Dosimetry at accelerators: state-of-the-art and applications to - - PowerPoint PPT Presentation

Dosimetry at accelerators: state-of-the-art and applications to medicine

University of Milano, 10th May 2019 Marco Silari CERN, Geneva, Switzerland

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• M. Silari - Dosimetry at accelerators - UNIMI, 10 May 2019
• Radiation & Environmental Protection at CERN: past, present and future
• The W-MON project
• The Medipix/Timepix hybrid pixel detector
• MARS CT
• The GEMPix and its application in hadrontherapy

Outlook of the presentation

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• M. Silari - Dosimetry at accelerators - UNIMI, 10 May 2019

Radiation & Environmental Protection at CERN

REMUS: CERN Radiation and Environment Monitoring Unified Supervision

PS

In 2019: 3211 Measurement channels: 864 RP main channels + 1824 auxiliary 523 Environmental channels 26 Types (categories) of monitoring stations 365 days/year, 24/7 operation

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• M. Silari - Dosimetry at accelerators - UNIMI, 10 May 2019

Stray Rad Monitors Area Radiation Monitoring Ventilation Monitors Water Monitors ARCON VME Chassis Area Monitoring (ARCON)

RAMSES

Induced Activity Monitors GRAMS

Radiation & Environmental Protection at CERN

Courtesy Hamza Boukabache, CERN

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• M. Silari - Dosimetry at accelerators - UNIMI, 10 May 2019

Radiation & Environmental Protection at CERN

REM counters

Gas filled, high pressure ionization chambers

Beam-on: to protect workers in areas adjacent to accelerator tunnels and experiments against prompt radiation (mainly neutrons, E < some GeV) Alarm function

Air filled ionization chambers

Beam-off: to protect workers during maintenance and repair against radiation fields caused by decay of radionuclides (mainly gammas, E < 2.7 MeV) No alarm function

Site Gate Monitors

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supervision Uninterruptible Power supply Alarm Unit

Worker

Access System / Machines Radiation Monitor

High Reliability components –

Military, Automotive or Industrial qualification

Redundant Electronic Embedded Testability

Courtesy Hamza Boukabache, CERN

CROME (CERN RadiatiOn Monitoring Electronics)

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CROME Rackable System

Courtesy Hamza Boukabache, CERN

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W-MON: remote control of radioactivity in waste containers

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• M. Silari - Dosimetry at accelerators - UNIMI, 10 May 2019

Meyrin Prévessin

Origin of the waste containers:

• France: Prévessin site, all SPS and LHC site except BA5, BA6, and LHC P1
• Switzerland: Meyrin site, SPS BA5, BA6 and LHC P1

Number of household waste containers controlled:

• France:  100
• Switzerland:  150

Manual control procedure:

• France: once per week, control duration 2 hours
• Switzerland: three times per week, control duration 2 hours

2017 report:

• 991 measurements campaigns
• 104 problems (weather conditions, accessibility, background too high,…)
• 36 positive controls

Current waste control procedure

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7 billion devices connected in 2018 15% increase from 2017 10 billions by 2020

source: IoT Analytics

Main applications:

• Business/manufacturing 40.2%
• Health care 30.3%
• Retail 8.3%
• Security 7.7%
• Transportation 4.1%

source: Gartner, Inc

Internet Of Things

The IoT solution

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CERN

Distributed network of radiation sensors to monitor radioactivity in waste End-devices Gateway / Concentrator Server Database REMUS User apps

The W-MON project

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• 1. Gamma rays radiation detection
• 2. Sensitivity down to background level
• 3. Robust device, resistant to adverse weather conditions, temperature variations, mechanical

shocks

• 4. Low power consumption (battery powered)  minimum maintenance
• 5. Wireless data transmission
• 6. Real-time information
• 7. Relevant information: alarm for radiation level above threshold, alarm for equipment

malfunctioning, GPS information, data logging

Requirements for an automated system

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The W-MON project

• 2014: Identification of the sensor technology

Proof of principle  D-shuttle optimal solution as radiation sensor

• 2015: CERN collaboration agreement with Chiyoda and AIST

Feasibility studies  Determination of the number and position of the sensors in the container

