Local Diagnostic Reference Levels in Digital Breast Tomosynthesis

Diagnostic Reference Levels (DRLs) are a guideline to indicate whether the radiation administered during medical procedures performed under routine conditions is unusually low or high. Currently, there are no national DRLs in Australia for Digital Breast Tomosynthesis Mammography (DBT). Given the radiosensitivity of breast tissue, establishing DRLs for DBT is of great importance. This research aims to develop Local Diagnostic Reference Levels (LDRLs) for DBT that can be used as a guide for monitoring radiation delivery levels, and a Quality Assurance tool to assist in monitoring the performance of the mammography unit.

Average Glandular Dose (AGD) was collected from patient data through OpenREM software. Other data collected included breast density, compression force, compressed breast thickness (CBT), operative and treatment status. LDRLs were set using the 75th percentile (third quartile AGD values), categorised into four CBT ranges and compared against the median AGD values.

LDRLs were similar for both craniocaudal and mediolateral oblique views. LDRLs for CBT ranges of 13-49 mm, 50-74 mm, 75-99 mm and 100-118 mm were calculated to be 1.5, 2.70, 3.90 and 4.70 mGy, respectively. There was no statistically significant correlation between breast density and AGD.

It was found that CBT had a larger impact on dose than density. Significant differences were found between the LDRLs for each of the CBTs; therefore, setting a single LDRL for all CBTs may result in missing unacceptably high or low breast doses. LDRLs should be reviewed frequently to ensure the radiation dose patients receive is within optimal levels.