Pelvic Side Wall Lymph Node Detection in Rectal Cancer Using Dual Radioisotope and Fluorescence Guidance

Background Total mesorectal excision (TME) revolutionised the management of rectal cancer by improving outcomes and standardising surgical technique. When excising mesorectal lymph nodes, most involved nodes are removed. However, a proportion of lower rectal lymphatic drainage is through the pelvic sidewall (PSW) system, all PSW nodes are left behind in TME. Up to 15% patients with rectal cancer have PSW involvement at presentation, this is associated with increased local recurrence.

Problem There are two main approaches in the management of PSW nodes. In the Western hemisphere, patients are typically staged with pre-operative MRI. Those with nodes undergo neo-adjuvant chemoradiotherapy to downstage the tumour, followed by surgical resection, PSW lymph nodes are left in place. In the East patients undergo PSW lymph node dissection at the time of rectal resection. There is evidence that lymphadenectomy at initial surgery or after chemoradiotherapy improves oncological outcome, though this is at the cost of increased morbidity, worsening urinary and sexual function.

Objective The aim is to make PSW lymph node dissection safer and more targeted. This initial feasibility study, is investigating if PSW lymph nodes can be individually identified using dual modalities, fluorescence, and a radioisotope tracer. The fluorophore indocyanine green (ICG) has been used successfully for lymph node mapping in rectal cancer. ICG and Technetium-99m nanocolloid (Tc99m), a radioisotope, have been used as dual tracers for lymph nodes in gynaecological, esophagogastric and oral surgery, but never in rectal surgery.

Method The investigators have designed an open label, single-centre, feasibility study to investigate if PSW lymph nodes can be identified intra-operatively using a radioisotope and fluorescence. Ten post neo-adjuvant chemotherapy rectal cancer patients will be scheduled for resection. Pre-operatively patients will receive an injection of Tc99m and ICG to the submucosa around the tumour. Patients will undergo single-photon emission computed tomography (SPECT) scanning to identify lymphatic drainage. Intra-operatively, after bowel resection, the surgical team will examine the PSW for lymph nodes using a minimally invasive gamma probe (SENSEI, Lightpoint Medical) to detect Tc99m, and a near infrared camera system (Firefly, Intuitive) to visualise ICG. The primary outcome is intraoperative detection of PSW lymph nodes.

Significance The aim from this feasibility study is to demonstrate that individual PSW nodes can be detected intra-operatively. By proving this technique, the investigators will design a larger study to investigate the oncological outcome of excising individual involved nodes, with the aim of reducing PSW recurrence and surgical morbidity.