• 2016: Data handling and communication  The beginning of LoRaWAN at CERN

Collaboration with IT for the deployment of a distributed network of LoRa gateways at CERN

• 2017: Reliability tests

Development of a wireless version of the D-shuttle Development of a custom server and data base before integration into REMUS

• 2018: Migration to CERN LoRa network

Design of the final customized wireless radiation solution (sensor + communication boards) Optimisation of power consumption

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Current approach: D-shuttle

D-shuttle personal dosimeter Reader Reader + PC interface

• Hamamatsu Si PIN diode
• Communication board with optical and 2.4 GHz RF transmitters
• Shock sensor
• Lithium battery, lifetime 1 year (2 readings per day)
• Dose reading from 0.1 µSv to 100 mSv
• Size 68 mm x 32 mm x 14 mm and 23 g weight

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Low bit rate -> Low consumption / Frequency band 868 MHz (EU), (920-925 MHz Japan)

Devices Gateway 4G/3G/WiFi Ethernet LoRA Up to 15 km range LoRaWAN protocol Network server 4G/3G/WiFi Ethernet

LoRaWAN: Long Range Wide Area Network

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Test in operational conditions (April – November 2017)

Industrial radiography in a nearby building

Lid Middle Bottom

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LoRa @ CERN

Gateway position Points received nTOF ISR PS Kindergarten

• Five devices registered and sending data to the CERN LoRa network
• LoRa range tests and antenna deployment in collaboration with CERN-IT group
• Full coverage of all CERN sites by 2019

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The low power consumption requirement

Low power optimization is one of the main challenges. The devices shall be:

• Portable, small and compact
• Battery powered
• Battery lifetime of several years

Current (mA)

Optical Data transfer

From the standard D-shuttle with optical data extraction to the new long range wireless D-shuttle with SPI

Time (s) Current (mA)

New transmission time with SPI = 175 ms !! 0.12 mAh 0.023 mAh with SPI LTC battery with nominal capacity of 2.5 Ah

60 65 70 75 80 85 90 60 65 70 75 80 85 90

Time (s)

Integrated current

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Master - slaves All masters

WiFi

master

1) The master waits for the data from the

• slaves. Data is sent via WiFi

2) Master sends all data through LoRa to the server

master

1) Each master extracts its own data from the dosimeter 2) Each master sends its own data to the server via LoRa

Possible W-MON architectures

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Exploring other options

• Another candidate – BG51 gamma radiation sensor from Teviso
• Ultra low power requirement (25 µA)
• Detector sensitivity: 5 cpm/µSv/h
• High immunity to RF and electrostatic fields
• Measurement range of dose rate 0.1 µSv/h to 100 mSv/h
• Pulse count rate: 5 cpm ± 15% for 1 µSv/h radiation dose rate

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Medipix/Timepix and some medical applications

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Hybrid pixel detectors

• Hybrid pixel detectors are used in high energy physics (HEP) experiments

because they provide practically noise-free ‘images’ of particle collisions taken with the equivalent of a very high speed shutter

• A preamplifier amplifies the charge deposited by a passing particle in a sensor

producing a fast shaped pulse

• This pulse is compared with a threshold
• Given the very small capacitance at the input of the pixel electronics, the front-end

provides a response with an equivalent input noise charge of 100 e− rms even at shaping times of 25 ns. If a threshold is set at 1000 e− the binary information contains practically no noise

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Schematic of a hybrid pixel detector with the sensor chip and the electronics chip connected via bump bonds

• In the hybrid pixel detector architecture the radiation sensor element and the readout are

processed separately

• The sensor is segmented with the same geometry as the readout chip and detector and

readout cells are connected using standard flip-chip technology

• The separation in processing allows for independent optimization of readout and sensor

and different sensor materials can be used with the same readout.

