Primer on radiation exposure and protective equipment

Clinical practice

Interventional radiology is an essential part of contemporary patient care. IR owes its minimally invasive nature to the powerful capabilities of imaging technology, often based on x-ray radiation in the form of fluoroscopy. It is critical, then, for IRs-in-training to understand the potential effects of radiation exposure, including long-term health risks encountered in the field and the importance and methods of appropriate radiation protection.

Radiation exposure in IR

Although the risk of radiation-exposure-related injury as a result of fluoroscopy-guided procedures is low, one should pay attention to radiation exposure, as it is cumulative. Radiation dose varies with several factors, most notably the nature and complexity of the procedure. A prospective study examining IR procedures showed that transjugular intrahepatic portosystemic shunt (TIPS) carried the highest dose area product (DAP), followed by vascular embolization and hepatic transarterial chemoembolization.1 Radiation dose also varies with spatial and temporal resolution as well as the patient’s body habitus.2 A Japanese retrospective study that analyzed occupational radiation exposure to different members of the IR team showed that physicians encountered the highest dose, followed by nurses and radiology technologists.3

Radiation effects are broadly categorized as deterministic or stochastic. In deterministic effects, there is a cause-and-effect relationship between radiation exposure dose and its consequences. Deterministic effects have a threshold radiation exposure, below which the effect will not occur, and above which the severity of the effect increases with dose. An example of a deterministic effect is radiation-induced cataracts. The ocular lens is highly radiosensitive, with an approximate 0.5 Gy threshold for cataract induction, lower than previously thought.4

On the other hand, stochastic effects, such as radiation-induced cancer, occur without a threshold point and increase in probability proportionately with dose. Tissues are ascribed weighting factors in calculating equivalent radiation dose, based on their demonstrated radiation exposure-related carcinogenic risk.5 High-risk tissues include stomach, colon, lung and red bone marrow. Breast, liver and thyroid are among moderate-risk tissues, while cortical bone and skin are low-risk tissues.

Dosimeters and protective equipment

Dose monitors are vital in the routine assessment of one’s radiation exposure. Conventional badge monitors are worn at the waist (under the lead apron) and at the neck (over the lead thyroid collar) to estimate the absorbed dose for abdominal organs and the thyroid gland, respectively. The most recent recommendations of the International Commission on Radiological Protection (ICRP) include an annual dose limit for whole-body exposure set at 20 mSv per year averaged over 5 years, with no year exceeding 50 mSv—which is 7.5 times lower than the current limit set by the Nuclear Regulatory Commission.6 Hand exposure is of concern for IR physicians since tool manipulation often occurs close to the x-ray field. For this reason, several institutions have adopted the use of ring dosimeters, which are worn on the pinky or ring finger of the hand nearest to the x-ray tube.7

While the lead vest, apron and thyroid shield are invaluable components of radiation protection for the IR physician, the cumulative stress of bearing this added weight is associated with various orthopedic injuries. Protective aprons are assigned “lead-equivalence” values, which represent their ability to attenuate x-ray beams of different energies. Recent studies on a novel lead-free lightweight material composed of barium sulfate and bismuth oxide have shown protection similar to standard 0.5-mm lead-equivalent protective gear with greater comfort at only half the weight.8,9 Trainees should be aware of this option as they obtain their equipment. However, they also need to know that conferred degrees of radiation protection from protective gear vary based on the energy of the utilized x-ray beam and may be different in modalities other than traditional fluoroscopy, such as cone-beam CT.

Lead goggles should also be worn in the operating suite. Typically, they have a higher lead equivalency than aprons, usually around 0.75-mm of lead equivalence. In selecting goggles, trainees should consider effective side shielding and proper fit to minimize radiation dose to the eye.10

Considering most of radiation exposure during IR procedures is scatter radiation, IRs-in-training should exercise reducing scatter by using above and below table shielding, applying optimized adaptive collimation, using low-framerate pulsed fluoroscopy, and reducing the distance between the image intensifier and the patient.

In IR, you must always remember to take care of yourself to care for your patients. Though radiation metrics and their translation to health effects may seem elusive at first, IRs-in-training must practice choosing the appropriate gear, be familiar with procedural factors that contribute to radiation dose, and be aware of potential health effects of radiation exposure during IR procedures.

References

  1. Bundy JJ, Chick JFB, Hage AN, et al. Contemporary interventional radiology dosimetry: Analysis of 4,784 discrete procedures at a single institution. J Am Coll Radiol. 2018;15(9):1214–1221.
  2. ACR Image Wisely. imagewisely.org/Imaging-Modalities/Fluoroscopy/Patient-Specific-Factors.
  3. Chida K, Kaga Y, Haga Y, et al. Occupational dose in interventional radiology procedures. AJR Am J Roentgenol. 2013;200(1):138–41.
  4. Bolch WE, Dietze G, Petoussi-henss N, Zankl M. Dosimetric models of the eye and lens of the eye and their use in assessing dose coefficients for ocular exposures. Ann ICRP. 2015;44(1 Suppl):91–111.
  5. The 2007 recommendations of the international commission on radiological protection. ICRP publication 103. Ann ICRP. 2007;37(2–4):1–332.
  6. Frey GD. Radiation cataracts: New data and new recommendations. AJR Am J Roentgenol. 2014;203(4):W345–6.
  7. Martin CJ. Personal dosimetry for interventional operators: When and how should monitoring be done? Br J Radiol. 2011;84(1003):639–48.
  8. Uthoff H, Peña C, West J, Contreras F, Benenati JF, Katzen BT. Evaluation of novel disposable, light-weight radiation protection devices in an interventional radiology setting: A randomized controlled trial. AJR Am J Roentgenol. 2013;200(4):915–20.
  9. Uthoff H, Benenati MJ, Katzen BT, et al. Lightweight bilayer barium sulfate-bismuth oxide composite thyroid collars for superior radiation protection in fluoroscopy-guided interventions: A prospective randomized controlled trial. Radiology. 2014;270(2):601–6.
  10. Sturchio GM, Newcomb RD, Molella R, Varkey P, Hagen PT, Schueler BA. Protective eyewear selection for interventional fluoroscopy. Health Phys. 2013;104(2 Suppl 1):S11–6.