In parallel with advances in minimally invasive spinal techniques and endovascular neurosurgical procedures, radiation use for diagnostic and therapeutic purposes has increased. Concerns have been raised about radiation side effects and long-term complications, particularly in the operator and exposed personnel. Radiation use during procedures has increased in conjunction with an increase in minimally invasive image-guided surgery. In this review, the current literature regarding risks of radiation exposure to the personnel involved in radiation-based procedures and strategies to reduce these risks are summarized. Current standards in radiation risk reduction and specific techniques that can minimize radiation exposure are also discussed.
Key points
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Increased radiation exposure is largely due to increased used of radiation for therapeutic and diagnostic purposes.
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Minimizing radiation exposure can be achieved by controlling radiation doses, limiting time of exposure, maintaining distance from the source, shielding, and appropriate engineering.
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Minimally invasive spinal surgery is associated with high levels of radiation exposure, which warrants abiding by radiation exposure precautions.
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Cone beam computed tomography reduces the surgeon’s exposure while increasing the patient exposure.
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Neuronavigation is an increasingly popular radiation-free technique, which can be used in certain cases of minimally invasive spinal procedures.
Introduction
Radiation use for diagnostic and therapeutic purposes has significantly increased over the past several decades. Techniques that rely on radiation for image guidance such as minimally invasive spine surgery and neurointerventional surgery have resulted in less morbidity and improved outcomes for select patients, but the issue of operator and personnel exposure remains a concern. Protective technologies and policies continue to evolve to meet the protection needs. Incorporating these policies and technologies into practice is a challenge.
In light of the available data regarding radiation exposure, national and international organizations have recognized radiation risk from occupational exposure as a significant hazard to health care professionals. Particularly in specialties such as spine surgery and neurointerventional surgery, operators who are susceptible to increased radiation exposure consider that the large number of procedures they perform can benefit from other experiences in the operative field or the angiography suite. Knowledge acquired in one field or the other can help promote radiation safety among neurosurgeons in general and make the operative setting a safer environment for the patient, the surgeon, and the operating room (OR) personnel ( Box 1 ).
Wear protective devices (lead apron, thyroid shield, leaded glasses, leaded gloves)
Use the hands-off technique
Keep X-ray tube under the patient table
Use time-distance-shielding principle: minimize time, maximize distance, use shielding
Stand by the detector opposite to the X-ray source
Wear dosimeter
Use fluoroscope in automatic mode
Establish a radiation exposure profile of your operating room and take advantage of the room design when feasible
Use shielding even when using cone beam computed tomography scan
Beware of a false sense of safety while wearing protective equipment
Introduction
Radiation use for diagnostic and therapeutic purposes has significantly increased over the past several decades. Techniques that rely on radiation for image guidance such as minimally invasive spine surgery and neurointerventional surgery have resulted in less morbidity and improved outcomes for select patients, but the issue of operator and personnel exposure remains a concern. Protective technologies and policies continue to evolve to meet the protection needs. Incorporating these policies and technologies into practice is a challenge.
In light of the available data regarding radiation exposure, national and international organizations have recognized radiation risk from occupational exposure as a significant hazard to health care professionals. Particularly in specialties such as spine surgery and neurointerventional surgery, operators who are susceptible to increased radiation exposure consider that the large number of procedures they perform can benefit from other experiences in the operative field or the angiography suite. Knowledge acquired in one field or the other can help promote radiation safety among neurosurgeons in general and make the operative setting a safer environment for the patient, the surgeon, and the operating room (OR) personnel ( Box 1 ).
