Radio-guided surgery with β− radiation: tests on ex-vivo specimens

Radio-Guided Surgery (RGS) is a surgical technique aimed at assisting the surgeon to reach as complete a resection of the tumoural lesion as possible. Established methods to date make use of γ -emitting tracers to radio-mark the neoplastic tissue. However, in case of uptake from healthy organs around the lesion the large penetration of photons yields a non-negligible background that can limit the RGS application. The adoption of β− radiation has been proposed to overcome this limit. To validate the entire RGS procedure, from the evaluation of the tracer uptake of the tumor, to the assumptions on the bio-distribution and the signal detection, tests on ex vivo specimens of meningioma brain tumour were performed. Meningioma was selected due to the well known high receptivity to a β− emitting radio-tracer already in use in the clinical practice: 90Y-labelled DOTATOC. Patients were enrolled according to the tumour Standard Uptake Value (SUV > 2) and the expected Tumour to Non-tumour Ratio (TNR > 10) estimated from 68Ga-DOTATOC PET images. After injecting the patients with 93–167, MBq of 90Y - DOTATOC, 26 samples excised during surgery were examined with a dedicated β− detecting probe to assess the sensitivity of millimetre-sized tumour remnants in case of administration of low activity value compatible with those injected for diagnostic exams. Even injecting as low as 1.4, MBq/kg of radio-tracer, tumour remnants greater than 0.06, ml would be discriminated by the healthy tissue in few seconds.