Carbon nanotube field emission
based imaging and irradiation
technology development
for cancer research and treatment
Sha Chang1 and Otto Zhou2
Dept. of Radiation Oncology1 and Physics & Astronomy2
University of North Carolina Medical School
Outline
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Carbon nanotube field emission technology
CNT-based imaging systems (available)
„
Micro-CT
„ Mammography tomosynthesis
„ Gantry-mount IGRT
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CNT-based irradiation systems
(development update)
„
Single cell irradiation
„ Micro-RT (irregular field and IMRT)
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Future directions
Carbon nanotube (CNT) & field emission
(1-50nm in diameter, ~1-10μm long tube)
CNT
eeeeeee-
Electric field (not heat)
controlled electron emission.
Basic structure of CNT cathode
Gate electrode
e- e- e- eInsulator
Variable voltage
power source
Substrate
Carbon nanotube film
Ultra-high current: 2000 A (8cm source)
Today’s X-ray technology
-
Siemens direct cooling tube
>100 year old technology
High operating temperature
Large size
Rotating anode tube
Slow response time
Limited resolution
Single pixel
Key advantages of CNT x-ray technology
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High temporal resolution
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Multi-pixel source array
Schematic of the prototype CNT field
emission multi-pixel microbeam array.
Small animal research technology
Challenges:
• improve temporal resolution,
• better physiological gating,
• faster scanning time,
• lower dose,
•better contrast
Human
Rat
Mouse
weight
(grams)
70,000
250
25
breaths
/minute
12
85
120
heartbeats
/ minute
60
300
600
CNT Micro-Focus Field Emission X-Ray Source
for in-vivo imaging of small animal cancer models
50-100um resolution, 0-50kVp, 1-3mA tube current, 10-100ms pulse width
CNT field emission imaging technologies
Single source micro-CT
Cyclops 1.0
Charybdis 1.0
J. Zhang et al (2005)
UNC dynamic micro-CT scanner
Charybdis 1.0
J. Liu et al./Zhou Lab/ Appl. Phys. Lett. 2006; G. Cao et al, SPIE Medical Imaging 2008
Respiratory gated μCT imaging
(free-breathing anesthetized mice)
(a)
(b)
(c)
(d)
Expiration
-12lp/mm at 10% MTF
--50ms temporal resolution
peak
(0.48ml)
Inspiration
base
(0.53ml)
G. Cao et al. SPIE Medical Imaging 2008; G. Cao et al. Phys Med Biol 2009
Cardiac gated μCT imaging
Reconstructed slice images show clear difference between
systole (a) and (c), and diastole (b) and (d) in the axial and
coronal views of a mouse heart, respectively
Detection of Vascular Calcification
Proximal aortic arch
CNT FE multi-pixel x-ray imaging
Source Array
Stationary
Tomosynthesis
Micro-RT
Single Cell
Irradiation
Subject
IGRT
Detector
Sha_chang@med.unc.edu
Detector
Source Array
Stationary CT
X-ray digital breast tomosynthesis (DBT)
The digital mammogram on the left shows 1 calcification. Slices from the tomosynthesis reconstructions,
shown in the 2 right images, show that one calcification is at 30 mm height in the breast, and the other at 47
mm. (From Hologic)
Sha_chang@med.unc.edu
UNC Argus 2.0 : Stationary DBT
Expected benefit: faster scanning time, better resolution, simpler design,
lower imaging dose
Nanotube Stationary Tomosynthesis (NST)
(Siemens)
Maltz, et al Med Phys 36 (5), May 2009
Artiste
• 52 x-ray sources:
4 banks and each has 13 sources
• Each x-ray source is individually
controlled
• ~ 5 sec. imaging acquisition time
for tomosynthesis and less for
multiple projection imaging
• A single portal imager is used
• Imaging during treatment!
CT
Coronal
Slice 1
Coronal
Slice 2
NST
Region
of better
resolution
CNT-based irradiation
technology development
Update
CNT FE based x-ray pixel beam micro-RT
(b)
Micro-CT-RT
Prototype(a)micro-RT
x
4.0cm
2D x-ray
pixel beam
array
z
y
Multi-array system
Sha_chang@med.unc.edu
Single array system
X-ray pixel beam array micro-RT
• Individual pixel beam
control for irregular
field shaping and IMRT
• micro-RT planning by
micro-PLUNC
• micro-CT-RT
integration for
fractionated IGRT.