Wear protective devices (lead apron, thyroid shield, leaded glasses, leaded gloves)
Use the hands-off technique
Keep X-ray tube under the patient table
Use time-distance-shielding principle: minimize time, maximize distance, use shielding
Stand by the detector opposite to the X-ray source
Wear dosimeter
Use fluoroscope in automatic mode
Establish a radiation exposure profile of your operating room and take advantage of the room design when feasible
Use shielding even when using cone beam computed tomography scan
Beware of a false sense of safety while wearing protective equipment
Regulatory processes in radiation protection
An increasing number of radiation-related procedures as well as an increasing number of involved personnel led to the institution of federal and international regulations aiming to control radiation exposure. As a result of international collaboration, the International Commission on Radiological Protection issued the As Low As Reasonably Achievable (ALARA) principle, which is a regulatory requirement aiming to minimize radiation exposure by using all reasonable methods. All operators using ionizing radiation are advised to abide by this principle.
Key concepts in radiation physics
Radiation comprises energetic particles or energy waves traveling in space. When these particles or waves have enough energy to liberate electrons from atoms or molecules, this is known as ionizing radiation. Radiation propagates in a forward linear direction in air. At the air-matter interface, physical phenomena such as absorption, reflection, refraction, and scattering may occur, possibly leading to secondary sources of radiation. Many variables can be used to quantify radiation exposure. The most common methods of measuring radiation in medicine include absorbed dose and equivalent dose, which are measured in Gray and Sievert, respectively. One Gray and 1 Sievert both correspond to the absorption of 1 J of energy per kilogram of matter. However, the Sievert is corrected to express the equivalent dose for a fixed mass of biological tissue.
Biological effects of radiation
Ionizing radiation damages cells by incurring direct injuries to DNA molecules or by inducing free radicals, which may affect DNA as well as other cellular structures. Low-dose radiation is usually believed to cause stochastic effects such as mutations, which may result in cancer, and hereditary diseases. However, data regarding low-dose radiation exposure remain limited because most low-dose human ionizing radiation risk estimates come from studies conducted on atomic bomb survivors in Japan.
Large doses of radiation might also cause stochastic effects; however, they are more likely to induce direct necrosis or fibrotic changes. Documented radiation effects range from skin irritation to instantaneous death. Mild radiation sickness necessitates a dose that is 10 times higher than US radiation workers’ annual limit. Organs that are particularly sensitive to radiation include skin, the eyes, and most mucosal membranes. Acute radiation doses delivered to skin during a single procedure or closely spaced procedures may induce skin erythema at a dose of 2 Gy, permanent epilation at a dose of 7 Gy, and delayed skin necrosis at 12 Gy. Secondary ulceration may occur at 24 Gy. Eye exposure may cause cataract if 2 Gy of radiation is received in a short period or if 4 Gy is received in less than 3 months. Cataract may occur as a delayed effect if 5.5 Gy is received in more than 3 months.
Sources of radiation
In its 2008 report to the United Nations General Assembly, the United Nations Scientific Committee on the Effects of Atomic Radiation classified radiation exposure into 2 major types: public exposure and occupational exposure. Public exposures were divided into those resulting from natural sources such as cosmic radiation, man-made sources such as nuclear power production, historical situations, and exposure from accidents. Occupational exposures were divided into natural sources such as cosmic ray exposures of aircrew or space crew and man-made sources such as medical uses of radiation.
General recommendations for minimizing radiation exposure
In light of the increased use of radiation in daily medical practice, abiding by the ALARA principle has become mandatory. Observing this principle entails applying several strategies to limit radiation exposure.
Controlling Radiation Doses
Radiation dose received by a biological tissue is the major determinant of histopathologic outcomes. Therefore, controlling radiation doses is the most important step in the process of avoiding side effects. This process can be achieved via optimizing image capturing algorithms and avoiding unnecessary radiographic studies. For example, new fluoroscopy algorithms are optimized to benefit from the evolution of detectors, which diminishes the amount of radiation needed without compromising the clinical sensitivity or specificity of the study.
