production of radioisotopes: where it all begins! thomas j. ruth triumf vancouver, canada
TRANSCRIPT
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Production of radioisotopes: where it all begins!
Thomas J. Ruth
TRIUMF
Vancouver, Canada
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Radiochemical tracers
Probe biochemical systems by labelingcompounds with known biologicalbehavior.
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Tracer Principle
•Tracer behaves in a similar way to the components of the system to be probed.
•Tracer does not alter the system in any measurable fashion.
•Tracer concentration can be measured.
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Specific Activity
• Radioactivity per mass – MBq/mole
• To maintain tracer priniciple must have the highest SA possible.
• 370 MBq @ 370 GBq /mole = 1014 molecules
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Sources of radioisotopes:
Naturally occurring – 235U
Fission – 99Mo 99mTc
Neutron capture – 186Re
Charged particle – 123I
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Radioisotope production is truly Alchemy where you change one element into another!
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Choice of method
The best possibility for achieving high SA is through charged particle reactions.
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185Re + n = 186Re + 185Re(n,)186Re
18O + p = 18F + n18O(p,n)18F
Notation
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Excitation function
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R = In (1 – e-t)
WhereR – production rateI – beam flux – cross section(1 – e-t) – saturation factor
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Positron Emitters
Nuclide T1/2 (mins) Reaction Target Product
11C 20.3 14N(p,) [11C]CO2(gas)[11C]CH4(gas)
13N 9.97 16O(p,)15O 2.03 15N(p,n)
18F 109.7 18O(p,n) [18F]F2 (gas)[18F]HF (aqueous)
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Production Methods
Target Target Material Product Form
Gas 14N2, 1% O2 [11C]CO2
Gas 14N2, 1% H2 10% [11C]CH4
Gas [18O]O2 (95-98%) [18F]F2
Liquid [18O]H2O (88-98%) [18F]HF
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Gas Target
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Liquid Target
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Parameters
• target construction• target constituents• irradiation conditions
– energy
– current
– temperature
– pressure
– dose
• optimize yield and specific activity
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[11C]CO2
• small volume aluminum targets
• O2 may or may not be added
• H. J. Ache, A.P. Wolf, Radiochim. Acta Vol 6, p32, 1966
• primary products are CN and CO at low dose (<0.1 eV/molecule)
• higher doses radiolytically oxidize these to CO2
• typical dose 150 eV/molecule
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[11C]CH4
• initial work to produce HCN in target required flow-thru quartz body due to dose dependence and CN reactivity.
• large aluminum or small nickel targets reported to work well.– D.R. Christman et al. Int. J. App. Rad. Isot., Vol. 26, p435, 1975.
– G.-J. Meyer et al. Radiochimica Acta, Vol. 50, p43, 1990.
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[11C]CH4
• Reaction Pathway
N2 + H211C + N2 + H2
11CN
11CN + H2 HCN
HCN CH4 + NH3
protons
radiolysis
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[11C]CH4 at TRIUMF
• initial results with cylindrical target, 5% H2 very poor (30% theoretical)
• conical target, 10% H2 (50% theoretical)
• NH3 in equilibrium & only dependent on amount of H2
• residual fields show 11C produced but not extracted in gas phase
• Recently have starting using Nb target chamber with excellent yields
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[18F]HF
• first water target was Kilbourn et al. Int. J. Appl. Rad. Isot. Vol. 35, p599, 1984.
• target materials, titanium, silver, nickel, gold, plated– A.D. Roberts et al. NIM B99, p797, 1995.
– C. E. Gonzalez Lepara & B. Dembowski, Appl. Rad. Isot. Vol. 48, p613, 1997.
