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Estimating Peak Skin Dose in the Cath Lab Using Gafchromic Film

A Scott

A Scott*, Y Zhou , J Nute , C Lee , J Allahverdian , Cedars-Sinai Medical Center, Los Angeles, CA


PO-BPC-Exhibit Hall-23 (Saturday, March 5, 2016)  Room: Exhibit Hall

Purpose:The FDA requires fluoroscopy units manufactured after 2006 to provide the displayed air kerma (DAK) measured at the Interventional Reference Point (IRP), which is 15 cm from the isocenter towards the tube. However, from a radiation safety perspective, the quantity of interest is the peak skin dose (PSD) as erythema may occur at a PSD threshold of 2 Gy. We used Gafchromic film to investigate a correlation between DAK and PSD in the catheterization lab.

Methods:In order to relate dose to Gafchromic film optical density (OD), a batch of Gafchromic film was calibrated by exposing pieces to a range of AK levels (0.25 Gy to 10.0 Gy) using DSA mode in a GE cath lab while measuring the AK using a Radcal ion chamber. The film OD was measured by scanning the film with an Epson 10000XL, splitting the image into RGB channels, and measuring the red-channel pixel values using ImageJ. A saturation-growth model was fit to the distribution of pixel values vs. AK to provide an OD-to-dose calibration. To measure PSD, a sheet of film was placed on the patient table during a cardiac procedure and collected along with the accumulated DAK. Afterwards, the peak OD of the film was measured and the PSD was calculated using the calibration.

Results:The PSD and uncertainties for 12 procedures were compared to accompanying DAK records and the ratio calculated. The average PSD calculation uncertainty was 6%. With the exception of one outlier, the average ratio of measured-to-displayed air kerma was 0.36±0.08 with a range of 0.28 to 0.49.

Conclusion:We found a correlation between DAK and PSD in the procedures studied and can make an improved estimate of PSD compared to using beam time. This will improve the accuracy of radiation dose warnings for high-dose cath lab procedures.

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