A good planning of radiographic shots can help control doses of radiation by minimizing the number of unnecessary shots. For example, fluoroscopy technicians should make sure they have an adequate setting before taking the shot, thus minimizing the number of repeated unnecessary exposures. Ideally, only 1 shot would be taken per procedure step. In deformity cases, radiation doses can be controlled via preoperative planning, resulting in fewer radiographs taken during the surgery.
Limiting Time of Exposure
Another factor that correlates with the absorbed dose is the time of exposure. Limiting exposure time depends on good operator training and also on limiting the number of shots taken during the procedure. Exposure time is particularly important in fluoroscopic procedures; certain procedures such as coiling necessitate videolike image acquisition. Operators of fluoroscopic machines, whether in the OR or in the interventional suite, should try to take the least number of views to minimize exposure.
Time of exposure can also be limited by stepping out of the room or standing behind a shield when feasible. For example, during neurointerventional surgery, an automatic drug delivery system, which can inject contrast at preset rates, allows the personnel to step out of the room while the angiogram is being performed. Although this strategy might not be a possibility when an aneurysm is being coiled, avoiding unnecessary radiation during simple angiograms might significantly limit the total exposure time.
Time of exposure can also be analyzed from the larger perspective of lifetime exposure. From this perspective, it is the role of regulatory authorities to ensure that lifetime exposure of health care professionals does not exceed maximal allowed doses.
Maintaining Distance from Source of Radiation
Energy carried by radiation per unit surface is inversely proportional to the square of the distance traveled between the source and the detector. This finding means that energy carried by radiation decreases rapidly with distance from the source. Therefore, maintaining distance from the source helps achieve better radiation protection. In addition to attenuation caused by the distance, air between the source and the operator or the patient can also provide minimal shielding, which helps decrease the energy of radiation. Consequently, maximizing the distance between the source and the operator, the patient, or the personnel, when feasible, can help reduce the amount of radiation received. Although there is no agreement on how much distance is enough, from a physics point of view, even minimal distances can significantly affect radiation exposure.
This goal can also be achieved by stepping out of the room or by stepping back from the radiation field during spine surgeries. Other minor steps that can be taken include using a Kocher to hold the Jamshidi needle as seen in Fig. 1 .
Shielding
Shielding minimizes radiation exposure by ensuring that radiation is absorbed before it reaches sensitive biological tissue. Shielding depends both on the physical nature of the offending particle and the shield. For example, whereas for α particles keratin on top of the skin provides enough shielding, γ rays necessitate dense metallic shielding such as lead. Dense metal shields, such as lead, provide more efficient shielding than other types of shields, such as glass. For this purpose, leaded transparent materials have been developed and are available for use in protective eyewear and mobile shields. Shielding also depends on the shield thickness; when an energetic particle is traveling through a shield, it is more likely to be absorbed when the lead is thick enough. Shielding types and their uses are discussed later.
Collimation
Whereas shielding consists of blocking radiation before it reaches the physician, collimation consists of blocking radiation before going out of the source. Collimation can be performed when the operator does not need to visualize the whole field and has been shown to significantly decrease radiation exposure. A recent study also showed that collimation maintains image quality. Collimation is available in most modern machines and is beneficial to both the patient and the surgeon. Collimation can prove particularly beneficial in interventional neurosurgery. For example, during coiling, the surgeon can minimize radiation exposure by collimating the field to view the aneurysm and nearby vessels.
Engineering Controls
ORs as well as neurointerventional suites can be customized to minimize radiation exposure from secondary sources. From the design of facilities and equipment to the room setup, minimizing scattering as well as minimizing reflections are engineering challenges that can optimize this environment for use of radiation for medical purposes. This situation is achieved by abiding to several engineering principles: first, increasing absorbing surfaces to minimize reflections or scattering; second, making free space available to ensure the possibility of fitting mobile shields; and third, by providing roof-suspended radiation shields.
