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echniques to Minimizentraoperative Radiation Exposure. Bryan Butler, MD, and Kornelis A. Poelstra, MD, PhD

The use of fluoroscopic visualization during spinal procedures may subject both the patientand the surgical team to considerable amounts of X-rays. A number of factors are known toinfluence the radiation doses administered to these individuals, many of which are relatedto the specific settings of the C-arm such as beam energy, collimation, and tube current,whereas others involve external variables including proper positioning of the image inten-sifier, protective shielding, and the implementation of appropriate monitoring protocols. Byincorporating these safety measures, it may be possible to achieve significant reductionsin the exposures of the patient and surgeon alike.Semin Spine Surg 20:181-185 © 2008 Elsevier Inc. All rights reserved.

KEYWORDS radiation, exposure, minimize, spine, intraoperative, fluoroscopy

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espite the many advantages associated with intraopera-tive fluoroscopic visualization, it is clear that the use of

his imaging approach has the potential to expose the patientnd the operating room staff to substantial amounts of radi-tion, predisposing them to the development of numerousadiation-induced complications that were elucidated in therevious article. However, with a thorough understanding ofhe physics underlying the transmission of X-rays, adoptionf proper C-arm imaging techniques, and adherence to ap-ropriate safety regulations, it may be possible to effectivelyecrease the magnitude of the doses that are administered tohese individuals. The purpose of this review is to discuss thearious strategies that have been established to minimize theuantities of ionizing radiation that are emitted during fluo-oscopically assisted procedures and reduce the risks to theatient and surgeon alike.

actors That Mayinimize Patient Exposure

eam Energy and Tube Currenteam energy (peak kilovoltage) and tube current (milliam-eres) play an important role in determining the dose that isbsorbed by the patient. By employing higher peak kilovolt-

epartment of Orthopaedics, University of Maryland–Shock Trauma,Baltimore, MD.

ddress reprint requests to Kornelis A. Poelstra, MD, PhD, Department ofOrthopaedics, University of Maryland–Shock Trauma, 22 S. Greene

pStreet, Suite 11B, Baltimore, MD 21201. E-mail: kpoelstra@gmail.com

040-7383/08/$-see front matter © 2008 Elsevier Inc. All rights reserved.oi:10.1053/j.semss.2008.06.004

ges, a C-arm is able to generate an X-ray beam of highernergy that is able to penetrate the tissues more easily with amaller tube current, resulting in less exposure to the pa-ient.1 In contrast, attenuating the beam energy by decreasinghe peak kilovoltage requires that the tube current be in-reased to produce images of acceptable quality. Unfortu-ately, any loss of beam strength is normally accompanied by corresponding decline in image contrast.

ollimationestricting the X-ray field to the area of interest serves to

mpede the dissemination of scattered radiation, which limitshe exposure of any adjacent structures.1 Adjusting the colli-ation of the beam may also improve the resolution of the

cquired images.

ource-to-Skin Distanceccording to the inverse square law, increasing the intervaletween the X-ray tube and the skin significantly lowers theoses that are absorbed by patients, so maximizing this dis-ance represents one of the most reliable methods for miti-ating their exposure.1 Since the beam source is further awayrom the operative site, this strategy also provides the addedenefit of expanding the field of view.

kin-to-Image Intensifier Distanceimilar reductions in the amount of radiation absorbed byhe patient may also be achieved by placing the image inten-ifier as close to the relevant anatomy as space allows.1 This

ractice narrows the void that the emitted X-rays must tra-

181

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182 R.B. Butler and K.A. Poelstra

erse before they are collected by the receiver, which mini-izes both the dose rate as well as the cumulative dose of

hese individuals. Unfortunately, decreasing this distanceay actually obscure visualization to a certain extent becauselarger fraction of scattered radiation that would otherwiseave diverged away from the photoreceptor may be capturednd incorporated into the images.

mage Magnificationnlarging the size of the image clearly adds to the exposure of

he patient. Manipulation of the fluoroscopic projections maye accomplished either geometrically or electronically; geo-etric magnification is achieved by moving the receiver away

rom the sterile field, which necessarily brings the X-ray tubeloser to the patient, while electronic magnification entailsocusing the source beam so that it completely covers theutput layer of the image intensifier. Each of these ap-roaches will subject a patient to more radiation, althougheometric magnification increases the dose to a greater ex-ent.1

ridshese attachments are designed to improve image contrast byrecluding attenuated X-rays from being detected by the re-eptor. Because grids may more than double the patient’sose, these appliances should not be utilized in situationshere there is little scattered radiation (eg, smaller individu-

ls, longer patient-to-image intensifier distances).

