M. Bruzzi, Sviluppo di sistemi di rivelazione a silicio per imaging con protoni e dosimetria Sviluppo di sistemi di rivelazione a silicio per imaging con protoni e dosimetria M. Bucciolini a,b, M. Bruzzi b,c, D. Menichelli b,c, C. Talamonti a,b, M. Brianzi b, L. Marrazzo b,g, S. Pallotta a,b, M. Tesi c, C.Civinini b, G. Candiano f, G. A. P. Cirrone f, G. Cuttone f, D. Lo Presti d,e, N. Randazzo e, V.Sipala d,e a) Dipartimento di Fisiopatologia Clinica, Università degli Studi di Firenze. b) INFN, sezione di Firenze. c) Dipartimento di Energetica, Università degli Studi di Firenze. d) Dipartimento di Fisica, Università degli Studi di Catania. e) INFN, sezione di Catania. f) Laboratori Nazionali del Sud-INFN, Catania. g) Azienda Ospedaliero-Universitaria Careggi, Firenze

M. Bruzzi, Sviluppo di sistemi di rivelazione a silicio per imaging con protoni e dosimetria 1. Proton Computed Tomography Advantages of hadron-therapy with respect to conventional gamma - X ray therapy: i) lower dose to healthy tissues in front of the tumor; ii) healthy tissues beyond the tumor are not damaged; iii) Multiple scattering for protons is small enough that a very sharp dose profile can be maintained. Lateral healthy tissues are not damaged. The stopping power distributions are the main parameters for dose calculation in hadron therapy. They are derived from measured attenuation coefficients μ of conventional XCT But protons and photons interact differently with matters... “The error intrinsic in this conversion (due to m(he,Z) dependency on atomic number and electron density) is the principal cause of proton range indetermination (3%, up to 10 mm in the head).” Schneider U. (1994), Med Phys. 22, 353.

M. Bruzzi, Sviluppo di sistemi di rivelazione a silicio per imaging con protoni e dosimetria INFN V Commission

M. Bruzzi, Sviluppo di sistemi di rivelazione a silicio per imaging con protoni e dosimetria

Projection of the map along y axis. A Gaussian fit of the main component is superimposed to the plot. Number of protons crossing a given x-y position. Position given in terms of strip index (strip pitch is 200  m). Collimator diameter is 5.0mm.  V th =200mV

M. Bruzzi, Sviluppo di sistemi di rivelazione a silicio per imaging con protoni e dosimetria Projection of data along y axis. The histogram of events triggered by crystal IV (II) is plotted with a black (red) solid line. Map of events triggered by crystals II (red) and IV (black).  V th =200mV, E=62MeV. The collimator was removed from the beam pipe.

M. Bruzzi, Sviluppo di sistemi di rivelazione a silicio per imaging con protoni e dosimetria 2. Development of a 2D Silicon dosimeter MAESTRO - Integrated Project (VI Framework program) Develop a device adequate for 2D pre-treatment in phantom dose verifications in conformal radiotherapy as photon Intensity Modulated Radio Therapy (IMRT). Accurate determination of the 2D absorbed dose distribution requires detectors with high spatial resolution, a response independent of the dose rate, of the energy, fast, stable in time, with a good linearity, high dynamic range and radiation hardness. TPS IMRT prosthate GTV = gross target volume CTV = clinical target volume = gTV + margini PTV planning target volume = cTV + margini Sezione assiale del corpo

M. Bruzzi, Sviluppo di sistemi di rivelazione a silicio per imaging con protoni e dosimetria Geometry of the 441 channels Si module. Silicon segmented sensor, n-type implant on an epitaxial p-type layer. Each element is 2x2 mm 2 and the distance center-to-center is 3 mm. The sensor is composed of 21x21 pixels. Area 6.29x6.29 cm 2. Detector Details of the TERA06 chips and wedge-bonding connections between the printed circuit board and the silicon module.

M. Bruzzi, Sviluppo di sistemi di rivelazione a silicio per imaging con protoni e dosimetria Overview of the large scale detector design. Large-Scale Design Details of connection between the kapton flexible circuit (pale green) and central silicon module.

M. Bruzzi, Sviluppo di sistemi di rivelazione a silicio per imaging con protoni e dosimetria Radiation Hardness A straightforward improvement of the efficiency and long term stability of silicon dosimeters has been obtained with an n + -p junction surrounded by a guard-ring structure implanted on an epitaxial 50  m p-type Si layer grown on a Czochralski substrate. M. Bruzzi, M. Bucciolini, M. Casati, D. Menichelli, C. Talamonti, C. Piemonte, "Epitaxial Si dosimeters for radiotherapy applications," Appl. Phys. Lett., 2007

M. Bruzzi, Sviluppo di sistemi di rivelazione a silicio per imaging con protoni e dosimetria Results Almost all the channels exhibit a repeatability < 0.5%, reproducibility < 1% deviation from linearity is 0.3% in the dose range cGy, and the fraction of channels which have a deviation better than 1% is 98% Measurements in the dose rate range cGy/min indicate that there is no dose rate dependence. Mean sensitivity = ± nC/cGy The energy dependence for assessed for different beam quality and TPR were measured at different depths. As expected a slight energy dependence was observed since silicon is not water equivalent

