The quality assurance of digital mammogram has been included in the Standards of Medical Exposure Quality Assurance in Taiwan since July, 2008. According to the Standards, determination of the half-value layer (HVL) is an integral part of mammographic dosimetry which requires the evaluation of patient's glandular dose. The purpose of this study was to develop a simple method to help hospitals determine the HVL. A compact device, accommodating Harshaw TLD-100H (LiF:Mg,Cu,P) chips and aluminum sheets in a small holder, was designed to determine the HVL under clinical exposure conditions (tube voltage, target/filter) of a digital mammographic unit. This device was used to determine the HVL ranging from 0.3- to 0.5-mm Al. Air KERMA measured by the TLDs were corrected for scatter radiation and energy dependence caused by the aluminum sheets. Once scatter and energy dependence were corrected, the agreement of determined HVLs was within ±7% with measured data using the ionization chamber. This device provides a simple, inexpensive and remote means to reliably audit the HVL of a mammography unit on a periodic basis.
- Half-value layer (HVL)
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