Clinical feasibility of a high sensitivity intra-operative hand-held gamma camera (IHGC) for sentinel lymph node biopsy (SLNB)

Objectives IHGC imaging can lower false negative rate in SLNB by resolving ambiguities during the use of a non-imaging counting probe (CP). We performed a study to determine if an IHGC: 1) was more sensitive and specific than a CP alone; and 2) could form images of SLNs in 20sec or less.

Methods A high sensitivity IHGC with a 5 x 5 cm^2 field of view (FOV) was used in conjunction with a hand-held CP. 30 melanoma and 8 breast cancer patients underwent a SLNB protocol with 1) preop lyphoscintigraphy (PLS); 2) localize and record counts from SLN in the OR with CP; 3) image SLN with IHGC in the OR for only 1-20sec; 4) surgically remove that SLN; 5) record counts from SLN ex-vivo with CP; 6) image SLN ex-vivo with IHGC; 7) repeat step 2, until no SLN are found with CP; 8) scan with IHGC to find occult nodes; 9) attempt to re-localized any occult SLN with CP; 10) Compare OR findings of SLN with path results. A true positive (TP) for the CP was defined as > 100 cps in-vivo and ex-vivo. A false negative (FN) for the CP was no-detection in-vivo with CP, but detection of > 5 cps by both IHGC in-vivo and CP ex-vivo. TP for the IHGC was > 5 cps for both IHGC in-vivo and CP ex-vivo. FN for the IHGC was non-detection for the IHGC in-vivo and > 100 cps CP ex-vivo.

Results PLS localized 67 radioactive SLN (of which 8 were internal mamary nodes). 70 TP and 8 FN resulted using the CP versus 73 TP and 5 FN for the IHGC. OR time was not increased. 14 pathology positive SLN were detected by IHGC(14) and CP(13).

Conclusions At this point, IHGC is promising but the FN rate was not significantly different than for the CP (p<0.2, for t-test with 38 patients).

Research Support This work was supported in part by the Whitaker Foundation under Grant No. RG-01-0492