M. Bruzzi, Sviluppo di sistemi di rivelazione a silicio per imaging con protoni e dosimetria Profile along the central column for different field size ( 0.8X0.8, 1.6x1.6, 2.4x2.4, 3.2x3.2, 4x4, 4.8x4.8 ) Signal (C) Dose maps Profiles 6MV photon beam at Careggi Hospital

M. Bruzzi, Sviluppo di sistemi di rivelazione a silicio per imaging con protoni e dosimetria Depth dose measurements (protons) CATANA: 62 MeV proton beam Measurements in PMMA Signal normalized at 12.5 mm Spread Out Bragg Peak

M. Bruzzi, Sviluppo di sistemi di rivelazione a silicio per imaging con protoni e dosimetria IMRT Field Inserire mappa focus 10MV photon beam at Careggi Hospital

M. Bruzzi, Sviluppo di sistemi di rivelazione a silicio per imaging con protoni e dosimetria

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M. Bruzzi, Sviluppo di sistemi di rivelazione a silicio per imaging con protoni e dosimetria Trasparenze di appoggio

M. Bruzzi, Sviluppo di sistemi di rivelazione a silicio per imaging con protoni e dosimetria

TPR measurements (photons) For the same beam quality, detector centered at the isocentre, the TPR(d,5) have been measured and compared with ionization chamber. 6MV photon beam at Careggi Hospital

M. Bruzzi, Sviluppo di sistemi di rivelazione a silicio per imaging con protoni e dosimetria

Output factors (protons) Measurement performed at Catania

M. Bruzzi, Sviluppo di sistemi di rivelazione a silicio per imaging con protoni e dosimetria Output factors (photon) These good results have been obtained resolving packaging problems Measurement performed at IBA site

M. Bruzzi, Sviluppo di sistemi di rivelazione a silicio per imaging con protoni e dosimetria Angular dependence Measurement performed at IBA site

M. Bruzzi, Sviluppo di sistemi di rivelazione a silicio per imaging con protoni e dosimetria

Publications and dissemination A patent has been deposited: Italian patent No. FI2006A000166, 30 June 2006, University of Florence, Inventors: M. Bruzzi, M. Bucciolini, D. Menichelli, C. Talamonti. International patent application No. PCT/IB2007/ M. Casati, M. Bruzzi, M. Bucciolini, D. Menichelli, M. Scaringella, C. Piemonte and E. Fretwurst, ”Characterization of standard and oxygenated float zone Si diodes under radiotherapy beams"Nuclear Instruments and Methods in Physics ResearchA, 552, (2005) M. Bruzzi, M. Bucciolini, M. Casati, D. Menichelli, C. Talamonti, C. Piemonte, B. G. Svensson: "Epitaxial silicon devices for dosimetry applications”, Applied Physics Letters 2007, 90, D. Menichelli, M. Brianzi, M. Bruzzi, M. Bucciolini, M. Casati, A. De Sio, L. Marrazzo, C. Piemonte, C. Talamonti, M. Tesi:” Design and development of a silicon segmented detector for 2D dose measurements in radiotherapy”, Nuclear Instruments and Methods in Physics ResearchA, 583, (2007) C. Talamonti, M. Bucciolini, M. Bruzzi, L. Marrazzo, D. Menichelli.:“Preliminary dosimetric characterization of a silicon segmented detector for 2D dose verifications in radiotherapy“,Nuclear Instruments and Methods in Physics Research A, 583, ( 2007), pp C. Talamonti, M. Bucciolini, M. Bruzzi, L. Marrazzo, D. Menichelli.:“Dosimetric characterization with 62 MeV protons of a silicon segmented detector for 2D dose verifications in radiotherapy,Nuclear Instruments and Methods in Physics Research A, 596 ( 2008), pp

M. Bruzzi, Sviluppo di sistemi di rivelazione a silicio per imaging con protoni e dosimetria Carrier lifetime decreases with dose due to the creation of generation- recombination centers. To mitigate the sensitivity decrease with the accumulated dose, commercially available Si diodes are usually pre-irradiated up to about 10 kGy with high energy electrons. After this pre-irradiation, a further, less pronounced, decay in sensitivity is still observed. For this reason, the hospital use of silicon dosimeters requires a frequent recalibration, which represents a serious drawback. Sensitivity S is proportional to the active volume V and largely determined by the minority carrier diffusion length L. The sensitivity degradation is thus related to the decrease of the minority carrier lifetime  ( L = (D  ) 1/2 with D diffusion constant). G.Rikner and E.Grusell, Effects of Radiation damage on p-type silicon detectors, Phys. Med. Biol. 1983, 28, 11,

M. Bruzzi, Sviluppo di sistemi di rivelazione a silicio per imaging con protoni e dosimetria Dose rate dependence (photons) The dose rate has been changed varying both the pulse repetition frequency (data set A) and both PRF and SSD, i.e. the dose per pulse (data set B). 6MV photon beam at Careggi Hospital Comparison of relative dose measured with the Si dosimeter and a Farmer ionization chamber. 60 Co source beam at Lucca Hospital