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[18F]F2
• An 18O2 Target for the Production of [18F]F2
R. J. Nickles, M.E. Daube, and T.J. Ruth,
Int. J. Appl. Radiat. Isot. Vol. 35, p117, 1984
– experience with 20Ne(d,18F + carrier 19F2
– subsequent irradiations > theoretical
– target wall acting as a holding pool for F
– NiF2 on target walls is not passive
– proton-only accelerators & 3x yield
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Nickles’ 4 Compartment Model
Non-reactive gases(CF4, NF3,…)
Atomic flourineF
MolecularflourineF2
NiF2 target surface
k1
k2
k3 k4 k5
k6 k7
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Two-shot Method
• target evacuated
• O2 released to target and irradiated
• O2 cryotrapped out
• target evacuated with mech. pump
• target loaded with 20-200umole F2 + inert gas (Ne, Ar, Kr, Xe)
• 18F2 released from target via isotopic exchange
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18O2 Gas Handling system
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[18F]F2
• several reports of single and double shot production methods implemented
• reported use of aluminum target bodies in 1991 by Bida et al. – Proc. of IVth Int. Workshop on Targetry and Target Chemistry.
• Development of an improved target for [18F]F2 production.A.D. Roberts, T.R. Oakes, and R.J. Nickles
Applied Rad. Isot. Vol. 46, p87, 1995
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[18F]F2
• advantages of aluminum:– stability
– passivation
– activation
– machinability
– cost
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010203040506070
%18F2
[18F]F2 yield vs. 19F2 conc.
mol 19F2
Electrophilic 18F from a Siemens 11MeV Proton-only CyclotronChirakal et al. Nucl. Med. Biol. Vol. 22, p111, 1994.
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[18F]F2 yield vs. Irradiation time
0
20
40
60
80
100
0 5 10 15 20 25
Recovery Irradiation (mins)
% y
ield
A.D. Roberts, T.R. Oakes, R.J. NicklesDevelopment of an improved target for [18F]F2 production.App. Rad. Isot. Vol. 46, p87, 1995.
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[18F]F2
• Proton Irradiation of [18O]O2: Production of [18F]F2 and [18F]F2 + [18F]OF2
A. Bishop, N. Satyamurthy, G. Bida, G. Hendry, M. Phelps, J.R. Barrio
Nucl. Med. Biol. Vol. 23, p189, 1996
• targets of aluminum, copper, gold plated copper, nickel, cone and cylinders
• single and two shot• multiple recoveries
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Multiple Recoveries
A. Bishop et al., Nucl. Med. Biol. Vol. 23, p189, 1996
0
10
20
30
40
50
60
1 2 3 4
Step
%[1
8F]
Rec
over
ed
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Choice of Production Method
• the threshold energy for initiating the reaction
• the energy where the maximum cross section is found
• the physical properties of the target material
• the physical properties of the product
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Choice of Production Method -continued
• the chemical properties of the target
• the chemical properties of the product
• the ease of separation of the product and target
• and the ability of converting the product into a useful labeling form.
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Confounding issues
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In Target Chemistry?
For a 15 cm target at 10 atm N2 and a 10.5 MeVproton beam..
Heselius, Abo Akademi
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Ep= 13.0 MeV
P0= 300 psi
Havar window
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90% Thick
Ep= 13.0 MeV
P0= 300 psi
Havar window
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75% Thick
Ep= 13.0 MeV
P0= 300 psi
Havar window
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50% Thick
Ep= 13.0 MeV
P0= 300 psi
4.2 MeVHavar window
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He cooling foil from TR13 Target
Note heat mark
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Courtesy of John Lenz
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Courtesy of John Lenz
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Simulation Experiments
Test jig:
• Ø 10 mm copper rod with imbedded heater
• Low heat conductive isolation (Vespel)
• Thermocouple at window center
Data measurement:
• Record He flow
• Record temperature during heat/cooling cycle: Activate heat load, when T equilibrates (15 min) deactivate heat load
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Performance of "Ideal" & Original Helium Windows
0
20
40
60
80
100
120
0 5 10 15 20 25
Time (minutes)
Te
mp
era
ture
(d
eg
. C)
Ideal 1mm nozzle (flow 39)
Ideal 1.3mm nozzle (flow 73)
Ideal 1.5mm nozzle (flow 90)
Original window (flow 108)
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Water Cooled Grid Target
Roberts & Barnhart, U. Wisc.
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Yield Comparisons
00.10.20.30.40.50.60.70.80.9
0 10 20 30 40
Irradiation Time (min.)
Rat
io (%
theo
r;
11C
H4/11
CO
2)
Al Cone
Ni cone
SS cyl.
