Sviluppo di sistemi di rivelazione a silicio per

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

Sviluppo di sistemi di rivelazione a silicio per imaging con protoni e dosimetria M. Bucciolinia, b, M. Bruzzib, c, D. Menichelli b , c , C. Talamontia, b, M. Brianzib, L. Marrazzob, g, S. Pallottaa, b, M. Tesic, C. Civininib, G. Candianof, G. A. P. Cirronef, G. Cuttonef, D. Lo Prestid, e, N. Randazzoe, V. Sipalad, 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

1. Proton Computed Tomography Advantages of hadron-therapy with conventional gamma - X ray therapy:

1. Proton Computed Tomography Advantages of hadron-therapy with conventional gamma - X ray therapy: respect to 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.

INFN V Commission

INFN V Commission

Number of protons crossing a given x-y position. Position given in terms of strip

Number of protons crossing a given x-y position. Position given in terms of strip index (strip pitch is 200 mm). Collimator diameter is 5. 0 mm. DVth=200 m. V Projection of the map along y axis. A Gaussian fit of the main component is superimposed to the plot.

Map of events triggered by crystals II (red) and IV (black). DVth=200 m. V,

Map of events triggered by crystals II (red) and IV (black). DVth=200 m. V, E=62 Me. V. The collimator was removed from the beam pipe. Projection of data along y axis. The histogram of events triggered by crystal IV (II) is plotted with a black (red) solid line.

2. Development of a 2 D Silicon dosimeter MAESTRO - Integrated Project (VI Framework

2. Development of a 2 D Silicon dosimeter MAESTRO - Integrated Project (VI Framework program) Develop a device adequate for 2 D pre-treatment in phantom dose verifications in conformal radiotherapy as photon Intensity Modulated Radio Therapy (IMRT). Accurate determination of the 2 D 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 Sezione assiale del corpo GTV = gross target volume CTV = clinical target volume = g. TV + margini PTV planning target volume = c. TV + margini

Detector Silicon segmented sensor, n-type implant on an epitaxial p-type layer. Each element is

Detector Silicon segmented sensor, n-type implant on an epitaxial p-type layer. Each element is 2 x 2 mm 2 and the distance center-to-center is 3 mm. The sensor is composed of 21 x 21 pixels. Area 6. 29 x 6. 29 cm 2. Geometry of the 441 channels Si module. Details of the TERA 06 chips and wedge-bonding connections between the printed circuit board and the silicon module.

Large-Scale Design Overview of the large scale detector design. Details of connection between the

Large-Scale Design Overview of the large scale detector design. Details of connection between the kapton flexible circuit (pale green) and central silicon module.

Radiation Hardness A straightforward improvement of the efficiency and long term stability of silicon

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 mm 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

Results Almost all the channels exhibit a repeatability < 0. 5%, reproducibility < 1%

Results Almost all the channels exhibit a repeatability < 0. 5%, reproducibility < 1% • deviation from linearity is 0. 3% in the dose range 10 -550 c. Gy, and the fraction of channels which have a deviation better than 1% is 98% • Measurements in the dose rate range 40 -350 c. Gy/min indicate that there is no dose rate dependence. Mean sensitivity = 1. 248 ± 0. 004 n. C/c. Gy • 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

6 MV photon beam at Careggi Hospital Profiles Signal (C) Dose maps Profile along

6 MV photon beam at Careggi Hospital Profiles Signal (C) Dose maps Profile along the central column for different field size (0. 8 X 0. 8, 1. 6 x 1. 6, 2. 4 x 2. 4, 3. 2 x 3. 2, 4 x 4, 4. 8 x 4. 8)

Depth dose measurements (protons) Spread Out Bragg Peak CATANA: 62 Me. V proton beam

Depth dose measurements (protons) Spread Out Bragg Peak CATANA: 62 Me. V proton beam Measurements in PMMA Signal normalized at 12. 5 mm

IMRT Field 10 MV photon beam at Careggi Hospital Inserire mappa focus

IMRT Field 10 MV photon beam at Careggi Hospital Inserire mappa focus

Grazie per l’attenzione

Grazie per l’attenzione

Trasparenze di appoggio

Trasparenze di appoggio

TPR measurements (photons) For the same beam quality, detector centered at the isocentre, the

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. 6 MV photon beam at Careggi Hospital

Output factors (protons) Measurement performed at Catania

Output factors (protons) Measurement performed at Catania

Output factors (photon) Measurement performed at IBA site These good results have been obtained

Output factors (photon) Measurement performed at IBA site These good results have been obtained resolving packaging problems

Angular dependence Measurement performed at IBA site

Angular dependence Measurement performed at IBA site

Publications and dissemination • A patent has been deposited: Italian patent No. FI 2006

Publications and dissemination • A patent has been deposited: Italian patent No. FI 2006 A 000166, 30 June 2006, University of Florence, Inventors: M. Bruzzi, M. Bucciolini, D. Menichelli, C. Talamonti. International patent application No. PCT/IB 2007/001850 1. 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 Research. A, 552, (2005) 158 -162 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, 172109. 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 2 D dose measurements in radiotherapy”, Nuclear Instruments and Methods in Physics Research. A, 583, (2007) 109 -113 C. Talamonti, M. Bucciolini, M. Bruzzi, L. Marrazzo, D. Menichelli. : “Preliminary dosimetric characterization of a silicon segmented detector for 2 D dose verifications in radiotherapy“, Nuclear Instruments and Methods in Physics Research A , 583, ( 2007), pp. 109 -113. C. Talamonti, M. Bucciolini, M. Bruzzi, L. Marrazzo, D. Menichelli. : “Dosimetric characterization with 62 Me. V protons of a silicon segmented detector for 2 D dose verifications in radiotherapy , Nuclear Instruments and Methods in Physics Research A , 596 ( 2008), pp. 126 -130. 2. 3. 4. 5.

Sensitivity S is proportional to the active volume V and largely determined by the

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 t ( L = (Dt)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, 1261 -1267 Carrier lifetime decreases with dose due to the creation of generationrecombination centers. To mitigate the sensitivity decrease with the accumulated dose, commercially available Si diodes are usually pre-irradiated up to about 10 k. Gy 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.

Dose rate dependence (photons) 6 MV photon beam at Careggi Hospital The dose rate

Dose rate dependence (photons) 6 MV photon beam at Careggi Hospital 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). 60 Co source beam at Lucca Hospital Comparison of relative dose measured with the Si dosimeter and a Farmer ionization chamber.