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18/12/13 prof. Dr. Marcos Alvarez (USP)

Título: Silicon Strip Detectors: From Nuclear Reactions to Medical Applications

Resumo: In complex radiation therapy treatments with photons, such as Intensity Modulated Radiation Therapy (IMRT), dose distribution verification is highly advisable prior to real dose delivery to patient. In fact, the increasing sophistication and complexity of IMRT treatments is a major challenge for Treatment Planning Systems (TPS). This seminar presents the development of a new detection system for IMRT treatment verification, based on single sided silicon strip detectors (SSSSD), which are traditionally and successfully used to measure nuclear reaction products [1, 2]. In our system, the SSSS detector is placed inside a cylindrical phantom, which simulates the human body, with the detector plane positioned perpendicular to the symmetry axis of such cylinder, and parallel to the radiation beam axis. The system is irradiated by a Siemens Primus LINAC, operating at 6MV photon mode, at a Hospital. This allows to obtain dose maps, in axial planes, which are the most relevant in the process of treatment planning since they correspond, in general, to Computed Tomography (CT) slices of the patient. This is the main innovation with respect to other recently developed systems, based on diode or ionization chamber arrays. Within our novel setup, either the cylindrical phantom or the LINAC can rotate and data are taken for different relative orientations between the detectors strips and the radiation fields, allowing measurements cross check. New software has been developed to operate the rotation of the phantom and to acquire the signals from the silicon strip detectors. The dose maps are calculated from the set of data recorded for a certain sequence of relative orientations, using a reconstruction algorithm similar to the CT ones. This work is on the frame of a scientific collaboration between the National Accelerator Centre (CNA), the University Hospital “Virgin Macarena”, the private company “Instalaciones Inabensa S. A.” and the University of Seville, in Seville, Spain. A patent application of this procedure has been submitted to the Spanish Office of Patents (expedient nº P201101009). Finally, the novel method has been published in different international reviews [3-6].

References: 
[1] Physical Review Letters 109, 262701 (2012); 
[2] Physical Review Letters 110, 142701 (2013); 
[3] Progress in Nuclear Science and Technology, Vol. 2, pp. 191-196 (2011); 
[4] Radiotherapy and Oncology, vol. 99, suppl. 1, p. S172 (2011); 
[5] Nuclear Instruments and Methods A: Accelerators, Spectrometers, Detectors and Associated Equipment – NIM A 673 (2012) 98-106; 
[6] Physical Review Special Topics: Accelerators and Beams 15, 042802 (2012).