Redefining robotic image-guidance – tomographic visualization of lesions during prostate cancer surgery via gantry-free robotic SPECT

Purpose The introduction of the drop-in gamma probe has advanced intraoperative molecular imaging during prostate cancer surgery. We have been able to convert the sensor’s numeric readout to tomographic images, so-called robotic-SPECT ( Robo SPECT) and investigate how this is impacted by radiopharmaceutical avidities and drop-in scan metrics. Methods The gamma sensor readout was registered with its 3D position and orientation, allowing a custom reconstruction algorithm to generate Robo SPECT images. Evaluations occurred in 21 patients; 10 sentinel node procedures (SN; primary prostate cancer) and 11 PSMA-radioguided surgery (recurrent prostate cancer). Robo SPECT findings were related to respective pre- and intra-operative controls, including preoperative PSMA-PET/CT and/or SPECT/CT images and fluorescence detection (SN only). Results Robo SPECT proved to be safe and applicable in a range of conditions. In the SN-group, 26 SN-SPECT/CT lesions were successfully identified with SN- Robo SPECT (100%); 3 were tumor positive (sensitivity 100%). Only 73% of SNs were surgically visible with fluorescence imaging. For the PSMA guided group, the 14 lesions identified on PSMA-PET/CT were all visualized with PSMA- Robo SPECT (100%); 18 specimens were tumor positive (sensitivity 78% for both PSMA-PET/CT and PSMA- Robo SPECT). Preoperative PSMA-SPECT/CT only identified 4 PSMA-lesions (29%). No false positives were seen for robo SPECT and all final resection margins were clean. At 6-months 0% of the SN-patients and 20% of PSMA-patients showed biochemical recurrence. Conclusion Robo SPECT provides 3D context that extends the utility of drop-in gamma tracing and assists the alignment between pre- and intra-operative target perception. Here SN- Robo SPECT clearly outperformed fluorescence SN imaging and PSMA- Robo SPECT outperformed preoperative PSMA-SPECT/CT imaging.