Development of on line monitor detectors used for clinical routine in proton and ion therapy

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1 Development of on line monitor detectors used for clinical routine in proton and ion therapy A. Ansarinejad Torino, february 8 th, 2010

2 Overview Hadrontherapy CNAO Project Monitor system: Part1:preliminary Characterization tests and measurements.results Part2:Estimation of radiation effects.results.conclusions Future perspectives

3 GENERAL PRINCIPLE OF RADIATION THERAPY probability [%] Tumour control Complication rate dose [Gy]

4 Hadrontherapy photons Biological Effective Dose (%) protons Depth in Watter (cm) Depth dose distributions of Hadron beams

5 Spread Out Bragg Peak (SOBP) as composed of a number of Bragg peaks with different energies

6 Hadrotherapy Advantages: Low dose on surface High dose in depth (most energy at end of range) High precision on dose delivery (penetration depth is well defined and adjustable) dose to normal tissue minimised no dose beyond target Minimal lateral scattering and fragments effect

7 Centro Nazionale di Adroterapia Oncologica CNAO Particles and Energies: - Protons: Mev - Carbon ions: Mev/u Active system of dose distribution Beam dimension: 4-10mm(FWHM) Beam Intensity : - Max particles number/spill: 1010(p) 4 x 108 ( C+6) Three treatment rooms Extraction lines: -Three identical horizontal lines - One vertical line The CNAO Synchrotron Layout of the CNAO accelerators and beam transport lines

8 Active beam delivery system Active system of dose distribution Proton source Carbon source de/dz Synchrotron Scanning magnets Monitor system INFN and University of Torino in Collaboration of CNAO Foundation

9 On-line monitor system BEAM BOX1 Box1 BOX2 NOZZLE and MONITOR SYSTEM For each beam-line:5 parallel plate ionization chambers; 2 Integral chambers, 2 strip chambers, 1 pixel chamber In two completely indipendente boxes : BOX1, BOX2 (concerning read-out electronics and power supply)for safety reasons Gas used in chambers : nitrogen High voltage cathode polarization: + 400V

10 Monitor System Integral Chamber: Intensity Measurement Strip Chambers: Position Measurement Intensity Measurement Precision 100 µm Integral Chamber: Intensity Measurement Pixel Chamber: 2D Position Measurement 2D Intensity Measurement Precision 200 µm BOX 1 BOX 2

11 Preliminary Characterization Tests and Measurements Background Currents Reproducibility on a single point Uniformity of the sensitive area

12 Pedestals the leakage current in conditions of high voltage on and no beam Mean Counts/s at 400V Strip Chambers PixelChamber

13 Background Currents Pixel and Strip Chambers Mean Background current (fa) per channel Voltage (V) Strip X Strip Y Pixel Charge Quantum 200 fc For each voltage the measurement was repeated five times, every 60s Pixel chamber 157 fa Strip Y chamber 178 fa Strip X chamber 167 fa The typical therapy current ~10nA

14 Background Currents Integral Chambers Integral 1 200fC -208 fa Mean Background current per channel (fa) Voltage (V) The typical therapy current ~10nA 50 fc 200 fc 350 fc 2500 Integral 2 200fC fa Mean Background Current per channel (fa) Voltage (V) 50 fc 200 fc 350 fc

15 Detectors characterization X - ray Tests Data Acquisition System DAQ time =100 ms X Ray source with 2mm diameter collimator 50 kv and 160 mas BOX containing the ionization chambers Experimental Setup

16 REPRODUCIBILITY on a single point $ /,9, 3/ ;0,70, %037:381470, PC

17 Reproducibility Strip X/Integral 1 Strip Y/Integral 1 Ratio 1,3 1,29 1,28 1,27 1,26 1,25 1,24 1,23 1,22 1,21 1,2 1, Run Serie 1 Serie 2 Serie 3 Serie 4 Ratio Run Serie 1 Serie 2 Serie 3 Serie 4 StpX/Integral 1 0.4% StpY/Integral 1 0.7% Pixel/Integral 2 1.8% Ratio (Pxc/Int2) Pixel/Integral Run Serie 1 Serie 2 Serie 3 Serie 4

18 & # % Scan on 36 points (central area) 6x6 matrix Moving BOX 1A Moving the head of the X Ray Source

19 GAIN UNIFORMITY Total systematic error Statistical error Gain error ( σ ) 2 ( ) 2 ( ) 2 total = σ statf + σ gain RMS StripX StripY Integral 1 Integral 2 Pixel % σ total % σ statf % σ gain % 1.7% 2% 1.9% 1.7%

20 The radiation effects on the detectors and electronics of monitor system of CNAO facility The detectors of the monitor system and its electronic rack are placed in the Treatment room, then are typically working in a radioactive environment. The simulation of the radiation effects have been made to take account probably damage in electronics and to estimate its lifetime. Targets in the treatment room: NOZZEL :holding structure, BOX1 and BOX2, passive elements RACK : case, data acquisition system, power supply, gas panel

21 Nozzle Rack The beam-line in the treatment room : the position of NOZZLE and electronic rack

22 FLUKA cod. The simulation of distribution of secondary neutrons produced by 400 MeV/nucleon carbon ion beams The simulation of distribution of Secondary Neutron produced on the patient tissue ( the backward component) To qualify the radiation effects we simulate: Energy spectra Fluence Radiation dose rate

23 THE NEUTRON SECONDARY RADIATION PRODUCED ON THE PATIENT TISSUE: THE BACKWARD COMPONENT Energy spectra of the secondary neutrons produced in the backward direction on the patient tissue (FLUKA simulation).primary beam: 400 MeV/u carbon ions.

24 The energy distribution of the secondary neutrons produced in the backward direction in comparison with the total energy spectra of the secondary neutrons

25 NOZZLE Approssimazione NOZZLE a parallelepipedo con struttura in Al e interno di aria RACK X Approssimazione ARMADIO a parallelepipedo di ferro omogeneo The fluence rate of the secondary neutrons during the treatment with 400 MeV/c carbon ions at the higher intensity Z

26 0 z 1

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29 Expected Dose To evaluate the expected dose delivered to the targets during a therapeutic treatment, there are the following assumptions: - considering 52 working weeks in a year; - Working days are 6 weekly; - working hours are 12 daily; - treatment time in an hour is 3 min; The NOZZLE A typical standard radiotherapy treatment delivers about 5 x 10 4 (n x cm -2 ) /s on the nozzle Thus the NOZZLE should be exposed to a integrated neutron fluence: 3.4 x n/cm 2 yearly The RACK A typical standard radiotherapy treatment delivers 5x10 2 (n x cm -2 ) /s on the rack Thus the RACK should be exposed to a integrated neutron fluence: 3.4 x 10 8 n/cm 2 yearly

30 Conclusions Comparison with experimental results Radiation damage studies of a recycling integrator VLSI chip - The electrical characteristics of the chip change by less than 1% for a total integrated fluence of 4x10 12 neutrons. - No Single Event Upsets were observed up to a fluence of neutrons. Refers to LHC radiation damage experiments; - CMOS technology is less sensitive to neutron: n/cm 2 - Non CMOS technology (bipolars) sensitive to neutron: n/cm 2

31 FUTURE PERSPECTIVES Characterization tests with Microfocus X-ray generator Characterization tests at CNAO