Al cyl.
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Performance Ratio (CH4/CO2 Yields)
0
0.2
0.4
0.6
0.8
1
5 20 30
Irradiation Time (min)
Yie
ld R
atio Ni Plated Al
Large Volume Al
Stainless Steel
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11CH4 Yield vs Irradiation Time
0
200
400
600
800
1000
1200
1400
1600
1800
0 10 20 30 40 50 60 70
Time (minutes)
Rad
ioac
tivi
ty (
mC
i)
Theoretical @ 92mCi/A
Nb bodied target
Aluminum bodied target
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Accelerator Production of High Specific Activity Therapeutic Radionuclides:
Production of High LET Radioisotopes at
TRIUMF-ISAC
Thomas J. RuthUBC/TRIUMF PET Program
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"It's not for content but for appearance" Pierce
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Candidate radionuclides for radioimmunotherapy:
47Sc 64Cu 67Cu
90Y 105Rh 103Pd
111Ag 124I 142Pr
149Pm 153Sm 159Gd
166Ho 177Lu 186/188Re
194Ir 199Pt 211At
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Accelerator Production
• Target Z Product Z
• High Specific Activity
• Low Energy - Fewer By-Products
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Choice of Accelerator
• Commercial cyclotrons: 30 MeV• University based cyclotrons: 10 - 50 MeV• Hospital based PET accelerators: 3 - 19 MeV• National Labs: 100 - 500 MeV
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High Energy Facilities• Brookhaven National Lab Lab, US
– 200 MeV, 145 A
• Los Alamos National– 100 MeV, 125 A
• Institute of Nuclear Research, Russia– 160 MeV, 100 A
• TRIUMF, Canada– 13, 2 x 30, 42, 70, 500 MeV, 50 A – 1 mA
• National Accelerator Centre, South Africa– 200 MeV, 100 A (p & d, HI)
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Limitations of High Energy Facilities
• Availability
• Scheduling
• Range of products
• Sp. Act. affected by co-production of isotopes.
• Reliability
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How is 64Cu made?
Reactor Nat Cu ARI Poor Specific Activity
Cyclotron 64Ni(p,n)64Cu Research High Specific Activity
64Ni(d,2n)64Cu Research High Specific Activity64Ni 0.93 % nat. abund.Commercially Viable
Questionable
68Zn(p,αn)64Cu Research High Specific ActivityBoothe 1991 68Zn 18.6 % nat abund.
Target for 67GaCommercially Viable
SV Smith, ANSTO
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68Zn(p,n)64Cu
High Specific Activity 64Cu> 3000 Ci/g on delivery (> 24 hours EOB)
Half Life 12.7 hr
Positron Emitter
67Cu (1% at EOB)High Purity (chemical and radionuclidic) 64Cu
Half-life 2.580 days
Gamma emitter SV Smith, ANSTO
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77Br Production, t1/2 = 2.4 d
• Possible reactions:– 75As(,2n) @ 27 MeV
– 77Se(p,n) @ 13 MeV
– 78Se(p,2n) @ 24 MeV
– 79,81Br(p,xn)77Kr @ 45 MeV
– natMo(p,spall.) @ >200 MeV
• Natural abundances:– 77Se = 7.6%; 78Se = 23.6%
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124I - Potential Radiotoxic Nuclide
• t1/2 = 4.14 d
• + emitter• Production
– 124Te(p,n)124I @ 13 MeV
– 125Te(p,2n)124I @ 25 MeV
• Natural abundance: – 124Te = 4.79%
– 125Te = 7.12%
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211At Productiont1/2 = 7.2 h
• Possible reactions– 209Bi(,2n) @ 28 MeV– 209Bi(7Li,5n)211Rn @ 60 MeV– 232Th(p,spall.)211Rn @ >200 MeV
• 211Rn t1/2 = 14.6 h
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Decay of 211Rn and growth of 211At. Optimal recovery at about 16 hours.
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Estimated Production of 211Rn
• Target - UO2/C - 3.4 g
• Yield of 211Rn - 1.5 x 107nuclei/s/A• Translates to 0.027 mCi/h
Conclusion - Need at least 3 orders of magnitude improvement to have any clinical utility.
