Obesity Epidemic Hits Cath Lab, Raising Docs' Radiation Risk

Patrice Wendling

January 10, 2019

The growing prevalence of obesity among Americans may be adversely affecting the health of physicians by exposing them to greater amounts of radiation during coronary angiography, new research suggests.

In a single-center study, physician radiation exposure increased significantly as patient body mass index (BMI) rose, with exposure 7-fold higher when physicians treated the largest (BMI ≥40 kg/m2) vs the leanest (BMI <25 kg/m2) patients (1.4 μSv vs 0.2 μSv; P < .001).

"I don't think most operators consider the impact their patients' BMI might be having on their own radiation doses during procedures, but the impact seems to be intuitive," lead author Ryan Madder, MD, Spectrum Health, Grand Rapids, Michigan, said. "Greater radiation doses are needed to penetrate the additional tissue in obese patients; greater doses result in more scatter radiation."

The study was published online January 2 in Circulation: Cardiovascular Interventions.

Prior studies have linked obesity with radiation dose in patients, but few have examined its effect on radiation exposure in interventional cardiologists, whose main source of exposure is radiation deflected from the patient's body.

Further, the recent uptick in more lengthy and complex catheter laboratory procedures means cardiologists are spending more time in the lab, increasing their lifetime radiation exposure and further increasing the already elevated risks for cataracts, reproductive health problems, and cancer, particularly left-sided brain tumors.

"Obesity is increasingly problematic in our society in general and in our patient population in particular," interventional cardiologist Lloyd W. Klein, MD, Advocate Illinois Masonic Medical Center, Rush Medical College, Chicago, told theheart.org | Medscape Cardiology via email. "This study documents that there are health care implications for the providers of radiologic procedures in that there is more scatter and hence more occupational exposure."

For the study, investigators examined real-time radiation data, including fluoroscopy time, air kerma, and dose area product (DAP), for 1119 consecutive coronary angiography cases in the prospective SHIELD study. Physicians wore a dosimeter on the left anterior side of either their eyeglasses or thyroid collar.

According to standard operating procedure, two lead shields were placed between the operator and patient — a ceiling-mounted upper body shield, and a lower body shield that was attached to the side of the operating table and that extended from table to floor.

The use of radiation-absorbing disposable pads was left to the discretion of the operator and staff; they were used in 59% of cases. The median radiation dose per case for physicians was 0.6 μSv (range, 0.1 - 5.2 μSv).

Obesity was present in 50.1% of patients; 9.6% were morbidly obese. The average BMI was 30.8 kg/m2, and the average age was 66 years.

Compared with a patient BMI of <25 kg/m2, a BMI of ≥40 kg/m2 doubled patient DAP (91.8 Gy·cm2 vs 44.5 Gy·cm2) and air kerma (1097 mGy vs 571 mGy; P < .001 for both). The impact on fluoroscopy time was not statistically significant (7.0 min vs 5.9 min; P = .26).

When the analysis was stratified by procedure, patient radiation dose was again roughly doubled for patients with a BMI of ≥40 kg/m2 for a diagnostic coronary angiography procedure (81.4 Gy·cm2 vs 36.2 Gy·cm2) and percutaneous coronary intervention (PCI) (184.7 Gy·cm2 vs 70.0 Gy·cm2; P < .001 for both).

In contrast, a BMI of ≥40 kg/m2 was linked to a 5.0-fold increase in physician radiation dose per diagnostic coronary angiography (1.0 μSv vs 0.2 μSv; P = .008) and a 23.5-fold increase per PCI (4.7 μSv vs 0.2 μSv; P = .01).

The relatively larger impact of BMI on physician vs patient radiation exposure was "a bit surprising," said Madder, but should be interpreted with caution, given the small number of patients in the highest BMI category.

In multiple regression analysis, each 1-unit increase in BMI was associated with a 5.2% increase in physician radiation dose (95% confidence interval [CI], 3.0 - 7.5).

Performance of fractional flow reserve and PCI was associated with a more than 100% increase in physician radiation dose, although the respective confidence intervals were exceedingly wide (Δ 103.7%; 95% CI, 32.0 - 214.2; Δ 166.7%; 95% CI, 98.0 - 259.3).

Use of a radiation-absorbing pad, which increased significantly across rising BMI categories, was tied to a 69.4% reduction in physician radiation dose (95% CI, 59.4 - 76.9).

"Considering that patient obesity continues to increase, interventionalists should consider adopting more aggressive radiation safety practices to offset the increased occupational radiation exposure that may be occurring in the ongoing obesity epidemic," Madder said.

Novel fluoroscopy systems, including those that utilize real-time image noise reduction technology, have been shown to reduce radiation doses by about 50% or more, but further study is needed to determine their impact for obese patients, the authors note.

The study had several limitations, including a lack of information on body fat distribution and the failure to account for tube angulation, both of which can influence patient and operator radiation dose, the authors note. Variation in dosimeter placement and use of radiation-absorbing pads also may have affected the results or introduced bias. Finally, the use of DAP to estimate patient dose rather than calculating effective doses may be a limitation, although this likely would have resulted in smaller estimations of patient radiation doses, they suggest.

The study is "very well done," Klein said. "The main limitation is that these increments may or may not have a clear health impact on workers. But it sends a strong message that such an impact is likely."

Going forward, the question is how to protect against this risk.

"We can't stop cathing obese patients, but we can be sure that we are as protected as possible," he said. "The solutions might include robotics, self-enclosed suits, shielding from toe to head, and there are commercial products available that do provide all of these advantages. But physicians need to be sure that they are available in their labs and that they are being used correctly."

The study was partially funded by a research grant from Corindus Vascular Robotics. Dr Madder has received significant research grants and has served on the advisory board of Corindus. The other authors and Dr Klein have disclosed no relevant financial relationships.

Circ Cardiovasc Interv. Published online January 2, 2019. Abstract

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