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Radio Guided Surgery (RGS) is a nuclear medicine technique allowing the surgeon to identify tumor residuals in real time with a millimetric resolution, thanks to a radiopharmaceutical as tracer and a probe as detector. The use of beta(-) emitters, instead of gamma or beta(+), has been recently proposed with the aim to increase the technique sensitivity and reducing both the administered activity to the patient and the medical exposure. In this paper, the possibility to use the commercial CMOS Image Sensor MT9V115, originally designed for visible light imaging, as beta(-) radiation detector RGS is discussed. Being crucial characteristics in a surgical environment, in particular its stability against time, operating temperature, integration time and gain has been studied on laboratory measurements. Moreover, a full Monte Carlo simulation of the detector has been developed. Its validation against experimental data allowed us to obtain efficiency curves for both beta and gamma particles, and also to evaluate the effect of the covering heavy resin protective layer that is present in the "off the shelf" detector. This study suggests that a dedicated CMOS Image Sensor (i.e. one produced without the covering protective layer) represents the ideal candidate detector for RGS, able to massively increase the amount of application cases and the efficacy of this technique.

The recent interest in beta- radionuclides for radio-guided surgery derives from the feature of the beta radiation to release energy in few millimeters of tissue. Such feature can be used to locate residual tumors with a probe located in its immediate vicinity, determining the resection margins with an accuracy of millimeters. The drawback of this technique is that it does not allow to identify tumors hidden in more than few mm of tissue. Conversely, the bremsstrahlung X-rays emitted by the interaction of the beta- radiation with the nuclei of the tissue are relatively penetrating. To complement the beta- probes, we have therefore developed a detector based on cadmium telluride, an X-ray detector with a high quantum efficiency working at room temperature. We measured the secondary emission of bremsstrahlung photons in a target of Polymethylmethacrylate (PMMA) with a density similar to living tissue. The results show that this device allows to detect a 1 ml residual or lymph-node with an activity of 1 kBq hidden under a layer of 10 mm of PMMA with a 3:1 signal to noise, i.e. with a five sigma discrimination in less than 5 s.

Spatial localization of radioactive sources is currently a main issue interesting different fields, including nuclear industry, homeland security as well as medical imaging. It is currently achieved using different systems, but the development of technologies for detecting and characterizing radiation is becoming important especially in medical imaging. In this latter field, radiation detection probes have long been used to guide surgery, thanks to their ability to localize and quantify radiopharmaceutical uptake even deep in tissue. Radiolabelled colloid is injected into, or near to, the tumor and the surgeon uses a hand-held radiation detector, the gamma probe, to identify lymph nodes with radiopharmaceutical uptkake. The present work refers to a novel scintigraphic goniometric probe to identify gamma radiation and its direction. The probe incorporates several scintillation crystals joined together in a particular configuration to provide data related to the position of a gamma source. The main technical characteristics of the gamma locator prototype, i.e. sensitivity, spatial resolution and detection efficiency, are investigated. Moreover, the development of a specific procedure applied to the images permits to retrieve the source position with high precision with respect to the currently used gamma probes. The presented device shows a high sensitivity and efficiency to identify gamma radiation taking a short time (from 30 to 60 s). Even though it was designed for applications in radio-guided surgery, it could be used for other purposes, as for example homeland security.

P-terphenyl crystals are high light yield organic scintillators characterised by a relatively short intrinsic light attenuation length. The effective value of this physical quantity depends on the actual design of the detector and can be tuned for a specific application with the appropriate combination of crystal size and shape, its bulk and superficial optical properties and the light sensor choice. In this paper we investigate the feasibility to use this feature to realize a simple, mono crystal, position sensitive, β− particle counter able to identify both the presence and the position of a β− point source located in close proximity of the detector. This simple design allows an integration of this detection technique into specific β−-RGS (Radio Guided Surgery) surgical devices of use in brain tumour-ectomy and in endoscopic applications, giving the surgeon a better guidance to spot the tumour localisation. We present the results obtained with two devices: a single channel particle counter built on a cylindrical crystal (=10 mm, h=10 mm) designed to probe and identify the position of a point β− source located around the surface of the detector, and a four channels particle counter built on a smaller (=7 mm, h=3 mm), ring shaped, crystal designed to identify the position of a point β− source placed just ahead of the detector. In both configurations we were able to clearly identify the presence and the position, relative to the detector, of a radio-active point source set off axis with respect to the crystal. The four channel detector shows an angular resolution of ±8 degree and an effective light absorption length of 4.2±0.1 mm. The single channel cylindrical crystal have a 8.0±0.5 mm effective light absorption length and the same discovery potential.

Radio-Guided Surgery enables the surgeon to identify tumor residuals in real time, with millimetric resolution. This technique takes advantage of a radiopharmaceutical as tracer and a probe as detector. The employment of β− emitters as tracers, instead of γ or β+, reduces the background from the healthy tissues and the medical exposition risk. The performances of a CMOS sensor, the MT9V011, originally designed for visible light imaging, as β− radiation detector have been investigated. In particular, we have studied the impact of an infra-red filter placed in front of the sensor in the existing commercial devices, and we have determined the sensitivity and spatial resolution of the sensor, in the presence of a localized ionization source of variable size. Finally, by evaluating the sensitivity to clinical-like activities and geometries we conclude that even with the small size of the sensor, that can potentially be increased, the acquisition time required to discriminate a tumor residual from healthy tissues is of a few seconds for transverse dimensions greater than 3 mm.

In case of lymphatic cancers, the sentinel lymph node technique is performed using a gamma probe for intraoperative radioguided surgery. The inorganic scintillating crystal gamma probe developed at IPHC was equipped with 4 fast decay time inorganic scintillators: YAP, LYSO, LaCl3 and LaBr3. Energy resolutions are compared experimentally with single photon radioisotopes for small crystal cylinders (4 mm diameter, 12 mm length). The 6.1% measured energy resolution at 511 keV demonstrates the great advantage to use the high photon yield LaBr3 crystal for detection of γ-ray coming from positron annihilation using β+ radiomarked molecules.

著者人数: 11名, Accepted: 2013-05-02, 資料番号: SA1004632000