Within the concept of radioguided surgery, findings in preoperative nuclear medicine imaging, e.g. scintigraphy and single-photon emission computed tomography/ computed tomography (SPECT/CT), have been successfully translated to surgery. Such radioguided resections have been explored for a range of indications, tracers and isotopes . Radioguidance is most routinely applied during sentinel lymph node (SN) identification with 99mTc-labeled radiocolloids (e.g. 99mTc-nanocolloid) . Although a wide variety of intraoperative radioguidance modalities has been studied, such as mobile gamma cameras and freehandSPECT, the gamma-ray detection probe with its acoustic and numerical feedback still remains the leading intraoperative modality .
Evolutionary developments in the field of surgery have increasingly pushed towards minimally invasive approaches such as (robot-assisted) laparoscopic surgery. This shift resulted in the development of laparoscopic gamma probes, which essentially are elongated gamma probes that can be inserted through a trocar. While numerous sites use such probes during laparoscopic SN procedures of, for example, cervical cancer and prostate cancer [2, 3], the probe length and its pivot point in the trocar greatly decrease the degrees of freedom (DOF) available for probe placement to four DOF vs. six in open surgery . This rotational impairment limits the identification of lesions (e.g. SNs generally harbor 1% of injected dose (ID)) when located in close vicinity to high background signals (e.g. during SN procedures the injection site harbors >90% of ID) [5, 6]. Additionally, blocking a trocar with this tool denies access of other tools (e.g. suction or tissue retrieval). In case of robot-assisted laparoscopic surgery, traditional radioguidance is further complicated by the fact that the surgeon is not present at the bedside, but performs surgery via the use of a distant console. Consequently, the surgical assistant has to perform gamma tracing under verbal guidance of the surgeon.
The emergence of fluorescence imaging cameras as an integrated tool during (robot-assisted) laparoscopic procedures, with the appealing real-time visual guidance they provide, is increasingly pushing surgeons away from the field of nuclear medicine. One may argue this is a potentially dangerous phenomenon given that clinical studies with hybrid tracers such as indocyanine green (ICG)-99mTc-nanocolloid, clearly indicate that fluorescence guidance cannot replace radioguidance, but rather complement it in a best-of-both-worlds scenario . Nevertheless, during robot-assisted hybrid SN procedures, the above mentioned practical limitations of the laparoscopic gamma probe increasingly diminish its use during surgery. As a result, nuclear medicine findings are used for preoperative planning, fluorescence guidance for intraoperative SN identification and the laparoscopic gamma probe is generally used as back-up and ex vivo confirmatory modality . To reintroduce the use of intraoperative radioguidance, and thus expand the market for (tracer) innovations in nuclear medicine, more practical laparoscopic gamma probe technologies need to become available.
Recently we reported on the development and preclinical evaluation of a tethered DROP-IN gamma probe technology . In this study we report on the first-in-human experience with this technology during robot-assisted laparoscopic SN procedures of the prostate.