6-pixel beam field
Pixel beam: 2mm
Sha_chang@med.unc.edu
CNT micro-RT dosimetry (MC simulation)
2mm XPBA
1cm field
Sha_chang@med.unc.edu
Tumor
(a)
Prototype CNT micro-RT system
X-ray pixel beam
(1-2 mm)
•5x10 pixel array
•Pixel beam size: 2mm
•1Ebergy: 100kV
•Dose rate: 1Gy/min.
(b)
Pillar (ceramics,φ 12.5mm)
Collimator (Cu)
Anode (25.4 um W foil)
Electron beam size at anode: 325 um
Distance: 12 mm
(Focusing electrode-Anode)
Focusing electrode
(Stainless steel plate: 2mm)
Spacer (Glass or Ceramics: 3 mm)
Gate (φ 25.4 um wire W mesh +
1 mm stainless steel plate)
Cathode (CNTs on Cr plus Cu layer)
Spacer (Glass: 150-200 um)
Radiation
SiO2 +Si
Assembled micro-RT.
Oncology
Physics & Astronomy
Image of prototype of multi-pixel micro-RT
Sha_chang@med.unc.edu
Cathode chip design and fabrication
5x5
5 x 10
Electrical connection pads
CNT cathodes
Sha_chang@med.unc.edu
Pixel beams are individually addressable
50 irradiation beams on
Electronic circuit
Selected 10 irradiation beams on
Sha_chang@med.unc.edu
This function results in electronical shaping
of tumor field for irradiation
Irradiation beams obtained
by individually controlling
Six pixel-beam field
To electronically form tumor shape for irradiation through
“turning on” a sub-set of the x-ray pixel beams.
Sha_chang@med.unc.edu
“NCI” irradiation pattern by electron and x-ray beams
through individual controlling of cathodes
Electron pixel beams
image
Energy: 30kV
2mm
Image from micro-RT
x-rays measured by
GAFCHROMIC film.
Sha_chang@med.unc.edu
CNT Multi-pixel micro-RT development
Challenges:
High voltage is technically challenging to
achieve in academic research labs;
High current (high dose rate) needs forced
anode cooling;
Need industry’s involvement after feasibility
demonstration.
Next Steps:
CNT based micro-CT-RT integration.
Single pixel microbeam device
UNIVERSITY OF NORTH CAROLINA AT CHAPEL HILL
AAPM 2006 Orlando Chang (30)
SCI dose and dose rate calibration
•
Dose is controlled by the number of emission current pulses;
•
Estimated dose rate range: cGy to 104 Gy per sec!
FWHM = 28 μm
Dose rate: 103
Gy/sec!!
20 μm
Measured by GAFCHROMIC film
Emission current: 2 μA; frequency: 100Hz; duty cycle: 5x10-4
UNIVERSITY OF NORTH CAROLINA AT CHAPEL HILL
AAPM 2006 Orlando Chang (31)
Cell irradiation demonstration (H2AX: DNA damage)
(rat fibroblast cells)
Neg. control
23Gy, 30keV electron beam
pos. control
Multi-pixel Film Irradiation
and Dosimetry
50 µm
FWHM: 40 um, dose: 29.1 Gy
1.45mm
Film Irradiation from 5x5 cathode
array UNIVERSITY
locations withOFallNORTH
pixels CAROLINA AT CHAPEL HILL
AAPM
2006 Orlando Chang (33)
interconnected
SUMMARY
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Carbon nanotube field emission X-ray technology is
capable of ultra-high temporal resolution
imaging/irradiation and novel multi-pixel source array
systems;
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CNT field emission based novel imaging systems
(micro-CT, Tomosynthesis IGRT, stationary breast
tomosynthesis), and irradiation systems (micro-RT,
multi-pixel single cell irradiation) are feasible;
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Industry involvement is essential to realize the full
potential of the technology (Xintek, Xinray, Siemens).
ACKNOWLEDGEMENTS
Researcher team:
Sigen Wang, Jerry Zhang, David Bordelon, Jared Snider,
Eric Schreiber, Adrienne Cox, et al.
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NIH-U54-CA119343-01 (Cancer Nanotechnology Center
of Excellence grant)
NIH-NIBIB (4R33EB004204)
NIH-NIBIB (4R33EB004204-03S1)
NIH-NCI (R21 CA118351-01)*
NIH (R21 CA128510-01)*
North Carolina Biotechnology Center*
UNC Lineberger Comprehensive Cancer Center
Department of Homeland Security (TSWG)
Xintek Inc. (UNC start-up company)
*: Irradiation device grant