respectively, in configuration C. The dose rate to the simulated patient’s hand was 60% less.

There was a small decrease in the radiation recorded for configuration C as compared with that of B at all locations. This decrease was found to be significant at the simulated positions of the surgeon’s head and chest (p < 0.0001). However, with the numbers available, no significant decrease could be detected at the level of the groin. There was also significantly less radiation exposure at the groin level than at the head level when the inverted configurations were used (p < 0.0001 for B and p < 0.0009 for C). This difference was not present when configuration A was used.

Discussion

Introduction | Materials and Methods | Results | Discussion | References

When fluoroscopy is employed in upper-extremity surgical procedures, a radiolucent table is often used as a surgical platform. The c-arm unit is then brought into the operative field in an upright position with the x-ray tube below the table. This approach has the potential disadvantage of increased surgical time due to the need to reposition the c-arm. An alternative setup is to invert the c-arm and use the large image-intensifier portion as a surgical table, as described by Hanel and Robson². Once the unit is draped under sterile conditions and initial images are made, repositioning of the x-ray unit is unnecessary. The surgeon can reposition the involved extremity on the image intensifier as desired for additional views.

Despite the potential advantages of this inverted-c-arm technique, authors of previous studies have advised against its use. Waseem and Kenny thought that there was a major risk of accidentally drilling through the image intensifier, with potentially disastrous results¹². Other surgeons have echoed these concerns^9,10. However, the senior author (G.M.G.) routinely uses the inverted-c-arm technique for any surgical procedure on the hand, wrist, forearm, or elbow, in both adults and children, that requires intraoperative fluoroscopy; he has never encountered a problem, but the risks of inadvertent damage to the fluoroscopy unit should not be minimized. Use of a radiolucent pad on top of the image intensifier can decrease the possibility of damage during surgery. One author recommended a simple commercially available polyethylene chopping board⁹.

Rules governing the use of the c-arm in the United Kingdom suggest that the radiation source should be placed below the patient and the image intensifier should be placed above the patient¹⁴. However, results of a recent study by Van Staden et al. are in agreement with our data, confirming a decrease in radiation exposure with the c-arm set up in the inverted position, with the radiation source up¹¹. In that study the image intensifier was not used as a table but instead was placed immediately underneath a radiolucent hand-table.

Authors of previous studies of radiation exposure during fluoroscopy have recommended that operating-room personnel remain a minimum of 46 to 70 cm from the x-ray beam^1,4. People working more than 90 cm from the beam have been considered to be at low risk for radiation exposure⁴. The surgeon may often be within this radius and can be subjected to a large amount of scatter (radiation bouncing off the patient). Giachino and Cheng found scatter to be a major factor in the exposure of surgeons to radiation¹. In contrast, the major source of radiation to the patient’s extremity is the beam itself¹⁵.

In most fluoroscopic units, collimation (narrowing of the x-ray beam) occurs automatically with magnification. This has been shown to decrease scatter radiation⁷, although we are not aware of any quantitative studies demonstrating the amount of reduction achieved. Leakage from the x-ray-tube housing is a minor source of radiation to personnel. The major source is scatter from objects in the path of the beam¹⁵. These objects are primarily the patient and the table and secondarily the image intensifier. The most important factor affecting exposure of objects in the path of the beam to radiation is their distance from the x-ray tube and the x-ray technique used. For structures outside of the beam, the most important factors are distance from the scatter source, the x-ray technique, and the x-ray field size.

The results of our study show that the inverted-c-arm technique may significantly reduce the radiation dose to both the surgeon and the patient. The distance between the x-ray tube and the phantom hand was approximately doubled in configurations B and C. This distance led to a reduction in exposure that follows the inverse square law, which describes the reduction in radiation intensity with increasing distance from the x-ray source^3,15. The x-ray-tube-down configuration may increase scatter because of the presence of the acrylic-and-foam arm support, which was not present in configurations B and C. When magnification was added to the inverted setup, another significant decrease in exposure occurred at the simulated locations of the surgeon’s head and body. This further reduction in dose was due to collimation and a subsequent decrease in scatter even though there was little effect on the readings directly in the path of the x-ray beam⁷. The doses delivered to the chest were higher than those delivered to the head or groin because of the proximity of the chest to the scattering source at all configurations. This scattered radiation, although now redirected, continues to follow the inverse square law. Since the simulated head and groin areas are equal distances from the scattering source, equivalent dose measurements might be expected. However, very low radiation values were measured at the simulated groin level with the inverted technique. This may have been due to both the increased x-ray tube-to-target distance and a shielding effect from the large metallic image intensifier. The housing of the image intensifier is physically between the scattering source and the expected location of the lower body of the surgeon; thus it acts as a radiation barrier.

These results do not apply to fluoroscopy during surgical procedures on the lower extremities^4,5. The use of the image intensifier as a table is not practical for operating on the pelvis. Therefore, the advantage achieved by increasing the distance of the x-ray tube from the patient and surgeon is lost. In addition, the patient’s anatomy acts as a major radiation attenuator or shield when thick body parts are imaged, resulting in less scattered radiation on the image-intensifier side of the patient.

Our study had several limitations. These include its nonclinical nature and the use of synthetic targets. As a result, we were unable to document theoretical decreases in surgical time, which may further reduce radiation exposure when the inverted c-arm is used. Our results were not compared with radiation exposures found in previous studies. We decided that this would be of limited value because of the large variation in quantitative readings⁶. Another limitation of our study was that, because we used a single type of fluoroscopy unit, we did not take into account the different automatic columnization settings or different sizes of the image intensifier seen with other units. Operating-room draping techniques vary greatly, but we did not consider this a potentially important variable. Finally, we did not evaluate the risk of damage to the c-arm in the inverted position¹², although a radiolucent protective pad should reduce the chances of this occurring.

