Radiation Safety and Protection in the Interventional Fluoroscopy Environment

M. Victoria Marx

Over the last 25 years, fluoroscopically guided interventional procedures have revolutionized medical care. Percutaneous stent placement has replaced surgical bypass for arterial revascularization. Surgical decompression of portal hypertension is rarely performed because of the efficacy of transjugular intrahepatic portosystemic shunt (TIPS) procedures. Hysterectomy for symptomatic fibroids is becoming less common as a result of the wide availability of uterine artery embolization. These developments have benefited thousands upon thousands of people because of less morbidity than in the surgical procedures they have replaced.

Fluoroscopy does, however, come with a price: exposure to ionizing radiation. It is the responsibility of each interventionalist to use fluoroscopy judiciously and in such a way that its immediate medical benefits outweigh its potential future risks. To do so, the practitioner must understand the bioeffects of ionizing radiation, provide meticulous preprocedural and postprocedural patient care, and develop optimal work habits in the fluoroscopic suite. A well-rounded radiation management program is important not only to minimize exposure to the patient but also to minimize occupational doses incurred by the interventional radiology team.

Negative Effects of Ionizing Radiation

Ill effects of radiation can be divided into two basic categories: stochastic effects and deterministic effects.¹ Stochastic effects are those in which no clear relationship exists between the magnitude of the radiation dose and the severity of the effect. Stochastic effects include genetic mutation and induction of cancer. Estimations of the incidence of stochastic effects have been based on a no-threshold linear model assumption from the effects identified as a result of the atomic bomb detonations during World War II. These assumptions are not universally accepted. However, because of this uncertainty, the current approach is that stochastic effects have no threshold dose. Therefore, no radiation dose can be considered absolutely safe. It is imperative that fluoroscopically guided diagnostic and therapeutic procedures be performed under the safest conditions possible.

Deterministic effects are those in which the likelihood and severity of the effect are related to the magnitude of the radiation dose: the higher the dose, the more severe the effect. Deterministic effects have a minimum dose threshold below which no effect will occur. Examples of deterministic effects are radiation-induced skin injury (including epilation, acute burns, and delayed ulcers) and radiation-induced cataracts. The threshold dose for temporary epilation is about 3 Gy, whereas that for development of a cataract is about 2 Gy for a single exposure. Thresholds are higher for doses fractionated over time. Cataracts and epilation have occurred in patients as a consequence of complex intracranial neurointerventional procedures such as embolization of arteriovenous malformations (AVMs).

Since the mid-1980s, skin injuries have been reported in patients as a direct result of complex fluoroscopically guided interventional procedures, including arterial embolization, arterial revascularization, cardiac radiofrequency ablation, and TIPS.² The rise in reporting these adverse events resulted in U.S. Food and Drug Administration (FDA) action in 1994³ and in U.S. federal regulations limiting the x-ray tube output of interventional fluoroscopic equipment. Similar actions have taken place throughout the world.

The threshold dose for acute skin erythema is about 2 Gy, and that for delayed deep skin ulcers is about 12 to 15 Gy. The risk for deterministic injury rises if multiple sequential procedures are performed at the same anatomic location (i.e., a TIPS procedure and TIPS revision 3 months apart). Other risk factors for skin injury include obesity, diabetes mellitus, and connective tissue disease.⁴ Minimizing the risk of deterministic patient injury is a major focus of current radiation safety initiatives.

Management of Patient Exposure

Equipment Purchase and Maintenance

Optimal radiation exposure management begins with equipment purchase and room design. The interventionalist must be involved in both processes and must insist that radiation safety be a major factor in decision making. For an existing interventional radiology suite, adherence to a preventive maintenance schedule ensures that equipment will operate properly. Preventive maintenance also allows early replacement of parts before their deterioration contributes to unnecessarily high radiation exposure.

Preprocedural Patient Care

The interventional procedure must be medically necessary to justify exposure to ionizing radiation. This is particularly important for procedures known to be associated with high exposure: TIPS, visceral stent placement, visceral embolization, and neuroembolization.⁵ For these interventions in particular, the risk for radiation-induced skin injury should be specifically discussed in the consent process. In addition, history taking should include questions about previous radiation exposure and factors that increase a person’s susceptibility to radiation-related skin injury (e.g., diabetes). The physical examination should include inspection of the skin at previous x-ray beam entry sites.

Discussion of radiation-induced cancer risk is not typically included in the consent process because the immediate benefit of a medically necessary procedure far outweighs the risk for development of cancer in the distant future. However, the interventionalist should be prepared for patient questions regarding this issue. Discussion can include a review of the medical benefits of the planned procedure, a comparison between the relatively high overall risk for cancer in the general population and the small incremental risk engendered by medical radiation exposure, and mention of the long latent period between exposure and induction of cancer for most tumors.

Patient pregnancy is a contraindication to fluoroscopically guided procedures because of the risk of genetic mutation during early gestation and the risk of mental retardation and leukemia during late gestation. Because the life of the fetus depends on the life of the mother, however, occasional exceptions to this rule exist, particularly in the setting of acute trauma management. It is key for the interventionalist to collaborate closely with an obstetrician and a physicist during and after the procedure. In instances in which the woman and fetus survive the acute threat to life, formal fetal dose calculation may contribute to a recommendation that the pregnancy be terminated. The same collaboration should take place if it is found after the fact that a fetus was exposed unintentionally.

Intraprocedural Patient Care

Work habits of the interventionalist have a profound effect on patient radiation exposure.⁶ Optimal work habits require knowledge of radiation physics, familiarity with tableside controls of the x-ray equipment, practice using these controls, and a commitment to radiation safety as a patient care priority.

For most interventional procedures, fluoroscopy time is the single most important determinant of patient radiation exposure that is under control of the operator. It correlates poorly with patient dose, however, because so many other variables, such as body habitus, affect the absorbed dose. It is possible to reach a skin dose of 2 Gy with a fluoroscopy time of 15 to 20 minutes in an obese abdomen. The operator should strive to keep the fluoroscopy time as brief as possible and should maintain awareness of the elapsed fluoroscopy time during the course of a procedure. New interventional rooms display the elapsed fluoroscopy time on an in-room monitor, whereas older equipment uses an audible signal at 5-minute intervals to note the elapsed fluoroscopy time.

Factors affecting fluoroscopy time include complexity of the procedure, operator experience, patient anatomy, image quality, inventory of disposables, and luck. One learned skill that can help lower fluoroscopy time is to make use of last image hold

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