Quantifying molecular breast imaging uptake variability and changes in patients with breast cancer undergoing neoadjuvant therapy.

RATIONALE AND

OBJECTIVES

Best practices for quantifying longitudinal changes in 99m Tc-sestamibi uptake with molecular breast imaging (MBI) have not been established. The objective of this work is to quantify the variability of tumor-to-normal tissue 99m Tc-sestamibi uptake measurements in patient data and the resulting impact on categorizing uptake changes throughout neoadjuvant systemic therapy (NST).

MATERIALS AND

METHODS

In 60 patients with locoregional breast cancer undergoing NST, tumor-to-normal-tissue ratios of average contour counts ( ) and activity concentrations ( ) were calculated from physician contours on craniocaudal and mediolateral-oblique MBI images acquired at pre-NST, mid-NST, and post-NST with a commercial dual-headed system. Measurement variability was quantified in pre-NST images by using different contours and detector views. This analysis was then used to define patient-specific thresholds above which calculated and values at mid-NST and post-NST imaging had 'changed' from pre-NST values.

RESULTS

Pre-NST values ranged from 1-5 to 1-100 and in general decreased by 10-30% at mid-NST and by 50-70% at post-NST. uncertainty was significantly higher than uncertainty (53% vs. 35% median value; paired t -test; P  < 0.007), driven primarily by normal-tissue contour placement within the heterogeneous signal in normal breast parenchyma. In paired comparisons, a significantly higher number of cases 'changed' when the metric was derived from a single image instead of averaged across images (McNemar's test, P  < 0.0125).

CONCLUSION

By ensuring consistent acquisition conditions and standardizing contour definitions, robust metrics of tumor and normal-tissue uptake can be extracted from heterogenous clinical MBI data for longitudinal quantitative evaluations.