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Matching Primary and Scattered X-Ray Spectra for Use in Calculating the Diagnostic Radiation Index of Protection

A Pasciak

A Pasciak1*, A Jones2 , L Wagner3 , (1) University of Tennessee Medical Center, Knoxville, TN, (2) MD Anderson Cancer Center, Houston, TX, (3) UT Medical School, Houston, TX


SU-E-I-76 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: Lightweight lead-free or lead-composite protective garments exploit k-edge interactions to attenuate scattered X-rays. Manufacturers specify the protective value of garments in terms of lead equivalence at a single kVp. This is inadequate, as the protection provided by such garments varies with radiation quality in different use conditions. We present a method for matching scattered X-ray spectra to primary X-ray spectra. The resulting primary spectra can be used to measure penetration through protective garments, and such measurements can be weighted and summed to determine a Diagnostic Radiation Index for Protection (DRIP).
Methods: Scattered X-ray spectra from fluoroscopic procedures were modeled using Monte Carlo techniques in MCNP-X 2.7. Data on imaging geometry, operator position, patient size, and primary beam spectra were gathered from clinical fluoroscopy procedures. These data were used to generate scattered X-ray spectra resulting from procedural conditions. Technical factors, including kV and added filtration, that yielded primary X-ray spectra that optimally matched the generated scattered X-ray spectra were identified through numerical optimization using a sequential quadratic programming (SQP) algorithm.
Results: The primary spectra generated with shape functions matched the relative flux in each bin of the scattered spectra within 5%, and half and quarter-value layers matched within 0.1%. The DRIP for protective garments can be determined by measuring the penetration through protective garments using the matched primary spectra, then calculating a weighted average according to the expected clinical use of the garment. The matched primary spectra are specified in terms of first and second half-value layers in aluminum and acrylic.
Conclusion: Lead equivalence is inadequate for completely specifying the protective value of garments. Measuring penetration through a garment using full scatter conditions is very difficult. The primary spectra determined in this work allow for practical primary penetration measurements to be made with equipment readily available to clinical medical physicists.

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