Introduction

Imaging studies that utilize ionizing radiation are essential in the diagnosis and treatment of a variety of urologic conditions. With kidney stone disease increasing worldwide, endourological procedures utilizing fluoroscopy will undoubtedly continue to be performed in increasing numbers. While most radiation generated by fluoroscopy is either absorbed by the patient or reaches the image detector, ∼0.1% of emitted x-rays “scatter” to be absorbed by the urologist or nearby staff. Occupational standards recommend doses of no more than 5 rem (50 mSV, or ∼75 KUBs) to the entire body and 50 rem (500 mSV, ∼50 CTs) to a single organ annually.¹ Numerous nonmalignant (cataracts, arthropathy) and malignant (lymphoma, leukemia, etc) conditions have been linked to ionizing radiation.² Endourologists must therefore understand the potential harm of occupational radiation exposure and implement strategies to mitigate or eliminate it during these procedures.

ALARA

ALARA (As Low As Reasonably Achievable) principles are designed to limit radiation exposure to patients and medical staff. They are divided into 3 categories: minimizing fluoroscopy time, maximizing distance away from the radiation source, and shielding. Of all these, minimizing fluoroscopy time is reported as the most effective means of reducing radiation exposure.² Strategies to mitigate ionizing radiation are summarized in the Table.

Fluoroscopy Unit Components and Settings

Fluoroscopy units emit x-ray beams from the x-ray tube (Figure 1). By ensuring the tube is underneath the patient, urologists can minimize radiation exposure to their head and upper torso. The image intensifier (or detector) captures x-ray beams and converts them into an image to be displayed on the monitor. Positioning the image intensifier as close as possible to the patient will improve the quality of the image and reduce the necessary radiation dose (Figure 2). The collimator uses apertures (varying size holes) to determine the shape and size of the x-ray beam. By partially closing the aperture, collimation reduces the total x-ray dose that leaves the tube and thus, decreases both patient and scattered dose.

Fluoroscopic images can be produced and captured via 2 different modes. Continuous imaging captures ∼30 frames per second (fps), while pulsed imaging captures 1-15 fps, thereby decreasing effective fluoroscopy time and absorbed dose. In a prospective study of endourology patients, a change in unit default settings from continuous to pulsed imaging reduced entrance skin dose by over 30%.³ Two other elements that have been shown to reduce effective fluoroscopy time are use of a laser aiming beam attachment on the intensifier and last image hold, a feature in which the previous fluoroscopic image continues to be displayed on the monitor.²

Figure 1. Fluoroscopy unit components. The x-ray tube emits x-rays. The image intensifier captures x-ray beams and converts them into an image. The collimator uses apertures to determine the shape and size of the x-ray beam.

Urologist Factors

To best manage spot fluoroscopy times, the urologist should always employ a user-controlled foot pedal. Furthermore, by simply tracking fluoroscopy time and incorporating this into the operative note, urologists may decrease radiation utilization.⁴ While they do not serve a protective role, dosimeters, both badge and ring types, ensure that cumulative radiation exposure is monitored over time.

Distance from the radiation source is another important consideration in radiation safety and should be maximized when possible. According to the Inverse Square Law, which states that radiation intensity is inversely proportional to the square of the distance from the source (I = 1/d²),² fluoroscopic radiation exposure decreases by 75% for every doubling of distance from the source. At most relevant fluoroscopy doses, radiation exposure is therefore expected to revert to background noise at a distance of approximately 3 meters from the x-ray source.

Shielding is the last line of defense for the operating room staff within the radiation field. Examples of different protective shields include lead-impregnated eyeglasses, thyroid shields, chest and pelvic aprons, and gloves. Although the tradeoff of a thicker lead apron is a heavier weight, the amount of radiation attenuated by aprons is estimated to be 90% for 0.25 mm thickness, 95% for 0.35 mm, and 99% for 0.5 mm.⁵ It is critical to handle and store aprons appropriately so that the lead does not crack, and aprons should be tested regularly to ensure proper shielding.

Figure 2. A, The image intensifier is positioned well above the patient, and the x-ray tube is close to the patient. This will result in a higher absorbed dose and a lower quality image. B, The image intensifier is positioned closer to the patient, and the x-ray tube is well below the patient. This will result in a lower absorbed dose and a higher quality image.

Fluoroscopy Alternative Strategies

A variety of techniques have been described to reduce or eliminate fluoroscopy from procedures that have traditionally relied on it. Hsi and Harper described a zero-dose fluoroscopy technique for ureteroscopy utilizing tactile feedback and visual cues for ureteral access.⁶ Although incurring more cost, endoscopic guided percutaneous nephrolithotomy (PCNL) access may reduce fluoroscopy time when compared to conventional PCNL access. Surgeon-directed renal ultrasound is a well-established radiation-free imaging modality for guiding percutaneous renal access during PCNL as well as ureteroscopy and stent placement. MRI, while unlikely to replace fluoroscopy for most image-guided procedures, holds some promise in cystourethrography and is replacing fluoroscopic-guided procedures outside the field of urology (ie, conventional angiograms, defecography).

Adherence to Radiation Safety

Despite the known risks of radiation exposure, ALARA principles are not always followed by urologists. In a survey of Endourology Society members, while 97% of respondents wore lead aprons, only 68% wore thyroid shields, 34.3% wore dosimeters, and 17.3% wore lead-impregnated glasses.⁷ Surveys have suggested that American Urology trainees are not adequately trained in radiation exposure safety.⁸ Recently, a radiation safety training program implemented in a urology residency program was shown to reduce fluoroscopy time by 56%.⁹ Virtual reality simulation training for urology trainees was also shown to reduce fluoroscopy time in PCNL.¹⁰

Conclusion

As the leaders in the operating room or clinic, urologists must understand the potential hazardous effects of ionizing radiation and work to mitigate these risks for their staff. ALARA principles may be adhered to by optimizing fluoroscopy unit settings, limiting fluoroscopy time, shielding, and implementing procedure-specific fluoroscopy alternatives.