Radiation doses calculated in thoracoabdominal aneurysm repair cases

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New research directly measured the radiation doses for patients and operators during complex endovascular procedures. The study was published in the April 2011 issue of the Journal of Vascular Surgery.

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 completed in 98% 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 research’s co-author Roy K Greenberg, Department of Vascular Surgery, Cleveland Clinic Foundation, Cleveland, Ohio, USA.

“Parameters including cumulative air kerma, kerma area product and fluoroscopy time were recorded concurrently with direct measurements of peak skin dose 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, peak skin dose was only weakly correlated with fluoroscopy time, therefore, this should not be used to estimate peak skin dose. Even when directly measured peak skin doses were used, there was a poor correlation with a clinical event (no skin injuries despite an average peak skin dose more than 2 Gy).

Researchers did note that measurements for peak skin dose correlated better with cumulative air kerma and kerma area product (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 cumulative air kerma 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 Greenberg, the following formula provides the best estimate of actual peak skin dose = 0.677 = 0.257 cumulative air kerma. 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 kerma area product (r =0.82, P <.0001).

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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