Radioisotopic detection of sentinel lymph nodes in clinically localized high-risk prostate cancer

Purpose: To explore the efficacy of a radioisotopic (RI) method in detecting sentinel lymph nodes (SLNs), known as sites of harboring metastases, in localized high-risk prostate cancer (HRPC). Methods: The RI method was applied to 26 males with clinically localized HRPC, subjected to radical prostatectomy in 2006-2008. All had poor pathological characteristics: initial PSA > 15 ng/ml, Gleason score > 7, clinically suspected extracapsular extension, seminal vesicle invasion, and/or positive pelvic lymph nodes (LNs). The radiopharmaceutical (Tc-99m) was injected preoperatively at 4 zones of the periphery of the prostate. Tc-99m-nanocolloid particles were <= 80 nm in size, with total activity of 3 mCi (111 MBq), diluted in 2 mL. One hour after Tc-99m administration, a planar scintigraphy was performed on a gamma camera in anterior posterior and lateral projections. A high resolution collimator was used, gathering impulses up to 300 000 per frame. The precise location of the SLNs was determined intraoperatively by a gamma probe. The LNs removed by extended pelvic lymphadenectomy were arranged on an anatomical template, examined ex vivo by the gamma probe and scanned again. The LNs were cleaned from the adjacent fatty tissue, fixed in neutral formalin, and then processed separately for histological and immunohistochemical examination. Results: The number of surgically removed LNs ranged from 9 to 38 (mean 13), and the SLAs from 1 to 7 (mean 3). The SLNs were visualized on lymphoscintigraphy as strictly defined, round zones of high activity and were easily recognized intraoperatively by the gamma probe. The scintigraphic images of the scanned anatomical templates correlated well with those prior to surgery. Histology confirmed LN metastases in 11 cases. 94% of the metastatic LNs were SLNs, accurately detected by the RI method. Only 2 metastatic LNs showed no activity prior to, and during the operation. Most of the metastatic LNs (62%) were SLNs, located out of the obturator fossa. Conclusion: The radioisotopic detection of the SLNs in HRPC is an objective and sensitive method that aids the surgeon to take a proper decision regarding the scope of the pelvic LN dissection in each particular case.