A DROP-IN beta probe for robot-assisted (68)Ga-PSMA radioguided surgery: first ex vivo technology evaluation using prostate cancer specimens

BACKGROUND: Recently, a flexible DROP-IN gamma-probe was introduced for robot-assisted radioguided surgery, using traditional low-energy SPECT-isotopes. In parallel, a novel approach to achieve sensitive radioguidance using beta-emitting PET isotopes has been proposed. Integration of these two concepts would allow to exploit the use of PET tracers during robot-assisted tumor-receptor-targeted. In this study, we have engineered and validated the performance of a novel DROP-IN beta particle (DROP-IN(β)) detector. METHODS: Seven prostate cancer patients with PSMA-PET positive tumors received an additional intraoperative injection of ~ 70 MBq (68)Ga-PSMA-11, followed by robot-assisted prostatectomy and extended pelvic lymph node dissection. The surgical specimens from these procedures were used to validate the performance of our DROP-IN(β) probe prototype, which merged a scintillating detector with a housing optimized for a 12-mm trocar and prograsp instruments. RESULTS: After optimization of the detector and probe housing via Monte Carlo simulations, the resulting DROP-IN(β) probe prototype was tested in a robotic setting. In the ex vivo setting, the probe—positioned by the robot—was able to identify (68)Ga-PSMA-11 containing hot-spots in the surgical specimens: signal-to-background (S/B) was > 5 when pathology confirmed that the tumor was located < 1 mm below the specimen surface. (68)Ga-PSMA-11 containing (and PET positive) lymph nodes, as found in two patients, were also confirmed with the DROP-IN(β) probe (S/B > 3). The rotational freedom of the DROP-IN design and the ability to manipulate the probe with the prograsp tool allowed the surgeon to perform autonomous beta-tracing. CONCLUSIONS: This study demonstrates the feasibility of beta-radioguided surgery in a robotic context by means of a DROP-IN(β) detector. When translated to an in vivo setting in the future, this technique could provide a valuable tool in detecting tumor remnants on the prostate surface and in confirmation of PSMA-PET positive lymph nodes.