A new study, presented at the 64th Vascular Annual Meeting presented by the Society for Vascular Surgery® today, assessed the accuracy of indirect estimated radiation doses of 47 patients during endovascular thoracoabdominal aneurysm repair (eTAAA).
"The standard methods of reporting and documenting peak skin dose is the indirect assessment provided by the imaging system and when used alone there were patients in our that had study with greater than 15Gy in exposure based upon the indirect estimate report provided by the imaging system," said Dr. Roy Greenberg, vascular surgeon in the departments of vascular surgery, radiology, cardiothoracic surgery, and biomechanical engineering at the Cleveland Clinic.
"Fluoroscopy time (FT), cumulative air kerma (CAK) and kerma air product (KAP) represent poor methods used to estimate peak skin dose (PSD) during aortic procedures when compared with directly measured PSD." Furthermore, the study concluded that "these estimates as well as the threshold applied to direct measurements did not correlate with clinical events." The patients undergoing eTAAA had imaging system generated indirect radiation parameters recorded concurrently with direct measurements of radiation exposure patterns using radiochromatic film. Observed radiation exposure patterns were then reproduced in phantoms lined with hundreds of dosimeters located within mock organs, allowing for effective radiation dose calculations. Operator dose was also assessed using electronic dosimeters.
When the researchers compared the direct measurements and indirect reports from the imaging system using scatter plots and Pearson coefficients, there appeared to be a marked discrepancy between the estimated dose (provided in all cases automatically by the machine) and the directly measured dose. In spite of the fact that the CAK exceeded 15Gy in three patients, direct measurements never exceeded 15Gy in any patient. The PSD, quantified using gafchromic film, correlated very weakly with FT, but much better with CAK and KAP, particularly when a conversion formula described in the study was used. No patients in the clinical study developed any evidence of radiation induced skin injury. The mis-match between indirect and direct measurement likely relates to the method by which indirect measurements are calculated, which relates more closely to cardiac procedures rather than peripheral vascular procedures or aortic procedures, according to Dr. Greenberg.
"We found that the formula provides the best estimate of actual PSD," said Dr. Greenberg. "The average effective dose was 119.68mSv (for type II or III eTAAA) and 76.46mSv (type IV eTAAA). Mean operator effective dose was 0.17mSv/case, and correlated best with KAP
"The effective radiation dose of eTAAA is equivalent to two preoperative CT scans," said Dr. Greenberg. "An operator could perform up to 294 eTAAA annually before reaching the maximum recommended operator dose. Thus, the validity of the estimated dose is in question and was typically off by 50 percent or more in our cases. Given that JACHO standards are all based on the estimated dose, and the estimated dose for aortic procedures is very inaccurate, peripheral vascular/aortic procedures are not being assessed properly. We believe these are critical issues with regard to radiation exposure and this will result in problems with hospital documentation and reporting sentinel events."
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