Hybrid pixel detectors

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Medipix2/Timepix assemblies

Single assembly Pixels: 256 x 256 Pixel size: 55 x 55 mm2 Area: 1.5 x 1.5 cm2 Quad assembly Pixels: 512 x 512 Pixel size: 55 x 55 mm2 Area: 3 x 3 cm2

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Bump bonding

• Hybrid pixel detectors use flip chip technology to connect the pixel readout chip to the sensor material
• The individual bump bonds between a sensor and a readout pixel is 25 µm in diameter and made of

Pb-Sn solder (for 300 μm and 700 μm Si assemblies) or sometimes indium (for 1 mm thick CdTe sensor)

SEM images before assembling The Si sensor side Eutectic tin-lead solder bumps sitting on top of the Medipix2

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Timepix

• Readout chip fully compatible with Medipix2

electronics/software

• 4 operational modes
• Counting (= Medipix2 single threshold mode)
• Time over threshold mode (~ energy deposited)
• Arrival time mode
• Single hit
• Mode can be set in each pixel independently, allowing

for concurrent energy and arrival time measurements

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N+ P+ Si

Counter:

Particle count

+

Amplifier Compa rator

000 001 Planar pixellated detector bump-bonded to read-out chip Ionizing particle creates a charge in a sensitive volume The charge in each pixel is amplified and compared with a threshold Digital counter is incremented

Bias Voltage

Common back-side electrode Pixelated front-side electrode

Pixel electronics

Threshold level

Courtesy Z. Vykydal, IEAP Prague

Principle of single particle counting detector

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Timepix

Time-over-Threshold: ToT Arrival Time: TimePix

The Ref_clock is used to generate the clock Counter value ~ Energy

Clk Counter:

10-80MHz Amplifier Compa rator

000 088

Pixel electronics

Threshold level

Clk Counter: 10-80MHz

Amplifier Compa rator

000 0383

Pixel electronics

Threshold level t

Close shutter

t

Counter value ~ Arrival time

Direct measurement of particle energy or its arrival time in each pixel

Courtesy Z. Vykydal, IEAP Prague

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Handles plug-in mgmt and mediate access to the MPX Control Library Handles several MPX devices connected to PC Stepper motor control unit Revolver for beam hardening corrections Interface HW control Setting MPX parameters, acquisition ctrl, TH equalization, DAC control panel, cluster analysis,…

Data acquisition: the Pixelman software package

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Pattern recognition of tracks

a) 241Am alpha source gives clusters of ~5x5 pixels. The cluster sizes depend on particle energy and threshold (discriminator) setting b) Signature of X-rays from a 55Fe X-ray source. Photons yield single pixel hits or hits on 2 adjacent pixels due to charge sharing c) 90Sr beta source produces curved tracks

Medipix with 300 μm thick Si sensor

Tracks of particles in solid-state silicon are visualized online in a similar way as in nuclear emulsions, cloud chambers or bubble chambers

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(e.g., protons and neutrons >1 MeV)

Cluster analysis

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X-ray imaging

Images taken with an equalized Medipix2 quad: Left: 500 ms acquisition of an anchovy with a W X-ray tube at 15 kVp Right: 100 ms acquisition of a wrist watch with a W X-ray tube at 50 kVp

• Medipix3RX detector chip bonded to Si sensors at 110 µm pitch

with 8 energy bins per pixel and 2 ms frame readout

• 360, 720 or 1440 frames, Al or Brass filters
• 120 kVp, 350 μA x-ray source with helical scan mode
• Precision horizontal in vivo sample stage with gas lines, monitoring

inputs and temperature sensors

• Iterative reconstruction and processing algorithms quantify the

concentration of elements and compounds in mg/mL

• Visualization workstation with HP Zvr 3D virtual reality display for

image analysis

Colour coded material identification

Pre-clinical spectral scanner

Courtesy Pierre Carbonez, CERN

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MARS CT scanner

First organ dose measurements on mice with the MARS-CT scanner using TLDs placed in plastic bags inserted in a mouse

