Abstract
658
Objectives: This first-in-men study evaluates 68Ga-PSMA for intraoperative assessment of tumor margins at time of robot-assisted radical prostatectomy, aided by Cerenkov Luminiscence Imaging (CLI).
Methods: 3-4 hours prior to surgery, PSMA-PET/CT was performed after intravenous injection of 68Ga-PSMA. Scan results were assessed by the specialists of nuclear medicine and urology. Radical prostatectomy was performed robotically and the prostate specimen was imaged with a CLI imager (Lightpoint Medical Ltd, UK) intraoperatively immediately after excision with mean measurement of the radiance on the surface. The agreement of margin distance on histopathology and CLI was assessed.Two specimens were measured in an Hyper-Pure Germanium detector to access the nominal radioactivity amount at the time of radical prostectomy. Results: CLI was used in five patients after preoperative injection of 144±39 MBq (mean ± standard deviation, range: 95-202 MBq) 68Ga-PSMA. Intraprostatic lesions were detected by PSMA-PET/CT in 100%, positive lymph nodes could be seen in 3 of 5 patients. CLI was performed intraoperatively after a mean of 329 minutes after tracer injection. Mean background radiance of the prostate was 1441 photons/s/cm2/sr. Positive surgical margins were found in two patients based on histopathology (patient 1: pT3b, pN1, Gleason score 5+3=8, patient 2: pT3a, pN1, Gleason score 4+5=9). In these patients, elevated radiance levels were found in the tumor positive areas mean radiance: 4254 photons/s/cm2/sr.The two measured prostate specimens contained 2.3 and 10.6 kBq (decay corrected to the time of prostate excision). Conclusions: 68Ga-PSMA CLI seems to be a promising technique for intraoperative assessment of surgical margins in robot-assisted radical prostatectomy. Under the current study design, prostate removal is below the regulated limit (1 MBq 68Ga) and occupational exposure is kept at reasonable minimum. A prospective trial is mandatory to elucidate further results concerning sensitivity, specificity and radiation safety.
