Uptake quantification of sentinel lymph nodes in breast cancer using SPECT/CT

Objectives Evaluate the feasibility of SPECT/CT for uptake quantification of axillary sentinel lymph nodes (SLN) in breast cancer and analyze the distribution of SLN uptake to define limits of detectability.

Methods Pts with histologically proven T1 breast cancer scheduled for surgery underwent a 2-day protocol was used for the SLN procedure (48-79MBq, Tc-99m nanocol). Static images were acquired on a 2-head camera with LEHR collimators. SPECT/CT was performed immediately after using a hybrid system without reinjection. After attenuation and scatter correction, uptake of the SLN was quantified by defining regions of interest for the injection site and the SLN on the summed coronal images. Overlaying SLNs that could not be simply separated were considered as one. The uptake was defined as percentage of the detected activity in the complete image. Time between injection and visual detection, injected activity and patient information were also documented.

Results In 37 pts (age 29-88) studied, 57 SLNs were detected (0-5 SLNs, median: 1). Time of first visualization ranged 1-25 min p. i. (median: 5 min). In 2 pts SLN uptake was not evaluable as none was visible. In the remaining 35 pts mean SLN uptake was 1.72% (0.01-20.18%, median: 0.53%, SD: 3.02%). In 21 pts the highest SLN uptake was <1%, and in 25 pts <2%. However, we observed an uptake of >2% in 10 pts. Histogram analysis revealed peaks at the lower and upper end of the uptake range. A slight correlation between uptake and amount of SLNs was found (29,8% correlation). The time for detection was <5min for over 65% of pts, being 85% <10min.

Conclusions In this initial work we succeeded to demonstrate that SPECT/CT allows the successful detection of SLN even if the local uptake is considerably <1%.