Freehand SPECT Combined with 3-Dimensional Light Detection and Ranging as Alternative Means of Specimen Scanning During Prostate Cancer Surgery

Prostate-specific membrane antigen (PSMA) has rapidly been established as a target for prostate cancer management for diagnosis, staging, and image-guided therapy (1,2). Nonetheless, during de novo [^99mTc]Tc-PSMA radioguided surgery, it is challenging to assess primary tumor margins. Recently, a solution has been proposed using small-bore 3-dimensional PET/CT (3,4).

Here, we report the case of a de novo prostate cancer patient scheduled for robot-assisted [^99mTc]Tc-PSMA-I&S radioguided surgery (531 MBq intravenously the day before surgery). The NCI-AvL institutional review board approved this study (IRBdm24-249). The morning of surgery, preoperative SPECT/CT (Fig. 1A) displayed elevated tracer uptake within the primary tumor site and in a suspected lymph node. After resection and without further tissue preparation, the prostate was scanned with an industrial 3-dimensional surface scanner (light detection and ranging [LiDAR]) and freehand SPECT (5). To allow synchronization of the signal and the detector orientation, the latter approach used an optically tracked crystal gamma camera (Fig. 1B). A 3-mm pixel spacing, an iterative reconstruction algorithm (maximum-likelihood expectation maximization, 20 iterations), and a 3-mm gaussian filter were used. The LiDAR scan and the molecular freehand [^99mTc]Tc-PSMA SPECT, approximately taking 3 min each, were automatically fused via an asymmetrical refence tracker. Visualization and analysis occurred in 3DSlicer software, taking 3–4 min for the elaborate image display, providing a hybrid scan in either augmented or virtual reality (Fig. 1C). The prostate specimen scan could anatomically be related to the excised prostate tissue (Fig. 1D) and the [^99mTc]Tc-PSMA uptake related to SPECT/CT findings (Fig. 1A). With SPECT intensity thresholds set at 16% of the maximum signal, margins did not display tumor involvement (Fig. 1D); at histopathology, bilateral adenocarcinoma was found in the prostate extending to extraprostatic tissue (posterolateral left region) and the left seminal vesicle (Gleason score of 4 + 5 = 9).

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FIGURE 1.

(A) [^99mTc]Tc-PSMA SPECT/CT axial images showing focal bilateral uptake in prostate, more intense on the left (yellow arrows), and in left deep obturator node (red arrow). (B) Back-table specimen scanning setup, highlighting specimen tray with integrated optical reference trackers, 3-dimensional surface scanner (0.5-mm resolution, Artec Eva [Artec3D], LiDAR), and hand-held γ-camera (CrystalCam [Crystal Photonics]) combined with DeclipseSPECT (SurgicEye). (C) Hybrid freehand SPECT/LiDAR specimen scans indicating 2 hotspots in prostate (arrows). (D) Correlated images showing (top) histopathology of primary tumor (prostate cancer) and (bottom) excised prostate tissue.

This case shows that hybrid freehand SPECT/LiDAR prostate cancer specimen imaging is feasible, thus providing a low-cost and low–radiation-dose alternative to postoperative PET scanning. Further studies are needed to define optimal threshold levels and to investigate how specimen imaging impacts the surgical procedure.

• © 2024 by the Society of Nuclear Medicine and Molecular Imaging.

• Received for publication June 17, 2024.
• Accepted for publication September 19, 2024.