eam-on Timeiven that the patient exposure is directly proportional to theumber of seconds that the fluoroscope is energized, consid-rable dose reductions may be obtained by simply minimiz-ng the time that the beam is active. For example, a surgeryhat requires 30 minutes of fluoroscopic imaging may deliverdose as high as 15 Gy (1500 rad), which may be sufficient

o engender severe radiation-induced skin complications.2

or this reason, it may be preferable to replace continuous-arm visualization with short, intermittent bursts.1

atient Sizeith heavier patients, a greater percentage of the X-ray beam

s either absorbed by the surrounding tissues or reflected offhe surface of the skin. Consequently, these cases are associ-ted with higher exposures because the peak kilovoltage andube current must be amplified to maintain acceptable levelsf brightness, contrast, and detail. In addition, obese individ-als are also more likely to develop superficial burns as aesult of the elevated entrance doses that exist secondary tohe more extensive scattered radiation that is typically ob-erved in conjunction with this condition.1 Although the sizef a patient undoubtedly influences the amount of radiationhat is ultimately received, it may be exceedingly difficult to

lter this variable in a meaningful way before the operation. F

actors that Mayinimize Surgeon Exposure

ompared with patients who may undergo significant irradi-tion as part of a fluoroscopically assisted intervention, sur-eons are generally subjected to fewer X-rays because theyre not in the direct path of the incident beam. Before dis-ussing the specific preventive measures that may be imple-ented to ensure the safety of the surgical staff during pro-

edures involving intraoperative fluoroscopy, it is importanto identify the multiple sources of X-rays that frequently con-ribute to their exposure. Leakage refers to the small quantityf radiation that escapes through the shielding of the X-rayube. Primary scatter is released once the beam strikes theatient, while secondary scatter is produced as the X-raysollide with other surrounding objects. The sum of thesehree distinct components is known as stray radiation, withhe majority of this occupational exposure arising from pri-ary scatter, which usually exhibits only 0.1-0.2% of the

nergy exhibited by the original beam (Fig. 1).3

ollimationailure to confine the beam area so that it only includes theertinent anatomic structures may give rise to an excessively

arge X-ray field, which increases the amount of radiation thats transmitted throughout the operating room. As noted pre-iously, collimation enhances image contrast by decreasinghe amount of scattered radiation. Nevertheless, it appears asf this protective effect may not be as pronounced for theurgeon as it is for the patient.3

ocation of the Beamhe plane along which the patient is irradiated may also affect

he dose of the surgeon. If the image intensifier is positionedo that the beam passes through the sterile field in closeroximity to the operating room personnel, their exposuresill increase because the scattered X-rays that are generatedill have experienced less attenuation from the patient’s tis-

ues (Fig. 2).3

istances with patients, maximizing the distance between the sur-ical team and the C-arm remains one of the most practical

igure 1 Sources of radiation that contribute to surgeon exposure.3

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Techniques to minimize intraoperative radiation exposure 183

olutions for lowering the amounts of radiation that they areubjected to during these cases. The inverse square law dic-ates that doubling the space that separates an individualrom the beam source reduces the exposure by 25%.4 Basedn these calculations, the National Council on Radiation Pro-ection and Measurements recommends that staff membersho are not working in the operative field should stand at

east 6 feet away from the X-ray tube.5

eam-on Timeot surprisingly, the dose of the surgeon is also directlyroportional to the duration that the fluoroscope is in use.hus, employing these units judiciously and minimizing

heir time of activation may bring about significant improve-ents in the exposures of both the patient and the surgeon.3

odeany of the newer C-arm designs offer a high-level output

eature that renders images with less interference by elevatinghe dose rate of the emitted radiation, which would be ex-ected to increase the exposures of every individual present

n the operating room. However, this option should bevoided unless absolutely necessary because the quantity ofcattered X-rays has been shown to decline by approximately0% when lower energy settings are selected.6 Pulsed-modeuoroscopy may also minimize intraoperative irradiation byecreasing the total beam-on time such that the dose rate maye less than 50% of that incurred with continuous visualizationf the anatomy.7 Finally, the number of scattered X-rays that arereated during these procedures may be governed by theanner in which the images are collected and viewed by the

urgeon; for instance, certain cameras (eg, photofluorospotr cinefluorographic devices) and digital recording tech-iques may require greater exposures than other processing

