Intra-individual Comparison of Average Glandular Dose of Two Digital Mammography Units using Different Anode/Filter Combinations

Rationale and Objectives

The aim of this study was to compare average glandular dose (AGD) in two full-field digital mammography units using different anode/filter combinations.

Materials and Methods

Mammographies of 50 consecutive patients on a mammography system using a tungsten/rhodium (W/Rh) anode/filter combination were retrospectively compared to prior examinations on a different mammography unit using combinations of Molybdenum (Mo) and Rhodium (Rh). To exclude effects of increasing patient age, two prior examinations within 5 years were used. Both views of one breast were chosen for analysis. AGD was recorded as stated by each mammography unit. Accuracy of stated AGD and contrast-detail resolution were assessed using different breast phantoms.

Results

The mean AGDs from the examinations using W/Rh were 0.95 mGy and 1.01 mGy for craniocaudal (CC) and mediolateral oblique (MLO) views compared to 1.51 mGy and 1.54 mGy, respectively, using combinations of Mo and Rh (P < .001). Relative reduction of AGD was independent of breast thickness but decreased with increasing breast density (partial correlation coefficient of 0.46, P < .005 and 0.57, P < .001, for CC and MLO views, respectively). Low-level contrast resolution was equal in both units using standard acquisition parameters.

Conclusion

In clinical mammographies, higher energy beam spectra obtained using W/Rh anode/filter combinations may significantly contribute to lowering AGD compared to Mo/Mo, Mo/Rh, and Rh/Rh in breasts that are not extremely dense.

Key Words: Breast, mammography, radiation dosage, radiation quality, tungsten, rhodium