Scatter Radiation and Ergonomics in the Cardiac Catheterization Lab
Robert Shealy, PhD
Trans-Radial Solutions
Interventional cardiologists (operators) and their table-side assistants are among the most heavily exposed medical professionals to occupational X-radiation. 1,2 Diagnostic and interventional cardiology procedures require close proximity to scatter radiation emanating from the patient during fluoroscopy and cineangiography ("cine"). Efforts to minimize these exposures include advanced X-Ray equipment design and operational protocols, as well as a variety of shielding devices.
Health effects of long-term, low-level radiation exposure are well documented in the medical literature. Perhaps the most prominent effects on the interventional operator and staff are lens cataract formation and an increased incidence of left-sided brain tumors. 3,4,5 Increased incidences of breast cancer 3,4 and chromosome damage 1 have also been documented. In a 2015 SCAI (Society for Cardiovascular Angiography and Interventions) survey of 314 members, 6.9% of operators had been forced to limit their caseload because of excess radiation exposure. 6
Operator exposures may be highest during emergency PCI procedures involving myocardial infarction (MI), 7 indicating that some precautions are more likely to be compromised in an emergency. Head and eye exposures 1,2,5 are of special significance, both because of their susceptibility to injury and because shielding which protects the head must not interfere with operator vision and mobility. Picano, et al, found that "less protected" parts of the body (e.g. head and hands) can receive doses up to 50 mSv per year. 4 Head and eye protection is thus normally inferior to shielding for the operator's torso and thyroid. Also, in order to preserve mobility and tactile sense, arm and hand shielding is usually weak or absent.
In 2013, new standards adopted by the International Atomic Energy Agency (IAEA) reduced radiation exposure to the eyes from 150 mSv per year to 20 mSv per year, averaged over defined periods of 5 years, with no single year exceeding 50 mSv. 8 The head dose sustained by cardiologists may occasionally exceed even the old eye exposure standard of 150 mSv per year.1 Interventional radiologists and their staff, if not using shielding eyeglasses, may easily exceed the new eye limits. 9 The shielding effect of glasses may provide a 60% reduction in eye exposure, 9 but with little or no protection for the rest of the operator's head. The ever-increasing frequency and complexity of vascular procedures makes the need for additional and improved operator head area protection obvious and imperative.
Operator dose depends upon several important variables. 10 Exposure may vary with choice of access site. The transradial approach has long been associated with increased operator exposure. An American College of Cardiologists (ACC) 2017 presentation 11 found that operator radiation exposure using the transradial approach was nearly twice that of the femoral approach. Since transradial access often involves fluoroscopy of radial loops and other anomalies, as well as subclavian tortuosities, both of which are closer to the operator, an increased operator exposure should be expected. In addition to access site, important variables include patient BMI, operator location 12, and procedure complexity. Operators performing transradial procedures with the patient's arm abducted up to 90 degrees may be closer to the scatter radiation source (heart) than with the patient's arm by his/her side. The extent of cine versus fluoroscopy is of major importance, since cine may be responsible for 5 times the radiation dosage of fluoroscopy. 13 Catheterization table height may also contribute significantly to operator exposure. Haquanni, et al, showed that at table heights above 105 cm, radiation exposure to the operator increases by 0.12 mSv/hr for each cm increase in height. 14
Shielding is essential to minimizing operator radiation exposure. Traditional shielding includes a ceiling-mounted, leaded acrylic shield, an under-table shield, radiation-blocking garments (aprons, thyroid, cranial) and leaded eyeglasses worn by operators and staff. 15 Elemental lead (Pb) sheeting is the standard radiation absorbing medium for protection from medical X-Rays. Lead-free shielding (e.g. using bismuth) promises light weight and safe disposability, but has been shown to be inferior to lead, even at equivalent weights. 16,17,18 Highly effective lead shielding is compatible with the best-protected operator body areas, such as the torso, legs and lower neck, but contributes to important orthopedic issues among operators and other staff. Kumar, et al 3 reported significant levels of orthopedic injury in 49% of operators surveyed.
A variety of published reports evaluate protective devices either by using "phantoms" (blocks of plastic or artificial torsos) or empirically, i.e. in "the real world" setting of the cardiac catheterization laboratory. Studies of the same device may yield results varying from 0% protection to the operator's head to 25% or more. 16,17 Placement of the phantom or patient in relation to the protective device and radiation meter or dosimeter is obviously critical to obtaining usable results.
User-friendliness and adaptability to access site cross-over ("bail out"), and to emergent, as well as non-emergent, procedural settings may be at least as important as scatter radiation protection. Quick and simple set-up is an absolute necessity in an emergency (e.g. STEMI) situation. Any device needing more than 60 seconds to set up may simply be left out. 7 Other critical requirements include non-interference with C-arm operation, organization and support of percutaneous devices (catheters, manifolds, syringes, etc.), ease of physician and assistant access, and the ability to easily cross over to any alternate access site (left radial, femorals, and ulnars).
Exposure of medical professionals to scatter radiation, especially to the eyes and head, is thus a major health concern, and is projected to grow in the face of increasing numbers and complexity of procedures. The challenge is to produce and improve devices and practices which minimize these exposures. It is axiomatic that devices and practices are only as good as practitioner compliance. This compliance depends not only on proven effectiveness, but also on convenience and non-interference in, if not actual facilitation of, the procedure at hand. Verifying real-world dose reduction must go beyond manufacturer claims and will ultimately depend upon proactive practitioner involvement. 18
CITATIONS
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