Dosimetry at accelerators: state-of-the-art and applications to … Colloquia... · 2019. 5....
Transcript of Dosimetry at accelerators: state-of-the-art and applications to … Colloquia... · 2019. 5....
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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• 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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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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Stray Rad Monitors
Area Radiation Monitoring
Ventilation Monitors
Water Monitors
ARCONVME Chassis
Area Monitoring (ARCON)
RA
MS
ES
Induced Activity
Monitors
GRAMS
Radiation & Environmental Protection at CERN
Courtesy Hamza Boukabache, CERN
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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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supervisionUninterruptible 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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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 2020source: 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
DatabaseREMUS 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
PSKindergarten
• 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 requirementLow power optimization is one of the main challenges. The devices shall be:
• Portable, small and compact
• Battery powered
• Battery lifetime of several years
Cu
rre
nt (m
A)
Optical
Data transfer
From the standard D-shuttle with optical data extraction to the new long range wireless D-shuttle with SPI
Time (s)C
urr
en
t (m
A)
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 sideEutectic 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
+
AmplifierComparator
000001
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
Bia
s V
olta
ge
Co
mm
on
ba
ck-s
ide
ele
ctr
ode
Pix
ela
ted
fro
nt-
sid
e
ele
ctr
od
e
Pixel electronics
Thresholdlevel
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
AmplifierComparator
000088
Pixel electronics
Thresholdlevel
Clk Counter:10-80MHz
AmplifierComparator
0000383
Pixel electronics
Thresholdlevel
t
Close shutter
t
Counter value ~ Arrival time
Direct measurement of particle energy or its arrival time in each pixel
Court
esy Z
. V
ykydal, I
EA
P P
rague
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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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Trip
le G
EM
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
The Gempix - An Ultra Pixellated Gas Detector
• The Gempix combines two CERN developed
technologies, GEM detectors and the Timepix to
produce a gas detector with 55 um readout granularity
(c)
(1) Gas Supply
(2) High Voltage
(3) Entrance Window
(4) GEM Foils
(5) FITPix Readout
Sensitive area = 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-onGas 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