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Increased patient BMI ups physician radiation exposure in cath lab
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Increased BMI among patients undergoing coronary angiography procedures is linked to greater physician radiation exposure, according to data published in Circulation: Cardiovascular Interventions.
For the study, Ryan D. Madder MD, from the Frederik Meijer Heart and Vascular Institute of Spectrum Health in Grand Rapids, Michigan, and colleagues collected real-time radiation exposure data during coronary angiography procedures.
“We were concerned that the increasing prevalence of obesity among patients undergoing catheterization could be impacting the radiation doses received by interventional cardiologists,” Madder wrote in an email to Cardiology Today’s Intervention.
The researchers used dose area product to estimate radiation exposure for the patient and, for physicians, radiation dose was recorded using a dosimeter worn in the cath lab and was reported as personal dose area equivalent.
Results showed that both patient dose area product and physician radiation dose increased across all BMI categories (P < .001) among the 1,119 coronary angiography procedures included in the study. Patient radiation dose was approximately twice as high among patients with morbid obesity vs. lean patients (dose area product, 91.8 Gy x cm2 vs. 44.5 Gy x cm2; P < .001). Similarly, for physicians, radiation exposure was seven times higher during procedures with morbidly obese vs. lean patients (1.4 μSv vs. 0.2 μSv; P < .001).
Patients with BMI less than 25 kg/m2 were considered lean; those with BMI between 25 kg/m2 and 29.9 kg/m2 were considered overweight; those with BMI between 30 kg/m2 and 34.9 kg/m2 were considered to have class I obesity; those with BMI between 35 kg/m2 to 39.9 kg/m2 were considered to have class II obesity; and those with a BMI of 40 kg/m2 or greater were considered to have morbid obesity.
Overall, 17% of the study population was lean, 50.1% was obese and 9.6% was morbidly obese.
Predictors of radiation exposure
When analyzed according to procedure, Madder and colleagues found that physician radiation dose was approximately twice as high during diagnostic angiography vs. PCI procedures. When involving patients with morbid obesity vs. lean patients, physician radiation dose was fivefold higher during diagnostic coronary angiography procedures (1 μSv vs. 0.2 μSv; P = .008) and 23.5-fold higher during PCI (4.7 μSv vs. 0.2 μSv; P = .01).
“This dramatic increase in dose was surprising, but should be interpreted with caution since the number of morbidly obese patients undergoing PCI was relatively small,” Madder said. “Based on this finding, I think there is a need to develop a more thorough understanding of the impact of patient morbid obesity on cath lab radiation safety.”
In multiple regression analysis, there was a significant independent association between patient BMI and physician radiation dose, which increased by 5.2% with every increase in BMI unit (P < .0001). Age, PCI and fractional flow reserve were also independently associated with increased physician radiation dose. However, use of radiation-absorbing pads, which physicians used more often across increasing BMI categories (P = .007), was independently associated with a 69.4% reduction in physician radiation dose (P < .0001).
The researchers noted, however, that this was a single-center, prospective, observational study and its design plus variability in data suggest low precision among the predictors.
There were also several potential limitations. For instance, distribution of body fat was not recorded and there was no accounting for tube angulation, both of which affect radiation dose. Dosimeters were also not worn in the same location by all physicians and the use of radiation-absorbing pads differed across BMI categories, all of which may have influenced results, the researchers wrote.
“Given that our findings were generated in a single-center study, I would like to see if the results can be replicated at other centers,” Madder said.
Effect of the ‘obesity epidemic’
The observation of increasing physician radiation exposure with higher patient BMI is consistent with the notion that higher patient radiation doses, which appear to increase with patient BMI, are linked to higher amounts of scatter radiation — the major source of radiation exposure to physicians in the cath lab, according to Madder and colleagues.
“Considering the increasing recognition of the health risks faced by interventional cardiologists, combined with the growing prevalence of obesity in the catheterization laboratory, the observations of the present study perhaps call for more aggressive radiation safety practices in the era of the obesity epidemic,” they wrote.
Madder and colleagues also noted that the increased use of radiation-absorbing pads during procedures involving patients with higher BMIs suggests that physicians are cognizant of the potential for increased radiation exposure under those circumstances, but more research is necessary to determine how best to reduce radiation exposure in the cath lab.
“The take-home message is that increasing patient BMI is associated with greater physician radiation doses during coronary angiography. I hope that this study helps interventional cardiologists to consider the impact that their patient’s BMI might have on their own radiation dose and drives them to optimize their own radiation safety practices,” Madder told Cardiology Today’s Intervention. – by Melissa Foster
For more information:
Ryan D. Madder, MD, can be reached at ryan.madder@spectrumhealth.org.
Disclosures: This study was partially funded by a research grant from Corindus Vascular Robotics. Madder reports he has received research grants and served on the advisory board of Corindus Vascular Robotics. The other authors report no relevant financial disclosures.
Perspective
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Lloyd W. Klein, MD
Obesity is increasingly problematic in our society in general, and in our patient population in particular. 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.
I am not sure that there is any implication of this study directly for patients. However, it definitely suggests that physicians and nurses/technologists who work in the lab are at risk for increased exposure. The main study finding is that physician radiation dose increased 7.1-fold in a step-wise manner based on patient BMI.
Also, the authors found that "compared with a BMI < 25, a patient BMI ≥ 40 was associated with a 2.1-fold increase in patient radiation dose.” This is a highly substantial increase in exposure.
Scatter is the main cause of radiation to health care personnel, and obesity will cause higher air kerma to be produced in order to penetrate to create diagnostic images. Table 3 in the study demonstrates this. Figure 2 shows that there is a clear correlation between patient BMI and physician radiation dose.
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.
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. The solutions might include robotics, self-enclosed suits and shielding from toe to head. There are also commercial products available that do provide all of these advantages. However, physicians need to be sure that they are available in their labs and that they are being used correctly.
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