Safety of Fluoroscopy in Patient, Operator, and Technician

Function

X-Ray Basics, Design and Function

The basics of the C-arm fluoroscopic machine include an X-ray tube mounted below an image intensifier which is connected via a supportive C arm-shaped structure, hence its name. This allows for the apparatus to be situated directly above the patient and generate accurate anatomic images. It also allows the imaging apparatus to be mobile and easily change positions, facilitating its functionality in a fluoroscopic suite. Providers may obtain necessary views in any anatomic plane in a relatively simple manner. Ionizing radiation is utilized to generate a functional image in real-time during fluoroscopic procedures to guide diagnostic and therapeutic intervention.

An electrical current is used to generate X-rays from the X-ray tube via the creation of electrons directed at a tungsten anode which then converts the electrical energy and emits X-rays.[2][3] This electrical energy can be modified before X-ray transmission via adjustments to the current or voltage potential across the cathode and anode in the X-ray tube to optimize the image generated. Increasing adjustments to the voltage potential (kVp) will ultimately deliver X-rays of a higher energy level, which allows for deeper penetration of tissue. In contrast, the number of X-ray emissions stays relatively stable.

However, increasing amperage (mA) darkens the image and improves contrast but directly correlates with X-ray production and subsequent exposure.[2][3] Ideal settings for image generation with minimal increase in scatter radiation, therefore, consist of moderate voltage with a minimal current, automatically calibrated via the automatic exposure control (AEC) function. When used at the low dose rate, the AEC function will automatically optimize kVp before making adjustments to the mA to generate the highest image quality with optimal exposure while simultaneously limiting the total radiation dose delivered.[2]

Radiation exposure comes from 3 major sources in the fluoroscopic suite, including the primary X-ray beam and leakage and scattered X-ray beams.[4] As X-rays travel from the source toward the patient, many of the particles do not make it to the image detector as they are either absorbed, attenuated, or scattered.[3] X-ray particles that traverse through the patient unaffected reach the image intensifier and are directly utilized in image acquisition. Those that lead to incoherent scattering are most concerning healthcare providers as they contribute most to occupational radiation exposure.[5] While air molecules can serve as a source of scattering, radiation is primarily scattered by patient atoms. Incoherently scattered X-ray photons are those which are emitted after primary X-ray particles interact with patient atoms and lead to the generation of new photon emissions, which occur in a random direction, making them most hazardous to healthcare personnel. Therefore, the entire radiologic suite is considered a potential risk for significant radiation exposure, not simply the path of the primary beam. 

Manufacturers are aware of the elevated risk of exposure to harmful emitted X-rays and have considered this during the development of their machinery. Several mechanisms and structural designs exist to help decrease the risk of exposure. For example, the primary X-ray beam is relatively focused and controlled off of the tungsten anode from which it is emitted since the anode is properly angulated and positioned. However, to further control and direct the primary beam, metal filters usually made of either copper or aluminum are utilized to absorb low-frequency X-rays before exiting the X-ray tube.[3] These low-frequency X-rays contribute little to image production but greatly affect radiation exposure; therefore are ideally absorbed to prevent unnecessary hazardous exposure.

Collimation is also utilized to design the X-ray fluoroscopic machine, which helps to narrow and direct the primary X-ray beam out of the X-ray tube, usually via an iris-shaped lens. This decreases the amount of patient tissue exposed to scattered radiation, decreases occupational exposure to scattered radiation to healthcare personnel, and improves image quality.[2] Mounted to the X-ray tube is a separator cone, which serves as a barrier to prevent the patient's position from exceeding the minimum distance needed between the X-ray source and the patient skin. This serves to help protect patients from acute radiative skin injuries. Another design feature includes anti-scatter grids on the image intensifier, which decrease the amount of scattered radiation that reaches the entrance phosphor and ultimately increases image quality. However, when the anti-scatter grids are in place, it greatly increases the amount of radiation exposure required to generate an image. Therefore, it is ideally removed when conditions for scattering are low to decrease the amount of radiation delivered ultimately.[2]

Issues of Concern

Radiation Protective Measures 

In general, ALARA or as low as reasonably achievable fundamentally guides practitioners in the use of ionizing radiation as it is generally accepted that there is some associated risk with any amount of radiation exposure, no matter how small. Therefore, training and education of healthcare personnel who utilize fluoroscopy are paramount for the safety of the patient and those who work in fluoroscopy settings such as radiation technicians, nursing, and assisting providers as many acute radiation-related injuries are deemed preventable with proper technique, awareness, and training.[6] This includes training in proper technique, a fundamental understanding of the basics of ionizing radiation, and the possible acute complications, including radiation dermatitis, epilation, and burns, so that patients may be correctly counseled on the implications and risk before their procedure.[6] Other techniques such as minimizing magnification, avoiding continuous beam on imaging, proper positioning, and appropriate collimation would be integral in an appropriate radiation curriculum. This training and safety credentialing would also be specialty-specific as radiation implementation varies greatly depending on the medical procedure being performed according to different risk profiles. 

