Readout Electronics for a Proton Tomography Apparatus

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Readout Electronics for a Proton Computed

Tomography Apparatus

D. Menichelli

1,2

_{, M. Brianzi}

2

_{, L. Capineri}

3

_{, C. Civinini}

2

_{, A. Fucile}

5

_,

D. Lo Presti

4,5

_{, N. Randazzo}

5

_{, M. Russo}

4,5

_{, V. Sipala}

5

_{, M. Tesi}

6

_,

S. Valentini

3

1. Dipartimento di Fisiopatologia Clinica, Università di Firenze 2. Sezione di Firenze, INFN

3. Dipartimento di Elettronica e Telecomunicazioni, Università di Firenze 4. Dipatimento di Fisica, Università di Catania

5. Sezione di Catania, INFN, Catania

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MOTIVATIONS FOR pCT

Stopping powers are the main parameters for dose calculation in proton radiotherapy. They are derived from measured attenuation coefficients µ of conventional xCT.

The error intrinsic in this conversion (due to µ(η_e,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]

Main aim of pCT: direct measurement of stopping power...

...and, possibly:

a. Lower dose to the patient, with respect to xCT (according to MC simulations). b. Increase of low-contrast resolution

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MAIN DIFFICULTY WITH pCT: multiple Coulomb scattering

200 MeV Protons, 20 cm water Most Likely, 1σ and 2σ path

D C Williams Phys. Med. Biol. 49 (2004) 2899–2911

To obtain high space and energy accuracy:

1. determination of protons Most Likely Path (MLP)

2. single proton tracking

Entrance and exit angles and positions are

boundary conditions for MLP calculation.

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BACKGROUND

Initial studies with a Si single-sided strip telescope by UCSC and LLUMC. Use of Si detectors (194 µm pitch, 400 µm thickness) to measure:

a) protons trajectory;

b) energy loss, from time over threshold (TOT).

Limits:

1) slow acquisiton rate (1kHz).

2) Low energy resolution (25% at 250 MeV), improved in a later prototype by a separate calorimeter.

H. F. -W. Sadrozinsk et al., NIM A 514 (2003) 215–223.

M. Bruzzi et al. , IEEE Trans. Nucl. Sci., 54 (2007) 140 - 145.

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COLLABORATION AIMS

1) realize a high-performance prototype for proton radiography

2) validate the prototype with pre-clinical studies

3) conceive a configuration for a pCT system. e.g.: comparison of predicted MLP with tracking measurements > 1000 Gy Radiation hardness < 1% electron density resolution < 1 mm Space resolution ~106 _1/sec Proton rate 250-270 MeV Proton Energy

Research supported by:

INFN (Natl. Inst. of Nucl. Phys.), "PRIMA" experiment

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Notebook PCI/PCMCIA bridge Ethe rnet s w itch

x-y plane no. 1

“Oscilloscope ” Boa rd Scintillator Photodiode Preamplifier Shaper

Calorimeter digital Board Trigger generator Counter C h0-3 T rigge r 8 Cal o rimet e r GEN Digital Analog Bus 8 Enab le Trigger x-y plane no. 5

. . . Tra c ker tracker module Proton Beam T rigge r_en

AO1 AO2 AO3 AO4

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Trigger

Microstrip sensor

Front End board

256 ₂₅₆ DAC 8+2 GEN 8 S-RAM (4) 1MBx16 Ethernet U nit ASIC ( x 8)

Tracker digital Board

Test Vth Trigger_en DO 2

TRACKER MODULE

control bus address bus data bus FPGA

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Si SENSOR

53x53 mm2

p+-on-n strips

256 ch, 200 µm pitch 200 µm thickness tradoff between energy loss and

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Sensor Depletion Voltage (from C-V) 0 2 4 6 8 10 12 50 55 60 65 70 75 80 85 90 Altro Depletion Voltage [V] E n tr ies/ b in