igure 2 Effect of beam location on surgeon exposure. (A) A centraleam location because the radiation undergoes greater attenuationrom the patient’s tissues before striking the surgeon. (B) Placementf the beam more laterally enhances the energy of the scattered-rays, increasing the dose of the surgeon.3

ystems.5 b

ackscattered Radiationhis category of radiation includes the X-rays that are re-ected away from the surface of the skin, which are of rela-ively high intensity because the incident beam has not yeteen attenuated. The operating room staff is particularly sus-eptible to this backscattered radiation when the C-arm isriented in certain positions such as the arrangement inhich the X-ray tube is situated above the patient and the

mage intensifier is below the table. Therefore, every efforthould be made to reverse the gantry so that the receiver isocated superiorly and angled away from the surgeon’s face toeduce the magnitude of this class of radiation (Fig. 3).3

hieldingven with advances in fluoroscopic technology, the cornerstonef contemporary occupational radiation safety protocols contin-es to be the institution of protective shielding, which is placedetween the X-ray source and members of the surgical team.egardless of whether they are fixed, mobile, or worn as anrticle of clothing, these barriers should ideally safeguard theyes, thyroid, abdominal organs, and all other radiosensitivetructures. An insulated booth that segregates any nonessentialersonnel away from the fluoroscope may provide the best de-ense again the hazards of radiation, but in most circumstances,his strategy may not be feasible. Portable lead shields have alsoeen recognized as an effective method for deflecting X-raysway from the individuals standing behind them. Alternatively,pecialized transparent drapes that are suspended from the ceil-ng may also be utilized to surround the fluoroscope duringhese interventions. Moreover, many operating room tables in-orporate various built-in barriers to inhibit the dispersion ofny scattered radiation.3

Protective gear such as aprons, vests, skirts, thyroid barri-rs, and gloves are mandatory for those working in an un-hielded environment. These garments are largely composed

igure 3 Effect of C-arm orientation on backscattered radiation. (A)he amount of X-rays directed toward the surgeon increases when

he X-ray tube is above the patient and the receiver is below theable. (B) Conversely, reversing the gantry and angling the receiverway from the surgeon’s face serves to minimize the amount of

ackscattered radiation that is absorbed.3

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184 R.B. Butler and K.A. Poelstra

f flexible lead-impregnated rubber, which typically rangesn thickness from 0.25 to 1 mm in accordance with the an-icipated exposure of the area that is being covered. Whilereater than 90% of X-rays are attenuated by 0.25 mm of thisaterial, a 0.5-mm layer blocks nearly 99% of the radiation

hat is encountered but weighs twice as much as the thinnerown.4 Similarly, thyroid guards that are at least 0.5 mmhick have been shown to decrease the dose administered tohe neck by at least 90%. Goggles are also available, whichay impede between 20 and 70% of the X-rays targeting the

yes, depending on the quantity of lead that they contain. It ismportant that any individual whose back is likely to becomexposed to radiation during the course of these proceduresonsider wearing barrier protection that completely encloseshe trunk region, eg, wraparound aprons.3 Without excep-ion, every piece of apparel should be periodically examinedo confirm that the integrity of its shielding is still intact.

Ironically, the use of sterile radiation-resistant gloves rein-orced with either lead or tungsten has actually been found toncrease the exposure of the surgeon. Wagner and Mulherneported significant variation in the shielding properties ofhese types of gloves and concluded that any additional pro-ection they imparted was offset by the generation of greateruantities of scattered electrons, which subsequently ampli-ed the effective dose applied to the hands by 15%.8 Theuthors also caution that by establishing a false sense of se-urity, this practice may encourage surgeons to insert theirands directly in the fluoroscopic beam, which would lead toven further irradiation of their extremities.

onitoringurgical personnel whose potential radiation exposures rep-esent at least 10% of the recommended maximum limitust be furnished with dosimeters, which record the quan-

ities of X-rays that they are subjected to over a specifiedength of time. The data registered by a dosimeter is an officialocument that may even have legal implications. Close mon-

toring of the cumulative doses of the surgeon and the oper-ting room staff is critical for assessing the reliability of thexisting safety provisions and determining whether any otherhanges in technique are warranted to minimize the risks ofxcessive radiation exposure.

