Study Calculates Radiation Doses in TAAA Repair Cases

March 28, 2011—The Society for Vascular Surgery announced the publication of new research that directly measured the radiation doses for patients and operators during complex endovascular procedures. Giuseppe Panuccio, MD, et al published the findings in the Journal of Vascular Surgery (2011;53:885–894).

Co-investigator Roy K. Greenberg, MD, commented, “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. 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.”

According to the Society for Vascular Surgery, endovascular thoracoabdominal aortic aneurysm repair (eTAAA) was performed in 54 consecutive patients during a 5-month period. The repair in 47 of these patients was limited to the thoracoabdominal segment. Clinical follow-up was complete in 98% of the patients. The investigators reported that no patients developed evidence of radiation-induced skin injury.

The investigators found that PSD was only weakly correlated with FT and concluded that 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 > 2 Gy).

According to the investigators, the measurements for PSD correlated better with CAK and KAP (r = 0.55, 0.8, and 0.76, respectively) but still may represent poor surrogate markers based on sentinel events as defined by the Joint Commission on Accreditation of Healthcare Organizations. The indirect measurement for CAK exceeded 15 Gy (the threshold for sentinel events as defined by the Joint Commission on Accreditation of Healthcare Organizations) 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.

Dr. Greenberg stated that the best estimate of actual PSD is provided by the following formula: 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 eTAAAs annually before reaching the recommended maximum operator dose.