A preclinical study of prostate sentinel lymph node mapping with [99mTC]diethylenetetramine pentaacetic acid-mannosyl-dextran

Purpose: SLN identification could improve the pathological staging of prostate cancer. Prior SLN studies have been compromised by delayed radiotracer uptake rates and significant diffusion rates out of the sentinel nodes. Lymphoseek (TM) is a new radiopharmaceutical specifically designed for SLN mapping. It shows rapid and sustained SLN uptake. Materials and Methods: We investigated the use of Lymphoseek (TM) for prostate SLN mapping by measuring SLN uptake in 12 anesthetized pigs. The prostate was injected with 0.05 ml of a 1:1 volume per volume mixture of Lymphazurin (TM) and 1.0 mCi Lymphoseek (TM) (1 nmole). Within 5 to 19 minutes the pelvic lymph nodes were dissected and assayed with a gamma probe. A lymph node was considered a sentinel node if it had count rates that exceeded 10 times the background count. We calculated the percent of injected dose of each lymph node excised and the prostate gland. Results: A total of 35 SLNs were identified in the 12 studies. Of the SLNs 81% were located outside of the obturator fossa in this pig model. The SLN percent of injected dose was 0.05% to 7.75% (mean +/- 1 SD 1.74% +/- 1.92%). The mean percent of injected dose in the prostate was 27% +/- 12%. There was no correlation between the side of SLN and the lobe injected. Conclusions: After prostate administration of Lymphoseek (TM) pelvic SLNs attain high signal-to-background ratios within 10 minutes. This property should permit intraoperative injection and SLN mapping without significantly adding to the duration of prostatectomy. A phase I clinical trial has been initiated, which will later incorporate minimally invasive techniques.