Radiation exposure to the operator
There are 3 sources of radiation exposure to the operator: primary beam exposure, scattered radiation from the patient, and X-ray tube leakage. The beam of radiation is most intense on the side entering the patient and significantly decreased on the image receptor side of the patient. Scattered radiation is a result of X-ray beam interactions with patient tissues. These Compton interactions are greatest near the beam entrance and lower on the exiting side of the patient, because most of the radiation is absorbed by the patient. The image receptor (image intensifier [C-arm unit] or digital image detector [neurointerventional suite]) contains lead shielding to act as a barrier for both primary and scattered radiation. Hence, it is advisable that operators work on the image receptor side whenever possible to decrease exposure. In addition, using collimators to exclude the operators’ hands/fingers from the radiation beam can also reduce exposure.
Even although there is protective lead lining the X-ray tubes, radiation leakage is a known occurrence in fluoroscopy units in which radiation emanates not only in the primary beam but also in other directions. Therefore, routine maintenance is mandatory to evaluate for and minimize any tube leaks.
Operators should keep track of radiation exposure with the use of thermoluminescent dosimetry badges, typically worn at the waist level under the apron and at the thyroid level over the lead shield. The International Commission on Radiological Protection recommends that the effective dose be limited to 20 mSv/y averaged over 5 consecutive years, with no single year exceeding 50 mSv.
Radiation exposure to the patient
X-ray tube voltage and current, automatic brightness control (ABC), collimation, beam filtration, use of pulsed fluoroscopy mode, and magnification are various parameters of the fluoroscopy unit that affect radiation dose to the patient. The voltage (kVp) and current (mA) are controlled by the ABC subsystem to produce enough radiation to produce an acceptable image at the image receptor (typically 60–120 kVp). The patient dose is directly proportional to the tube current and beam-on time. The former is out of the operator’s control, for the most part. However, the total beam-on time can be controlled by the operator and should be minimized as practically possible.
Collimators allow operators to focus in on the area of interest and reduce radiation exposure to the areas that are not of clinical interest. As mentioned earlier, collimation also decreases operators’ exposure to scatter radiation. The interventional units are also equipped with equalization filters, more commonly known as soft cones, which are lead-impregnated acrylic or rubber filters, which reduce patient dose.
Beam filters are thin metal (aluminum or copper) filters, which are located between the exit port and collimator. These filters reduce patient dose by absorbing low-energy X-rays that are insufficient to penetrate the patient and thus are not useful in image production.
Pulsed fluoroscopy mode, found on more recent interventional units, has decreased patient and operator radiation doses. Instead of producing X-rays continuously, the X-ray tube is pulsed on for several milliseconds and then turned off until the next frame is acquired. Lowering the frame rate helps reduce radiation dose, although at the expense of temporal resolution.
Although magnification helps sort out minute details, it does so at the expense of higher patient dose. With increased magnification, the total brightness gain decreases and the resulting image is dimmer. The ABC subsystem compensates for this situation by increasing the patient entrance dose. Therefore, the magnification function should be used when it is absolutely necessary.
Current practices in radiation protection
Various devices were developed to minimize radiation exposure and ensure a safe environment for both the operator and the patient. The armamentarium includes aprons, thyroid shields, eyewear, and protective gloves, as well as mobile shields.
Lead Aprons
Protective shielding is essential and should be mandatory when X-ray units are in function. Protective aprons typically consist of 0.5 mm of lead or lighter-weight lead equivalent material; thicknesses ranging from 0.25 to 1 mm lead equivalent are available. A 0.5-mm lead equivalent usually attenuates 90% of the radiation that strikes it. Various lead apron styles exist on the market, including a wrap-around style consisting of a skirt and vest, front coverage aprons, and aprons that wrap around the body. The advantage of the vest and kilt garment is that is allows the weight to be distributed to the hips, instead of concentrated to the upper back. Lead aprons should be fitted to the individual so that there are no gaps in appropriate coverage ( Fig. 2 ). Shielding material should be scanned under fluoroscopy on a yearly basis to scan for holes and reduced shielding integrity.
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