Abstract
1310
Background: 99mTechnetium (99mTc) based PSMA-radioguided surgery (99mTc-PSMA I&S) has proven to be a valuable tool for the intraoperative detection of prostate cancer (PCa) recurrences during open salvage surgery. However, developments in the field of PCa surgery have increasingly pushed towards minimally invasive approaches such as robot-assisted surgery.
Objectives: To describe and evaluate the technique, feasibility and short-term outcomes of robot-assisted 99mTc-based PSMA-radioguided surgery (99mTc-PSMA I&S) in recurrent PCa.
Methods: Ten consecutive patients (median PSA 0.97 ng/ml) with evidence of a single PSMA-avid PCa recurrence (either nodal or local) on diagnostic PSMA PET/CT were included in this prospective study. Following intravenous administration of 99mTc-PSMA I&S (median activity 539 MBq, interquartile range [IQR] 533-562), all patients received an additional pre-operative whole-body SPECT/CT (approximately 17 h post-injection) serving mainly as a quality control for tracer injection and distribution. Differences between the PSMA PET and SPECT scans were examined. At 21 h post-injection, robot-assisted radioguided resections were realized using the tethered DROP-IN gamma probe. Radioactive ratings (positive vs. negative) in vivo and in resected tissue (back table examination) were compared with histopathological analysis. Tissue was rated positive when the count rate was at least twice the background (fatty tissue) count rate. The frequency of > 50% PSA reduction and complete biochemical response (cBR; PSA < 0.2 ng/ml) at six weeks after surgery was recorded. Results: Compared to the diagnostic PSMA PET/CT, the SPECT/CT scans were able to visualize only 70% of the lesions. Nevertheless, using the DROP-IN gamma probe all preoperatively identified lesions (median metastatic size at pathology 8 mm, range 3-50 mm) could be localized and resected. In vivo, the count rate in metastatic tissue and benign tissue was 128 counts/s (IQR 91-192 and 40 counts/s (IQR 32-68) and) respectively, corresponding to a median tumor-to-background ratio of 1.8 (IQR 1.6-2.3). On ex vivo measurements, the count rate in metastatic and (fatty) background tissue was 151 counts/s (IQR 71-266.8) and 6 counts/s (IQR 4-8) respectively, resulting in a median tumor-to-background ratio of 21 (IQR 8.3-29.6). One nodal recurrence (diameter 3 mm) was not detected with 99mTc-PSMA I&S nor by preoperative PSMA PET/CT. Combined this resulted in a sensitivity and specificity of 91% and 100%, respectively. Postoperative PSA measurements were available for seven patients. A > 50% PSA reduction and a cBR was achieved in 4 (57%) and 2 (29%) patients respectively. Two patients (28%) reported a Clavien-Dindo grade 1 complication related to surgery.
Conclusions: Using the DROP-IN gamma probe it has been possible to translate 99mTc-PSMA-radioguided surgery to the robotic setting. This is the next step in minimally invasive surgery that enables the intraoperative detection and removal of recurrent PCa lesions with high diagnostic accuracy. The long-term impact on outcome has yet to be evaluated.