Metallic nanoparticles in proton
therapy: how does it work ?
Dr. Anne-Catherine Heuskin
University of Namur
3rd BHTC workshop
Why do we use nanoparticles in
radiation therapy ?
Grail  increase biological effects in tumors and spare
healthy tissues
RARAF 1Gy/min - UNamur CL
RARAF 8.7 Gy/min - RARAF CL
RARAF 0.1 Gy/min - UNamur CL
UNamur 1 Gy/min - UNamur CL
1
Healthy cells
SF
0,1
A549 - a (100 keV/µm)
0,01
Cancerous cells
0,0
0,5
1,0
Dose (Gy)
1,5
2,0
Nanoparticle sensitizers
Dorsey et al. Transl Cancer Res 2013
Evidence with X-rays
Bladder cancer cells with 250
kVp X-rays and 50 nm GNPs
Glioma cells with 4 Gy X-rays
Jeynes et al. Phys Med Biol 2014
Dorsey et al. Transl Cancer Res 2013
Evidence with X-rays
Mice with GBM and 20 Gy RT
Dorsey et al. Transl Cancer Res 2013
Supposed mechanism
• Photoelectric effect
predominant for low kV
• Can produce energetic
secondary electrons
• Dose enhancement
• Less effect in MV range
2nd
electrons
Auger
electrons
Mesbahi et al. Rep Pract Oncol Radiother 2010
Reactive Oxygen
Species (ROS)
X-ray
Fluorescence
photon
X-ray
Long range effect
and
Short range effect
Can we do the same with protons ?
•2 MV terminal voltage (4 MeV H+, 6 MeV He2+, 12 MeV C5+)
• Multi-ions
• DC beam: DC ion sources and 100 V ripple on 2 MV.
• “Originally” designed for material analysis
TiH2 + (C)
+ Cs
SINIX
ion source
(H-, C-)
Duoplasmotron
ion source
(He+)
He+
Electrostatic lenses
Power
supply
amplification
Lithium electron adder
canal (He+> He-)
H+, He++, C5+
Stripper canal
Electrostatic lenses
+HV
Low energy
magnet
Faraday cup
& BPM
H-, C-, He-
Low energy acceleration High energy acceleration
RBS analysis
chambre
ERD/RBS analy
chambre
& Irradiation sta
UHV analys
chambre
Accelerating
tube
Implantatio
chamber
Low energy protons
Broad beam: Statistical hit of cells
We “play” with LET
e
Débit d
1,0
0,8
y/min)
dose (G
0,6
0,4
0,2
0,00
2
10
4
X
8
(m
6
m
)
4
8
10
2
Y
6 )
m
(m
Uptake in cancer cells
Blue area : Nucleus staining
Red area : Actin staining
Green dots : gold nanoparticles
and aggregates
A431 cells (Epidermoid carcinoma) at
UNamur
0.5 pg/cell
Evidence with protons
Epidermoid carcinoma with low energy protons
0,45
1
Difference of fitted data (AuNPs_5 nm)
Difference of fitted data (AuNPs_10 nm)
+
H , E=1.3 MeV LET=25 KeV/µm
0,40
Amplification ratio
Surviving Fraction
0,35
0,1
0,30
0,25
0,20
0,15
0,10
A 431
A 431+ AuNPs (5nm, 0.05 mg/mL, 24h incub.)
A 431+ AuNPs (10 nm, 0.05 mg/mL, 24h incub.)
0,01
0
1
2
Dose (Gy)
0,05
0,00
3
0,0
0,5
1,0
1,5
2,0
Dose (Gy)
See poster of Dr. Li
/!\ Generally, less pronounced effect
2,5
3,0
Mechanisms of action with protons
Yes but shorter range than X-ray
2nd
electrons induced
Auger
electrons
X-ray
Fluorescence
photon
Unlikely for low energies
But probably relevant for
SOBP
Short range
Reactive Oxygen
Species (ROS)
Charged
particle
Localized effect
Localized effect compared to X-rays
What is the dose increase ?
Is there a significant physical effect ?
Geant4 single nanoparticle irradiation
• Geant4 toolkit to track particles in matter
• Input data based on in vitro experiments
• Nanoscale (nanoparticle in water) and microscale (cell) approaches
Core + coating
H2O
H2O
H2O
Gold core
• Various diameters
• Various materials
• 1.3 or 4 MeV protons
• Secondary electron scoring
• Inside NP
• At NP surface
• Linear energy transfer (LET)
profile
Gold or titanium core
1.3 MeV protons
Auger transition
in titanium
Low energies lost in bulk
Auger for lower Z
Number of emitted electrons
Yield of secondary electrons at NP surface compared to water (1.3 MeV
protons)
Material
Pt
Au
Au Auger off
Ta
Hf
Zr
Ti
Ti Auger
off
water
Yield
1.40
1.27
1.27
1.16
0.94
1.00
1.53
1.27
1.00
Mean E
(keV)
0.94
0.94
0.94
0.98
0.98
0.70
0.42
0.47
0.23
Size effect
Gold
Yield per incident proton
at NP surface
Proportion trapped in
bulk
5 nm
10 nm
25 nm
50 nm
0.19
0.37
0.61
0.72
0.50
0.73
0.91
0.96
LET profile
5 nm gold nanoparticles irradiated by 1.3 MeV protons
Au
Au + PEG
Low energy
secondaries
from coating
Au + PEG (auger off)
Water equivalent
Local LET ↗↗ in the vicinity of gold nanoparticles !
 Does this explain the increase in cell killing ?
Nanoscale approach
• Pt, Au best emitters
• Also Ti because of Auger
emission
• Large NP  high selfabsorption but still more
efficient at 50 nm
• Coating  low energy
contribution
• Geant4 limitations (Auger
cascade and low energy
cross sections)
Cell geometry
Nanoscale (nanoparticle in water) and microscale (cell)
approaches
Yellow: interactions
X-Ray emission
2nd e- emission
Scattering
Proton, 1.3 MeV
GEANT4 single cell irradiation
Required
dose (Gy)
Proton only
(Gy)
SD
Proton + 10 nm
gold NP (Gy)
SD
0.5
0.499
0.005
0.502
0.008
1
1.013
0.010
1.023
0.006
2
2.023
0.005
2.033
0.025
3
3.03
0.014
3.053
0.015
• 0.5 pg/cell  49 500 gold nanoparticles (white random
spots)
• Total surface area = 3.89 µm² (vs 322 um² for the cell)
• 3Gy: 240 protons, and only 2.85 protons hit GNP
1 % proton in GNP for a 50 % increase in cell death ?
So how does it work ?
• Local increase in LET with the presence of gold nanoparticles
• But marginal physical effect: a few are actually irradiated !
• Biological or chemical phenomena ? Local increase of reactive
oxygen species ? (see talk of S. Penninckx)
• Thermal effect ?
Local increase in temperature near a proton track
Proton 1,3 MeV
Proton 1,3 MeV + gold
nanoparticles
35°C
260°C
Melting temperature of DNA ≈ 85 °C
In cytoplasm ? Integrity of proteins is
compromised
UNamur irradiation facility
• Low energy particle accelerator is a
convenient tool
• Bottow up approach that supports clinical
science.
• Helps to understand and evaluate new clinical
procotols
• Our radiobiology platform is available for
experiments.
[email protected]
[email protected]
Acknowledgments