As with protective shielding, the fluoroscopic equipmenthould also be regularly inspected so that any required mainte-ance may be performed in an expedient fashion. When thefficiency of a C-arm declines beyond a certain point, the auto-atic brightness control function compensates for the poorer

uality of the images by boosting the intensity of the incipienteam, which gives rise to higher exposure rates; similarly, anyeterioration of the insulation that lines the X-ray tube mayesult in greater leakage of radiation from the housing apparatus.

urgeon-Directedanagement of the Fluoroscopic Beam

oordeen and coworkers calculated the dose discrepancieshat may occur as a result of the specific method by which the

uoroscope is activated.9 Orthopedic trauma surgeons who

perated the unit themselves by manually depressing a footedal were exposed to significantly less X-rays than those whoeded control of the C-arm to a radiology technician (P � 0.05).hese findings suggest that surgeon-directed regulation of thisrocess may yield shorter beam-on times and reduced occupa-ional exposures.

uture Directionshe use of fluoroscopy during spinal procedures will likely con-

inue to rise, especially with the advent of minimally invasiveurgical approaches such as the insertion of percutaneous pedi-le screws. The success of these interventions is largely predi-ated on the acquisition of high-resolution intraoperative im-ges, which in most cases are obtained with a conventional-arm. To circumvent many of the disadvantages inherent to

raditional fluoroscopic techniques including the obligatory ex-osure of the patient and surgeon to variable amounts of X-rays,everal different innovative imaging modalities have been devel-ped to enhance the safety and efficacy of multiple orthopedicnd neurosurgical applications. The majority of these devicesay also be coupled with computer-assisted image guidanceortals to facilitate surgical navigation. In addition to improvinghe accuracy of spinal instrumentation, these strategies have alsoeen reported to decrease the radiation doses associated withhese operations.10,11 Although a detailed discussion of thesetudies is beyond the scope of this review, many of these novelystems for depicting surgical anatomy will be examined else-here in this issue.

ummaryhe deleterious health effects that may be precipitated byxcessive intraoperative radiation are well documented in theiterature, so it is imperative that every attempt be made to

inimize the doses that are absorbed by the patient andurgeon during spinal procedures that require C-arm imag-ng. Surgeons must not only be cognizant of the currentadiation safety guidelines and the preventive measures thatomprise the standard of care, but they also have a responsi-ility to address any deficiencies in technique that may sub-

ect these individuals to needless radiation. Furthermore, alter-ative methods for visualizing spinal structures are expected toecome a reality in the near future, which may facilitate evenreater reductions in the number of X-rays that are emitted inhe operating room setting.

eferences1. ParryRA,GlazeSA,ArcherBR:TheAAPM/RSNAphysics tutorial for residents:

typicalpatient radiationdoses indiagnostic radiology.Radiographics19:1289-1302, 1999

2. Wagner LK, Archer BR: Minimizing risks from fluoroscopic x-rays (ed 2).Houston, TX, Partners in Radiation Management, 1998

3. Brateman L: The AAPM/RSNA physics tutorial for residents: radiationsafety considerations for diagnostic radiology personnel. Radiographics

19:1037-1055, 1999

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Techniques to minimize intraoperative radiation exposure 185

4. Bushberg JT, Seibert JA, Leidholdt EM Jr, et al: The Essential Physics ofMedical Imaging. Baltimore, MD, Williams & Wilkins, 1994, pp 583-632

5. National Council on Radiation Protecting and Measurements. Qualityassurance for diagnostic imaging. NCRP report no. 99. Bethesda, MD,NCRP, 1988

6. FluoroScan mini C-arm unit. Health Devices 24:44-70, 19957. Strauss KJ: Cardiac catheterization equipment requirements: pediatric

catheterization laboratory consideration, in Nickoloff EL, Strauss KJ(eds): Categorical Course in Diagnostic Radiology Physics: CardiacCatheterization Imaging. Oak Brook, IL, Radiological Society of North

America, 1998, pp 105-119

8. Wagner LK, Mulhern OR: Radiation attenuating surgical gloves: effectsof scatter and secondary electron production. Radiology 200:45-48,1996

9. Noordeen MH, Shergill N, Twyman RS, et al: Hazard of ionizing radi-ation to trauma surgeons: reducing the risk. Injury 24:562-564, 1993

0. Jones DP, Robertson PA, Lunt B, et al: Radiation exposure during flu-oroscopically assisted pedicle screw insertion in the lumbar spine.Spine 25:1538-1541, 2000

1. Gebhard FT, Kraus MD, Schneider E, et al: Does computer-assistedspine surgery reduce intraoperative radiation dose? Spine 31:2024-

2027, 2006