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Technique Evaluation of Dose Area Product Measurements for Dual-Energy X-Ray Absorptiometer System

J Jimenez*, A Thomas, W Erwin, UT MD Anderson Cancer Center, Houston, TX

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: The aim of this study was to measure the Dose Area Product (DAP) of a Dual-Energy X-ray Absorptiometer (DXA) system to assess the differences between system-reported and external test measurements as part of the Quality Assurance (QA) program.

Methods: A Hologic® Horizon DXA system was used for this study. Dose measurements were performed using a Radcal® Accu-Gold+ multisensor, Radcal® software and a 180cc ion chamber. Field-of-view coverage to assess collimation accuracy was achieved with a computed radiography (CR) plate. Five scan lengths of 4, 5, 6, 7 and 8 inches, and four scan modes of Array, Fast, Express, and High Definition (HD) were measured and analyzed. Array mode is used clinically most often at our institution, but the other modes offer different scan speeds and resolution. The Horizon system achieves this in some cases by adjusting the x-ray beam collimation. Each scan mode therefore provides a balance between scan speed, resolution, and dose.

Results: The CR plate measurements showed that field coverage was within 2.3% of manufacturer specifications. Array mode DAP measurements ranged from 2.01 to 4.10 cGy·cm² with increasing scan length, matching with system reported values within 2.7% on average. Average differences were 3.7%, 9.5% and 32.7% for Fast, Express and HD modes, respectively. Despite the noted large difference between measured and reported DAP values for HD mode, our measurements indicate that Array and HD modes have similar DAP. The manufacturer’s published dose tables for specific scan types and modes indicate the same: Array and High Definition mode produce the same scan dose.

Conclusion: This study shows that a simple setup (180cc ion chamber, CR plate) can reliably measure DAP for a DXA system despite the geometric mismatch between field and chamber. Further testing with other scanners and measurement setups is currently in progress.

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Keywords

X Rays, DEXA, Quality Assurance

Taxonomy

IM- X-Ray: Densitometry (DXA)

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