Euromedim 2006 :1st European Conference on Molecular Imaging Technology

An Intraoperative beta probe for brain tumor surgery

11 May 2006, 14:00

1h

Palais du Pharo, Marseille

poster • New ideas Poster session : Imaging systems, Molecular Imaging

Speaker

Dr Laurent MENARD (Laboratoire Imagerie et Modélisation en Neurobiologie et cancérologie (UMR 8165) - Université Paris 7)

Description

Surgery is still considered the primary therapeutic procedure for high grade gliomas and several recent clinical studies have shown that gross total tumor resection is directly associated with longer and better survival when compared to subtotal resection. In order to refine the resection especially in the boundaries of gliomas, we are developing an intraoperative probe specifically dedicated to the localization of residual tumor labeled with positron emitters. The probe was designed to be compact and electrically safe in order to be directly coupled to the excision tool leading to simultaneous detection and removal of tumor tissues. The detection head of the intraoperative beta-probe consists of plastic scintillating fibers held in a close packed annular arrangement ensheathing the excision tool. This head is connected to an optic fiber bundle that exports the scintillating light to a multi-channel photomultiplier. The annihilation gamma ray background generated by the annihilation of beta+ in tissues is eliminated by a real-time subtraction method. Validation of the technical choice and optimization of the probe geometry were performed by preliminary measurements and Monte Carlo simulations. Simulations were realized using MCNP code and an anthropomorphic brain phantom filled with different radiotracer activities. Optimal performances were obtained with a detection head composed of 2-mm diameter and 0.5-mm long scintillating beta-sensitive fibers associated to 2-mm diameter and 2-mm long beta-shielded fibers for the gamma ray background rejection. The theoretical probe sensitivity was found to be 1.95 cps/kBq/ml with a gamma ray rejection efficiency of 99.6%. The expected minimum radiotracer detectable concentration for 18F-FET was 3.7 kBq/ml. When compared to the 10.7 kBq/ml average concentration in the bulk of the tumor, this value demonstrate the ability of the probe to define more accurately the extent of brain tumor resection. Following these results, a first prototype of the probe based on seven detection elements was developed. Characterization of the device including uniformity of the signal gain and of the beta and gamma sensitivity among the detection elements, spatial resolution and gamma ray rejection efficiency will be presented. The ability of the prototype to localize small amounts of beta+-emitting radiopharmaceuticals will be also demonstrated using a brain phantom simulating a surgical cavity after excision of the bulk of the tumor labeled with 18F.