Design and development of a Si segmented detector for 2D dose measurements in radiotherapy

Transcript

1 Design and development of a Si segmented detector for 2D dose measurements in radiotherapy D. Menichelli, M. Bruzzi, M. Bucciolini, M. Casati, A. De Sio, L. Marrazzo, C. Talamonti: INFN and University of Florence M. Brianzi: INFN Florence C. Piemonte, A. Pozza, N. Zorzi: ITC-IRST Trento M. Tesi: CNR-IFAC Florence

2 Conformal Radiotherapy With modern diagnostic modalities (CT, MR and PET), precise tumor localization is possible, permitting to obtain irradiation conformal to the target......by means of: a) many gates with beams focalized toward the isocenter; b) MLC collimators to shape the beam cross section.

3 Instruments for Dose Verification of Treatment Plane Accurate determination of the 2D absorbed dose distribution requires detectors with: a) high spatial resolution; b) response independent of the dose rate and energy; fast and stable in time; c) good linearity and wide dynamic range Array alternative to films: PTW 2D-array 729 ionization chambers 27x27 cm 2 Pitch 10 mm Sun Nuclear mapcheck 445 silicon diodes 22x22 cm 2 pitch: 1.0 cm Scanditronix-Wellhofer Matrixx 1024 cylindrical ionization chambers 24 x 24 cm 2 Pitch 7.5mm

4 Introduzione: rivelatori al silicio Within the European project MAESTRO (Methods and Advanced Equipment for Simulation and Treatment in Radio- Oncology), we are developing a modular 2D Si monolithic detector (the first monolithic silicon sensor for dosimetry manufactured ever). Attractives of Si: a) linear relationship between photon energy and e/h pairs; b) high sensitivity (Si ~3.6 ev/pair) small active volume high spatial resolution; c) well developed technology for the production of segmented monolitic planar detectors.

5 Specifications: a) Spatial resolution: ~1 mm granularity b) Active area: at least 20x20 cm 2 c) Low Background signal: < 0.1% of signal (zero bias operation needed) Response speed and signal strength are of no concern 9-modules design: A single module cut from each wafer. Nine modules will be used to cover an area of about cm 2. System complexity: ~4k channels

6 Design and production of silicon modules 441 Si n+p diodes 50 µm epi layer growth on MCz p. Active area: 6.29x6.29 cm 2. Segmentation: 21x21 pixel (2 2 mm 2, 3 mm pitch). Overmetal strips to 441 pads along one single side. Diffused guardring structure at 20 µm from pads. DC coupling.

7 Test Strumentazione: under probe station: il sensore average zero-bias generation/recombination current : i 0 =13±7 pa Temperature coeff.: di 0 /dt=4 pa/ C. Italian patent No. FI2006A000166

8 441 Strumentazione: ch Prototype - final lettura, assembling acquisizione e analisi Readout electronics: current integration mode (Op. amp. LMC6084, C=1.00±5% nf); Multiplexing 8:1; T=0.1-4 s; Acquisition: A/D NI 6071E (12 bit, 64 ch., f max =1.25 MHz). In last prototype pitch adapter and 250 µm pitch PCB are replaced by a cost effective high density 100 µm pitch PCB, improving SNR. R (cgy/min) Sensitivity (nc/cgy) q 0 (pc) Dark σ 0 (pc) SNR Repeatibility σ% (%) N 0.5 (%) σ% (%) Reproducibility σ'% (%) N 1 (%)

9 441ch TERA-based prototype

10 Device Silicon Module (15 6x6 samples from IRST) Milestones State manufactured and tested Completed /to be completed by: Aug ch prototype with discrete electronics Assembled and tested March 2006 ASIC choice and testing Done June ch prototype with integrated electronics Design manufacturing Assembling Debug X Done Done Done To be done Sept Jan May 2007 May 2007 Beam test X To be done Sept Full detector 4k ch Design manufacturing X OX Done, in part In progress, in part during 2008 Assembling X To be done Debug X To be done Beam Test X To be done

11 Design of TERA-based 441ch system Each module: 7 TERA06 dies bonded on a high density 100 µm pitch PCB

12 Proton Imaging INFN: sezioni di Firenze, Catania e LNS Università di Firenze: Dip. di Energetica, Elettronica e Telecomunicazioni, Fisiopatologia Clinica. Università di Catania: Dip. di Fisica. Finanziato da INFN (esperimento PRIMA) e MIUR (PRIN 2006),

13 Spatial accuracy of proton therapy is presently limited by the uncertainty of stopping power distribution (calculated from X-ray tomography). stopping power YAP(Ce) p 240MeV Goal: to develop a pt apparatus to measure directly stopping power maps of tissues. Main problem: multiple Coulomb scattering. THUS It is necessary to characterize the trajectory of each proton in term of entrance and exit angle, entrance and exit position and residual energy.

14 Prime Simulazioni MLP The most likely path of an energetic charged particle through a uniform medium D C Williams Phys. Med. Biol. 49 (2004) La misura degli angoli in entrata e uscita agiscono da condizioni al contorno per il calcolo di MLP 200 MeV Protons, 20 cm water, most likely, 1 σ and 2 σ path

15 Proton Trasmission Radiography: Il Principio Il dispositivo si basa sull idea di misurare singolarmente sia l energia che la direzione di ogni protone incidente.

16 Attività di ricerca preliminare svolta in MOPI Collaborazione: INFN Firenze Catania LNS SCIPP UCSC e Loma Linda Univ. Medical Center Test Beam LLUMC - Maggio 2005 I telescopi misurano la posizione del protone in entrata ed uscita su un area di 4cm x 4cm. Il calorimetro (5cmx5cm) misura l energia in uscita. calorimetro Un modulo mobile tra gli assorbitori misura lo spostamento 2-D del fascio in diverse posizioni nell assorbitore segmentato tessuto equivalente (12 lastre PMMA di spessore 1.25cm ) z (mm)

17 Set-up del sistema

18 Programma del progetto 1. PTR A) Telescopio al Si per la determinazione delle posizioni e degli angoli di entrata ed uscita. Piani mobili inseriti in materiale tessuto equivalente segmentato per la determinazione del cammino più probabile dei protoni nel mezzo. B) Calorimetro per la misura dell energia del protone. C) Ricostruzione del cammino più probabile del protone nel mezzo Fascio protoni Piani di materiale tessuto equivalente Calorimetro Telescopio in entrata Moduli mobili Telescopio in uscita

19 Proton Beam Tracker digital Board Front End board Ethernet Unit RAM FPGA 8 DAC Latches 256 Test Vth ASIC (x8) 256 DO Microstrip sensor Trigger 8 GEN Enable Ethernet switch Tracker x-y plane no. 1 tracker module... x-y plane no. 5 Trigger enable Bus Digital Analog AO1-4 Σ + - Notebook threshold 8 Enable PCI/PCMCIA bridge Oscilloscope Board Ch0-3 Trigger Calorimeter AO1 AO2 AO3 AO4 Trigger generator Enable Scintillator Photodiode Preamplifier Shaper 8 Trigger Monostable Counter 8 GEN Calorimeter digital Board Trigger

20 Lavoro di tesi Per entrambe le attività: -progetto e sviluppo di elettronica analogica e/o digitale -software di acquisizione -caratterizzazione e assemblaggio sensori -debug e messa a punto del sistema di misura -test sotto fascio -analisi dati