SPECT-CT Guided Lymphatic Mapping and Sentinel Lymphadenectomy (LM/SL) in Prostate Cancer

A multidisciplinary team (urologist, oncologist, radiologist, pathologist, and nuclear medicine) will assess the technical feasibility of LM/SL with SPECT/CT as well as its clinical potential for the staging of regional lymph nodes in 30 consecutive patients with AJCC stages I-II-III prostate cancer scheduled for prostatectomy and pelvic lymph node dissection according to the standards of care. This is a 2-day protocol with a single isotopic tracer (Tc99m-cysteine rhenium colloids, 10-15 nm). The tracer injections will be performed under trans-rectal ultra-sound guidance (1 inj/lobe, 74MBq, 0.2 cc). The first day or injection day (D0), an early imaging session with planar acquisitions (anterior and posterior views) will be performed within 30 min post-tracer injection. A delayed imaging session with planar and SPECT/CT acquisitions will be also performed 1 to 3 hours after tracer injection. The SPECT/CT device to be used in this research protocol is the Infinia Hawkeye 4-slice from GE Healthcare. This hybrid camera incorporates a low-dose CT with a 2.5 mA current (eff.dose \< 2mSv) on a dual-head gamma camera. SPECT/CT data will be analysed on the Xeleris 2.05v (Volumetrix for Hawkeye Oncology). The second day (D+1 post-tracer injection), all prostate cancer patients will undergo a radical prostatectomy with complete pelvic lymph node dissection (CLND). Sentinel lymph nodes (SLNs) will be detected intra-operatively by using a gamma probe (Navigator, Tyco Healthcare). In this single tracer study, SLNs are defined as hot nodes only including the hottest node and any hot node ≥ 10% of the hottest node. In this SPECT/CT protocol, additional non-radioactive nodes eventually detected on the CT component and suspicious of tumor involvement (lymphadenopathies \> 1cm) will be also removed, especially lymph nodes located in unpredictable lymphatic basins. Surgery will be performed by the same surgeons. SLNs and non-SLNs will be analyzed by the same pathologist. For SLNs, a Hematoxylin \& Eosin staining (H-E) will be firstly performed. If negative, 3 more H-E stains levels will be performed and immuno-peroxidase stains for Cytokeratins AE1/AE3, PSA, and PAP. Non-SLNs will be analyzed according to the routine protocol with 3 H-E stained levels only. The SLN features will be noted: number, anatomical localization in vivo, counting rates ex vivo. The pathological characteristics of metastatic SLNs and non-SLNs will be precisely recorded: size, involvement (micro-metastases ≤ 2mm; macro-metastases; isolated tumor cells), % of nodes involved (small \< 25%; moderate = 25-75%; massive \> 75%).