Si SENSOR PERFORMANCES

V_fd<75 V i(100V)<1 µA i(200V)<3 µA C= 54pF/cm (coupling) C= 1.5 pF/cm (interstrip)

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ASIC design

6.6 x 1.6 mm2 32 inputs - 32 outputs 670 mW power consumption Vcc=+3.3 V Charge Sensitive Amplifier Differentiator (high pass) I Integrator (low pass) II Integrator (low pass) Comparator Buffer External threshold voltage OUT Single strip Single channel

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Rise time = 12ns @ CL = 30pF Fall time = 13ns @ CL = 30pF Width ~ [250 + 0.50×E(keV)] ns Dynamic range ~ 3 MeV

ASIC CAD SIMULATION: output signal

Ein=200 keV Vth=50 mV

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Front end board ASICs

Routing strips Microstrip detector Connector

Tracker digital board Digital electronics FPGA S-RAM blocks Ethernet unit Other I/O

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Calorimeter

5 10 15 20 25 30 FHWM Resolution % Measurements 1/E

Charge spectra for 62 MeV proton beam

0 200 400 600 800 1000 1200 0,0 0,2 0,4 0,6 0,8 1,0 Center = 568,01 Width = 20,5 Resolution = 3,6% normalized counts channel 20 25 30 35 40 45 50 55 60 65 100 200 300 400 500 600 channel Measurements Linear Fit of Data1_B Linearity = 0,85%

YAG:Ce

YAG:Cepropertiesproperties

40-50

Photon yield at 300k [103_Ph/MeV]

70 Decay constant [ns]

550 Wavelength of max. emission [nm] Luminescence properties Y3Al5O12 Chemical formula No Hygroscopic 4.57 Density [g/cm3_] Physical properties

The relationship between the input energy

beam and the peak position The relationship between the input energy_{beam and the resolution}

Good for high-energy

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Photodiode

Charge Sensitive Amplifier CREMAT CR110 Calorimeter front-end Shaper CREMAT CR200 YAP:Ce Crystal

Final calorimeter layout to be realized in 2007

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+ -Σ 8 Trigger_en Vth' Trigger Monostable AO 1-4 Trigger Generator Calorimeter front-end Calorimeter front-end Calorimeter front-end Calorimeter front-end UF2-4000 14 bit Digitizer/Oscilloscope Tracker modules

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Purchased

Development

DAC board

Preliminary versions available during Nov. 2007.

Development FPGA Software DAC board Purchased Crystals Calorimeter Development Communication Commissioning: Sept. 2007 Production: Oct. 2007 Test & debug: Nov. 2007

Design

Production Test & debug

Digital board

Purchased

Readout lectronics

Delivery: Oct. 2007 Test & debug: Nov. 2007

Design

Production Test & debug

Digital board

Delivery: Sept. 2007 Bonding: Oct. 2007 Test & debug: Nov. 2007

Design Production

Bonding Test & debug

Front end board

Delivery: Sept. 2007. Test & debug: Sept. 2007.

Design Production Test ASIC Detector Design Production Test (IV, CV) Tracker (1st module) Assembling of 1st tracker module: dec. 2007 Test with calorimeter: during 2008. Assembling of the full telescope: dec. 2008

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CONCLUSIONS

The construction of a pCT system has been approached

A telescope has been designed: a. SSD Si tracker;

b. YAG:Ce segmented calorimeter.

Electronics characteristics: a. 1 MHz event rate.

b. 32 ch readout ASICs designed within the collaboration; c. control and data acquisition by FPGA circuits;

d. trigger generation from calorimeter data;

e. pre-triggered calorimeter waveforms acquisition (precise energy loss meas.) f. possible energy loss in silicon measured by TOT.

Milestones

a. Dec. 2007: assembling of first tracker module.

b. Dec. 2008: assembling and test of the full telescope. c. Dec. 2008: design of the pCT system.