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• 100 A provides 2 orders of magnitude,• thicker target/beam optics gains a factor of 2 or
3 (or more),• better transport system from target to ECR
gains a factor of 2 at most,• better ionization efficiency could provide
another factor of 2 or 3.
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High Specific Activity 186Re
• Chemistry of Re similar to that of Tc
• t 1/2 = 90.6 h
• I = 92% Emax= 1.1 MeV
• I= 9% E= 137 keV• Max. Theoretical Sp. Act. – • 1.28 X 106 GBq/mmol• Reactor Produced Sp. Act. - 37 GBq/mmol
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Accelerator Production of 186Re
• 186W(p,n) 0.05 mCi/ Ah @ 18 MeV
• 186W(d,2n) 0.2 mCi/Ah @ 20 MeV• 197Au(p,spall.) 0.025 mCi/Ah @ 500
MeV• natPt(p,spall.) 0.2 mCi/Ah @ 500 MeV• natIr(p,spall.) 1.6 mCi/ Ah @ 500 MeV
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Reactor produced radionuclides that potentially could be prepared via on-line isotope separator
system:
105Rh 109Pd 111Ag
142Pr 149Pm 153Sm
159Gd 166Ho 177Lu
186Re 188Re 194Ir
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Production of Selected IsotopeIsotope ISOLDE Yield
(atoms/A /s) Projected ISAC Yield
mCi/100A day 105Rh 1.5 x 108 190 109Pd 2.4 x 109 790 142Pr 1 x 107 23
149Pm 4.3 X 105 0.4 153Sm 8.7 x 107 83
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ION BEAM
60 keV
P l a s t i c – f o i l (PE, polyether, MYLAR, KAPTON …)
Implantation
Implantation into plastic material open channelsmetal foils channels closedII
G-J Beyer, CERN
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Feasibility of 125Xe Implantation at TRIUMF for the Preparation of 125I Brachytherapy Sources
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125Xe Collection Box at TISOL
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Critical Factors on 125I Implantation
• Production rates of 125Xe• Implant system efficiency• Stability from losses of implanted species • Radiobiological effectiveness
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Production rates of 125Xe
• Based on published data* the yield of 125Xe from a 50 g/cm2 Cs target is 0.7 Ci/hr for a 10 A proton beam.
• The 125Xe is quantitatively released.• Due to half-life differences the yield of 125I is 0.012 of
125Xe.
* JS Vincent, J. Radioanal. Chem. 65:17-29 (1981)
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Implant system efficiency
• 125Xe is ionized via ECR ion source• Implantation potential 12 kV & 22 kV• Mean range in Fe is 0.047 • Foils tested include Fe, Ti, Au• Efficiency through the system to implantation
was 23%.
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Stability from Losses of implanted Species
• Foils were soaked in saline at room temperature for 3 days.
• Soaked in saline at 55 C for 3 days.• Solutions taken to dryness and counted for 125I
radioactivity.• All foils tested had quantitative retention of
radioactive species..
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Conclusions
• System efficiency = 23%• Cs target has high production rate• Estimated yields = 2 mCi/hour• Stable implant
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Many clinically relevant therapeutic nuclides can not be produced in high specific activity from reactors and the accelerators can not produce sufficient quantities for large scale usage.
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Problem:
• Reactor production - Low Specific Activity.
• National Lab Accelerators - Capacity for large scale production insufficient.
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Possible Solution:
Production in reactors or spallation sources with off-line isotope separation.
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Conclusions
• Many radionuclides can be produced at low energy cyclotrons distributed throughout NA, Europe and Asia.
• High Energy facilities can not be relied upon for the bulk of clinically relevant radionuclides.
• Alternative methods of production and isolation need to be explored.
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Acknowledgements
I wish to thank the many colleagues have contributed to the work, ideas and slides presented here, especially Gerd Beyer, Suzanne Smith, ANSTO and Geneva John Vincent, TRIUMF.
TRIUMF is supported through a contribution fom the National Research Council of Canada.
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TRIUMF, Vancouver, Canada
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There's nothing left . . . but to get drunk. F. Pierce