In summary, we compared the use of two different setups for the mobile fluoroscopic unit. Our results contradict those of previous investigations that have suggested that the inverted-c-arm position increases the surgeon’s exposure to radiation^4,5. Although the inverted position may potentially increase exposure when used for operations on the lower extremities, the use of the image intensifier as a table in upper-extremity surgery reduces the patient’s radiation exposure. This configuration and the use of customary techniques such as magnification and collimation can potentially dramatically decrease the radiation risk to both the patient and the surgeon. The image intensifier, when used as a table, can additionally provide further shielding to the surgeon’s groin area. We believe that the results of our study support the use of the inverted-c-arm technique when intraoperative fluoroscopic images are needed in upper-extremity surgical procedures.

Note: The authors thank Roy Schneider for the medical illustrations and Sadik A. Khuder, PhD, for the statistical analysis.

References

Introduction | Materials and Methods | Results | Discussion | References

Giachino AA, and Cheng M: Irradiation of the surgeon during pinning of femoral fractures. J Bone Joint Surg Br,1980.62: 227-9, 62227 1980 [PubMed]

Hanel DP, and Robson DB: The image intensifier as an operating table. J Hand Surg [Am],1987.12: 322-3, 12322 1987 [PubMed]

Levin PE; Schoen RW Jr; and Browner BD: Radiation exposure to the surgeon during closed interlocking intramedullary nailing. J Bone Joint Surg Am,1987.69: 761-6, 69761 1987 [PubMed]

Mehlman CT, and DiPasquale TG: Radiation exposure to the orthopaedic surgical team during fluoroscopy: "how far away is far enough?". J Orthop Trauma,1997.11: 392-8, 11392 1997 [PubMed][CrossRef]

Miller ME; Davis ML; MacClean CR; Davis JG; Smith BL; and Humphries JR: Radiation exposure and associated risks to operating-room personnel during use of fluoroscopic guidance for selected orthopaedic surgical procedures. . J Bone Joint Surg Am,1983.65: 1-4, 651 1983 [PubMed]

Riley SA: Radiation exposure from fluoroscopy during orthopaedic surgical procedures. Clin Orthop,1989.248: 257-60, 248257 1989 [PubMed]

Riley RC; Birks JW; Palacios E; and Templeton AW: Exposure of radiologists during special procedures. Radiology,1972.104: 679-83, 104679 1972 [PubMed]

Sanders R; Koval KJ; DiPasquale T; Schmelling G; Stenzler S; and Ross E: Exposure of the orthopaedic surgeon to radiation. J Bone Joint Surg Am,1993.75: 326-30, 75326 1993 [PubMed]

Matthews MG: The image intensifier as an operating table: a dangerous practice [letter]. J Bone Joint Surg Br,2000.82: 774, 82774 2000 [PubMed][CrossRef]

Sharpe IT, and Van Staden G: The image intensifier as an operating table: a dangerous practice [letter]. J Bone Joint Surg Br,2000.82: 774-5, 82774 2000 [PubMed][CrossRef]

Van Staden G; Farrant K; Richards R; and Bunker T: Image intensifier position for hand and wrist fractures. Injury,2000.31: 351-2, 31351 2000 [PubMed][CrossRef]

Waseem M, and Kenny NW: The image intensifier as an operating table: a dangerous practice. J Bone Joint Surg Br,2000.82: 95-6, 8295 2000 [PubMed][CrossRef]

American Association of Physicists in Medicine. Report 31: Standardized methods for measuring diagnostic x-ray exposures. New York: American Institute of Physics; 1990. p 10

Royal Devon and Exeter Healthcare NHS Trust. Local rules for use of ionising radiation. Appendix 3: Special local rules for mobile and portable x-ray units. Exeter, UK: Royal Devon and Exeter Hospital (Wonford); 1995

Bushberg JT, Seibert JA, Leidholdt EM Jr, Boone JM. The essential physics of medical imaging. Philadelphia: Williams and Wilkins; 1994. p 583-632

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TABLE I: Radiation Exposure for Configurations A, B, and C*

*Mean and standard deviation of three measurements.

	Configuration A	Configuration B	Configuration C
Simulated patient entrance dose (mGy/min)	7.27 ± 0.16	2.98 ± 0.24	2.89 ± 0.21
Simulated surgeon dose (mGy/hr)
Head	0.369 ± 0.015	0.248 ± 0.014	0.170 ± 0.022
Chest	0.466 ± 0.004	0.211 ± 0.010	0.148 ± 0.016
Groin	0.367 ± 0.010	0.055 ± 0.007	?0.039 ± 0.0015

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TABLE I: Radiation Exposure for Configurations A, B, and C*

*Mean and standard deviation of three measurements.

	Configuration A	Configuration B	Configuration C
Simulated patient entrance dose (mGy/min)	7.27 ± 0.16	2.98 ± 0.24	2.89 ± 0.21
Simulated surgeon dose (mGy/hr)
Head	0.369 ± 0.015	0.248 ± 0.014	0.170 ± 0.022
Chest	0.466 ± 0.004	0.211 ± 0.010	0.148 ± 0.016
Groin	0.367 ± 0.010	0.055 ± 0.007	?0.039 ± 0.0015