Purpose Radioguided surgery has been widely used for clinical procedures such as sentinel node resections. In the (robotassisted) laparoscopic setting radioguidance is realized using laparoscopic gamma probes, which have limited maneuverability. To increase the rotational freedom, a tethered DROP-IN gamma probe was designed. Here we present the first in vivo feasibility study of this technology in prostate cancer patients. Methods Ten patients scheduled for a sentinel node procedure received four injections into the prostate with (indocyanine green-) 99mTechnetium-nanocolloid and underwent preoperative imaging (lymphoscintigraphy and SPECT/CT). The DROP-IN probe was inserted via the assistant port, still permitting the insertion and usage of additional laparoscopic tools. Results The sentinel nodes were resected using the da Vinci ® Si robot under guidance of DROP-IN gamma tracing and fluorescence imaging. The surgeon was able to independently maneuver the DROP-IN probe using the ProGrasp® forceps of the da Vinci® robot and distinguish sentinel nodes from background signal (such as the injection site). Conclusions Overall the DROP-IN design proves to be a valuable tool for robot-assisted radioguided surgery approaches.

With the rapid expansion of robot-assisted surgical procedures, the need for robot-compliant image guidance technologies has also increased. Examples hereof are the integrated firefly fluorescence camera, the drop-in ultrasound probe, and the recently introduced DROP-IN gamma probe. Combined with 68Ga–prostate-specific membrane antigen–(PSMA)–11 PET/CT (staging) and 99mTc-PSMA-I&S SPECT/CT (preoperative imaging), the latter DROP-IN gamma probe technology recently allowed us to perform the first clinical cases of robot-assisted PSMA-guided salvage surgery of lymphatic metastases.

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