A novel radioguided surgery technique exploiting β(-) decays

Abstract

The background induced by the high penetration power of the radiation is the main limiting factor of the current radio-guided surgery (RGS). To partially mitigate it, a RGS with β(+)-emitting radio-tracers has been suggested in literature. Here we propose the use of β(-)-emitting radio-tracers and β(-) probes and discuss the advantage of this method with respect to the previously explored ones: the electron low penetration power allows for simple and versatile probes and could extend RGS to tumours for which background originating from nearby healthy tissue makes probes less effective. We developed a β(-) probe prototype and studied its performances on phantoms. By means of a detailed simulation we have also extrapolated the results to estimate the performances in a realistic case of meningioma, pathology which is going to be our first in-vivo test case. A good sensitivity to residuals down to 0.1 ml can be reached within 1 s with an administered activity smaller than those for PET-scans thus making the radiation exposure to medical personnel negligible.

Figure 1. The radioguided surgery technique (RGS).

Steps of the procedure: (1) a radio-labelled tracer is administered to the patient, before the surgery; (2) the emitting tracer is preferentially taken up by the tumour; (3) after the cancerous bulk removal, the surgeon explores the lesion with a radiation detecting probe and looks for targeted tumour residuals in real time. The bottom boxes show the effect of the proposed replacement of the -emitting tracers (a) with electron-emitting tracers (b). Due to the high penetration power of the photons, in the first case a non-negligible background can be produced by the healthy organs close to the lesion, sometimes preventing the applicability of the technique. To mitigate this effect a shielding or active veto is applied (see inset of box a) thus making the probes cumbersome. Electrons, instead, provide a clearer delineation of radioactive tissue's margins allowing for a simple and compact probe and requiring a smaller radio-pharmaceutical activity. [Figure drawn by S.M. and E.S.C.].

Figure 2. First prototype of the intraoperative β⁻ probe.

The core is a cylindrical scintillator (diameter 2.1 mm, height 1.7 mm) of poli-crystalline p-terphenyl. A ring of PVC wraps the scintillator and shields it against radiation coming from the sides. The device is encapsulated inside an easy-to-handle aluminum body as protection against mechanical stress and it is protected against light by a thin PVC layer.