Study compares indirect and direct measurements for both patients and operators
March 28, 2011 Contact: Sue Crosson-Knutson 312-334-2311 firstname.lastname@example.org
CHICAGO - New research published in the April 2011 issue of the Journal of Vascular Surgery®, the official publication of the Society for Vascular Surgery®, directly measured the radiation doses for patients and operators during complex endovascular procedures. Endovascular thoracoabdominal aneurysm (eTAAA) repair was performed in 54 consecutive patients during a five month period; 47 of which had the repair limited to the thoracoabdominal segment. Clinical follow-up was complete in 98 percent of the patients.
“Our study measured direct doses which were then correlated with indirect radiation dose estimates provided by the imaging equipment manufacturers that are typically used for documentation and analysis of radiation-induced risk,” said co-author Roy K. Greenberg, MD, from the department of vascular surgery at the Cleveland Clinic Foundation in Cleveland, Ohio. “Parameters including cumulative air kerma (CAK), kerma area product (KAP) and fluoroscopy time (FT) were recorded concurrently with direct measurements of peak skin dose (PSD) and radiation exposure patterns using radiochromatic film placed in the back of the patient during the procedure.”
No patients developed evidence of radiation-induced skin injury. According to researchers, PSD was only weakly correlated with FT, therefore, FT should not be used to estimate PSD. Even when directly measured PSDs were used, there was a poor correlation with a clinical event (no skin injuries despite an average PSD more than 2 Gy).
Researchers did note that measurements for PSD correlated better with CAK and KAP (r=0.55, 0.80, and 0.76 respectively) but still may represent poor surrogate markers based on The Joint Commission on Accreditation of Healthcare Organizations (JCAHO)-defined sentinel events. The indirect measurement for CAK exceeded 15 Gy (JCAHO’s threshold for sentinel events) in three patients, but when compared with the direct measurements obtained during the procedure, all of the exposures were well below 15 Gy in all patients.
According to Dr. Greenberg, the following formula provides the best estimate of actual PSD = 0.677 = 0.257 CAK. Effective dose was measured by subjecting phantoms, with over 200 dosimeters lodged within mock organs, to similar patterns as observed during the procedures. The average effective calculated dose was 119.68 mSv (for type II or III eTAAA) and 76.46 mSv (type IV eTAAA). Operator exposure was determined using high-sensitivity electronic dosimeters. The operator effective dose averaged 0.17 mSv/case and correlated best with the KAP (r =0.82, P <.0001).
Dr. Greenberg noted that the effective radiation dose of an eTAAA is equivalent to two preoperative computed tomography scans. The maximal operator exposure is 50 mSv/year, thus, a single operator could perform up to 294 eTAAA procedures annually before reaching the recommended maximum operator dose.
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