Courtesy Pierre Carbonez, CERN

MARS CT scanner

Courtesy Pierre Carbonez, CERN

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Human MARS CT scanner

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GEMPix and some medical applications

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70 µm 140 µm

Gas Electron Multiplier:

• 50 mm thick kapton foil
• 5 mm of copper on each side
• high surface-density of bi-conical channels

The three functions

• Conversion
• Amplification
• Readout

are well separated

High level of particle discrimination by adjusting the gain of the individual GEM foils - Total gain max 105

Triple-GEM (Gas Electron Multiplier)

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Triple GEM Readout Electronics

The GEMPix - An Ultra Pixelated Gas Detector

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The GEMPix combines two CERN technologies: GEM detectors and the Timepix to produce a gas detector with 55 µm readout granularity (1) Gas Supply (2) High Voltage (3) Entrance Window (4) GEM Foils (5) FITPix Readout

Sensitive volume = 3 x 3 x 1.2 cm3

• Marie Curie Initial Training Network funded by the European

Commission 7th Framework Programme, Grant Agreement 289198, 2012-2016

The GEMPix - An Ultra Pixelated Gas Detector

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GEMPix final assembly

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4 naked Timepix ASICs with 512 x 512 pixels, 55 µm x 55 µm pixel size Different readout modes possible:

• Pulse counting
• Time of Arrival (ToA)
• Time over Threshold (ToT) -> deposited energy

Timepix: frame based signal digitization

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X-ray detection: 5.9 keV photons from 55Fe source

Ar F e

20% energy resolution for 5.9 keV

Timepix: frame based signal digitization

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The detector is a naked quad Timepix : The active area is 8 cm2 The particle track is analysed with 512 pixels in  3 cm length This is equivalent to 30 µm of tissue … with 17 samples/µm

Head-on Side-on

Gas flux AR CO2 Triple GEM Mylar window

Particles to be analysed

Gas flux Triple GEM

Particles to be analysed

Length analysed

GEMPix: two operating modes

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Bragg Peak Beam

Tumou r

An integrated system for measurements of 3D energy deposition in water by clinical ion beams

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• S. Giordanengo et al. (2017): ‘Review of technologies and procedures of clinical dosimetry for scanned ion beam radiotherapy’
• Hadron therapy: well-defined region of energy deposition (Bragg curve with Bragg peak)
• QA: beam QA (range, spread out Bragg peak, …), typical dose uncertainties: order of 1%
• Patient treatment plan verification: typically arrays of ion chambers with little spatial resolution
• GEMPix provides superior spatial resolution

Quality Assurance in hadron therapy

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• Water phantom donated from Luzern hospital equipped with GEMPix, reference PTW ion

chamber + readout

• Ion chamber, GEMPix and movement in water phantom integrated in one system (HW/SW)

IC Beam

Measurements at CNAO – Italian National Centre for Oncological Hadron therapy

GEMPix integrated in water phantom

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280 MeV/A carbon ions, 0.01 s frame, ASIC in particle counting (Medipix) mode, 105 ions in frame

Pixels allow for high count rates - beam monitoring

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• Beam spot taken on Plateau, Bragg Peak and Tail
• Beam halo: single particle reconstruction
• 2D images with much better spatial resolution than with an ion chamber

Measurements with 12C ion beam at CNAO

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After corrections: most data points within ± 10% compared to FLUKA simulation

12C ion beam, 150 mm range: corrected Bragg curve

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Beam Bragg Peak Fragmentation Tail

3D dose reconstruction after depth scan

Plateau

3D energy deposition by 12C ion beam

Thank you for your attention