To further decrease radiation exposure, three guiding principles are time, distance, and shielding.[7] Radiation exposure is cumulative in nature. Hence, no radiation exposure is considered to be "safe," and current studies continue to help elucidate long-term side effects. Therefore, the exposure time must be limited and monitored to track progression over time. Several tactics to decrease time exposed include utilizing pulsed and low dose image generating modes over continuous or cine modes, utilizing ultrasound over fluoroscopy whenever appropriate, and monitoring annual maximum permissible radiation dose usually via dosimetry.[7]

Dosimeters are easily implemented, cost-effective, and can increase the awareness of providers about their personal radiation exposure. Education of providers who utilize ionizing radiation in terms of maximal annual permissible radiation doses should be known and readily available to practicing providers and healthcare workers so that it may be compared to actual, measured exposure doses to keep exposure as low as possible. The Sievert (Sv) serves as the SI unit of measurement for radiation exposure. As recommended by the International Commission on Radiologic Protection (ICRP), total body dose should not exceed 20 mSv annually, extremities are limited to 500 mSv per year and lens of the eye 150 mSv per year while the European Atomic Energy Community limits exposure to the lens to 20 mSv annually.[8] It should also be noted that image quality, while important, does not have to be held to a standard of perfection. The goal for image acquisition in fluoroscopy is a functional image, as striving for perfection subjects the patient and providers to unnecessary radiation. 

Distance is likely the most important variable to control as it may be the most effective means to decreasing exposure since radiation intensity rapidly falls with increasing distance.[7] According to the inverse square law, as the distance from the radiation source is doubled, radiation exposure is inherently decreased by a factor of 1/4. Additionally, this principle also helps guide the positioning of personnel within the radiology suite alongside appropriate planning, communication, and team dynamics. Patient positioning is also optimized to minimize radiation exposure to the patient, which also serves to decrease the amount of scattering to healthcare workers by maximizing the distance between the table and the radiation source and placing the patient as close to the detector as possible.[9] While oftentimes practitioners are situated directly adjacent to the patient due to the need for access, proper positioning away from the X-ray source during the acquisition of lateral and oblique imaging is ideal. Therefore, it is recommended that healthcare workers stand on the side of the image detector and not on the side of the X-ray tube, which serves as a direct source of radiation exposure whenever applicable.

Protective lead shielding is an effective means of protection against radiation exposure, especially to sensitive tissues such as the thyroid gland, gonads, bone marrow, and lens of the eye. Hence the need for protective garments such as aprons, thyroid shields, caps, and lead glasses during fluoroscopic procedures. Lead aprons of the wrap-around, vest type variant are superior to non-vest type aprons due to their adequate coverage of the posterior aspect of the provider and a double layer of lead equivalence in the anterior aspect.[10] Furthermore, mounted or mobile lead shielding devices can be utilized to further decrease radiation exposure in addition to wearable lead protective devices in the form of tableside drapes, ceiling-mounted shields, and mobile barriers made of lead oxide. Modern-day practice commonly employs non-lead aprons as they are lighter, which improves ergonomics, tolerance, and compliance during long procedures and the added benefit of being non-toxic in the case of accidental exposure.[11] A lead equivalence of 0.35 mm is highly effective and has been shown to decrease exposure by up to 90%.[8] 

Shielding of the patient also helps decrease the amount of radiation delivered and the total amount of radiation scatter and subsequent occupational exposure. As the lens of the eye is one of the most sensitive tissues to radiation damage, protective eyewear is of the utmost importance. The risk of radiation-induced cataracts is cumulative in nature and has been shown to specifically damage the posterior subcapsular region of the lens.[12] However, it is one of the most overlooked pieces of protective equipment with some of the lowest adherence rates in radiologic suites.[9] The hands of the working provider are subject to high amounts of scatter radiation as well as the possible risk of entering the field of the primary beam. Protective gloves have shown limited benefit as optimizing technique and minimizing imaging while the hands of the provider are exposed to the field serves to decrease radiation exposure more effectively.

Clinical Significance

Biological Effects of Radiation

While it is relatively known and accepted that radiation exposure leads to an increased risk of adverse events in a cumulative fashion, much remains unclear about the long-term health effects of low-dose radiation exposure and requires further studies for elucidation.[8] Radiation effects are both deterministic as well as stochastic in nature. Stochastic effects of exposure include carcinogenesis, cataractogenesis, and hereditary effects, which are dose-independent and typically have a longer latency period than deterministic effects. These effects are secondary to free radical damage to DNA. Deterministic effects, also known as tissue effects, are dose-dependent and occur after a specific threshold of radiation exposure, including radiation dermatitis, skin necrosis, and hair loss.[12] Radiation protective measures have played an integral role to further occupational and patient safety. While some aspects of risk remain unclear, the education and promotion of radiation safety remain a top priority among healthcare facilities and personnel.

Enhancing Healthcare Team Outcomes

The protection of patients and healthcare personnel against radiation exposure requires an interdisciplinary team approach with the guidance and input of multiple interprofessional team members. Implementation of a radiation safety program is ideal as all team members are subject to similar training and are educated on regulations and safety measures, increasing awareness among personnel providing radiologic services to patients to ultimately improve patient safety. All healthcare personnel should be trained in the potential negative outcomes of acute radiation exposure to increase awareness for potential complications such as dermatitis, skin necrosis, erythema, and hair loss.

Radiation safety programs are also ideally designed by a multidisciplinary team consisting of radiation biologists, medical physicists, and radiologists. Further measures include establishing strong lines of communication among team members to facilitate safe imaging, such as ensuring the minimal amount of personnel necessary is present to avoid unnecessary exposure and communicating beam-on time in busy settings. Radiation safety protocols utilize small retrospective cohort studies to help generate guidelines and estimate risk. However, a need for further larger prospective studies is necessary to help clarify the long-term harmful effects of low-dose occupational radiation exposure to help further generate safety measures.[12] [Level 3]