First Results and Realization Status of a Proton Computed Radiography Device

Transcription

1 First Results and Realization Status of a Proton Computed Radiography Device V. Sipala for the PRIMA collaboration V.Sipalaa,b, D.LoPrestia,b, N.Randazzob, M.Bruzzid,e, D.Menichellie,d, C.Civininid, M.Bucciolinic,d, C.Talamontic,d, L.Marrazzoc,d, L.Capinerif, S.Valentinid,f G.Cuttoneg, G.A.P.Cirroneg, G.Candianog, E.Mazzagliag, a) Dipartimento di Fisica, Università degli Studi di Catania b) INFN, sezione di Catania c) Dipartimento di Fisiopatologia Clinica, Università degli Studi di Firenze d) INFN, sezione di Firenze e) Dipartimento di Energetica, Università degli Studi di Firenze f) Dipartimento di Elettronica e Telecomunicazioni, Università degli Studi di Firenze g) Laboratori Nazionali del Sud-INFN, Catania.

2 Outline Motivations of a Proton Computed Tomography Description of our Device First results obtained Conclusions 2

3 Proton Computed Tomography: why? Advantages of proton beam therapy: Maximum dose (Bragg peak effect) Finite range in tissue (protection of tissues) Main issues in the quality of treatment in proton therapy are: Patient positioning Dose planning 3

4 Proton Computed Tomography: why? Patient positioning: Currently performed using X-rays radiography in previous phase PCT allows better accuracy and single phase positioning / treatments Dose Calculation: Currently performed using X-rays computed tomography Problem: protons and photons have different interaction with matter PCT uses protons directly for dose calculation 4

5 Parameters of Proton Computed Radiography PARAMETER VALUE Proton beam energy MeV Proton beam rate protons/sec Spatial resolution < 1 mm Electronic density resolution < 1% Detector radiation hardness > 1000 Gy The critical parameter is the spatial resolution because of the multiple Coulomb scattering of protons 5

6 Reconstruction Principle: Most Likely Path L L A L C B A: Only entry position & direction known: straight line L B: Entry position & direction + exit position known: straight line L C: Entry position & direction + exit position & direction known: curved path L, banana-shaped, narrow confidence limits 6

7 Proton Computed Tomography concept Calorimeter Reveal the trace of the single proton using a silicon telescope Measure the residual energy of the proton using a calorimeter Silicon Telescope Silicon Telescope Reconstruct the most likely path of the single proton 7

8 Proton Computed Radiography Device 4 x-y TRACKER MODULES 1 CALORIMETER Entry and Exit position and direction Residual Energy 8

9 Single Tracker Module Digital Board Detector board 256 Microstrip detector DAC Vth 256 DigOut chip (x8) GEN FPGA control bus address bus Ethernet Unit data bus Trigger Trigger_en 9

10 Single Tracker Module Detector board with a detector and 8 chip containing the electronic front-end. Detector board Detector location Digital board 1 x-y plane consists of 2 single tracker module 10

11 Detector Description 53 mm x 53 mm n-type substrate with p-type implants 200 μm thickness 256 strips, each 57 μm thick 200 μm pitch Integrated resistance for bias 1.5MOhm DC PAD AC PAD Substrate bias PAD Guard ring Bias ring 11

12 Front-end chip Description 1.6 mm x 6 mm 32 channels P = 670 mw Vcc = +3.3 V Single channel OUT Charge Sensitive Amplifier Single strip Differentiator Integrator (high pass) (low pass) Comparator Buffer External threshold voltage 12

13 Calorimeter 4 YAG: Ce scintillating crystals Each crystal 30 x 30 mm2 x 100mm 4 Photodiode 18 mm x 18 mm YAG:Ce properties PHYSICAL PROPERTIES Density [g/cm3] 4.57 Hygroscopic No Chemical formula Y3Al5O12 LUMINESCENCE PROPERTIES Wavelength of max. emission [nm] 550 Decay constant [ns] 70 Photon yield at 300k [103 Ph/MeV]

14 Calorimeter readout U F bit D ig itizer/o s c illos c o p e Trigger Generator Board Electronic front-end AO 1-4 Σ V threshold Elettronic front-end DAC + Electronic front-end Electronic front-end Monostable Counter Trigger Tracker modules Trigger_en Event number 14

15 Detector characterization We tested 3 detectors. We performed the following measurements: Leakage current vs Bias Voltage Overall Capacitance vs Bias Voltage Inter-strip capacitance vs. Bias Voltage Comparison between curves measured at INFN (open circles) and by Hamamatsu (solid lines) 15

16 Electronic front-end characterization Detector board: First results 1 QIN=15000e Test of detector and front-end with Sr90 source 10mV e x p e rim e n t w it h n o is e w it h o u t n o is e V th (V ) V threshold (V) counts Width pulse (ns) Efficiency E f f ic ie n z a P ro to ty p e 2 8 VthUV d2 = 1.69V ig = V 600 V a n a = 3.3 V V th = V released charge (electrons) x x 10 5 Input charge (e-) 16

17 Calorimeter We tested a single crystal with a commercial electronic readout (low acquisition rate) at Laboratori Nazionali del Sud and Loma Linda Medical Center FHWM Resolution % 30 Measurements 1/E Good for high-energy Energy[MeV] Input energy beam vs resolution Center = 568,01 Width = 20,5 Resolution = 3,6% 0,8 0, ,4 0,2 0,0 200MeV Resolution about 1% 400 Counts normalized counts 1, channel Charge spectrum for 60 MeV proton beam Channels Charge spectrum for 200MeV IPRD08 SIENA 01 october

18 Conclusions A pct device is being built by the PRIMA collaboration Single tracker module Single parts exist as prototypes Detector board: complete Digital board: advanced development status Calorimeter YAG crystal: completely characterized Front-end electronics: prototype exists (commercial parts) Trigger generator: advanced development status Future plans (by the end of the year) Detector board: to be tested with proton beam (nov 08) Digital board: coupling tests with the detector board (dec 08) 4-crystals calorimeter: to be tested with 60MeV (oct 08) and 200MeV proton beam (nov 08) Calorimeter front-end electronics: new design (higher rate) Future plans (by the end of 2009) Complete device built

19 Thank you for your attention