Back-table specimen scanning using gantry-free hybrid hSPECT/LiDAR imaging: a feasibility study during PSMA-radioguided surgery.

Introduction: Prostate-specific membrane antigen (PSMA) targeted precision surgery is becoming increasingly popular. However, the relatively low levels of PSMA-receptor expression and background signal can hinder in vivo lesion detection and margin evaluation. Back-table imaging (ex vivo) potentially provides a means to confirm surgical accuracy. For Tc-PSMA-radioguided surgery, an innovative gantry-free hybrid imaging technique has recently been proposed, namely handheld single-photon emission computed tomography (hSPECT) combined with light detection and ranging (LiDAR). This study aimed to assess the feasibility and performance of hSPECT/LiDAR in analyzing tissue specimens excised after robotic Tc-PSMA-radioguided surgery.

Methods: We included samples from 5 prostate cancer patients undergoing primary or salvage robot-assisted resection of Tc-PSMA-I&S avid lesions that were identified using a drop-in gamma probe. 12 samples (1 prostatic tissue, 1 local recurrence tissue, 10 lymph nodes) were analyzed ex vivo using a custom-built specimen tray, including an optical reference tracker for scan registration. LiDAR was used to acquire a surface scan of the specimens, and the 3D OBJ image output was fused with the 3D DICOM of a hSPECT obtained using a handheld gamma camera and DeclipseSPECT tracking system.

Results: hSPECT/LiDAR imaging provided accurate representation of the Tc-PSMA-I&S uptake within the specimens. In 8 samples, it helped to confirm a true positive lesion. In the remaining 4 samples, non-visualization aligned with negative histopathology (true negative). A strong correlation was found between PSMA-hSPECT/LiDAR and PSMA-PET/CT (p < 0.05), but no correlation could be established with PSMA-SPECT/CT (p = 0.515). The count rates fount in the scan correlated to tumor size (p = 0.016) and were not influenced by the overall specimen's size (p = 0.558).

Conclusion: We present the technical feasibility of a new 3D hybrid modality (hSPECT/LiDAR) that allows back-table assessment of surgical specimens from the already well validated robotic Tc-PSMA-radioguided surgery workflow.