Upload
stephany-creekmore
View
220
Download
2
Tags:
Embed Size (px)
Citation preview
RADIOISOTOPE PRODUCTION
Background Imaging techniques Reactor production Accelerator production The Moly Crisis Radioisotopes
Historical background
Nuclear medicine dates back to as early as the 1800s with the discovery of naturally occurring radioisotopes and the use of x-rays.
Rapid advancements
such as the invention of the cyclotron lead to the birth of modern nuclear medicine as we know it today
Nuclear reactors also played a role in the development of nuclear medicine as a method of creating radioisotopes
Radioisotopes of all decays alpha, beta and gamma are used for both treatment and diagnostics in nuclear medicine
Focus here is on diagnostic isotopes that are either gamma or positron emitters. SPECT or PET
Therapy alpha
Diagnostic gamma
DiagnosticBeta +
SPECT Patients are injected with a gamma emitting isotope
attached to a targeting ligand for uptake in specific areas of the body
Different length half-lives are suited to different types of procedure e.g. uptake time
2D and 3D maps of an area can be created using a computer model of the signals received.
PET Similar to SPECT but maps created
from signals of secondary gammas from positron/e- annihilation
Production methods Once radioisotopes could be manufactured
(reactor or accelerator) two different supply methods became available
Direct production
Generator production
Direct Production
The direct production of a radioisotope due to the bombardment of a target isotope by a projectile such as a proton, neutron, alpha or deuteron.
The direct production of a radioisotope as a by product of the neutron bombardment inside the target of a research reactor.
Generator production The production of the radioisotope as
the decay product of another radioisotope.
Most commonly 99Mo – 99mTc Parent isotope is collected in a column
where the daughter isotope can be eluted using various types of solution dependent on isotope and application.
Isotope is then mixed in a pre-prepared kit to form the drug administered to the patient
Rector Production Radioisotopes can
also be produced as a by product of spent reactor fuel
Currently the most common production route
However this supply is under threat due to an aging fleet and no replacements
MOLY CRISIS
In 2010 the main reactors went off line for an unexpected extended maintenance.
As a result over 80% of the worlds nuclear imaging procedures had to be postponed or cancelled.
The current fleet is old and close to retirement with no back up currently in place another crisis is looming
Tc-99m
Half-life: ~6hrs, decay: 140keV gamma The most common of the medical
radioisotopes primarily due to ease of production
Production: Generator via Mo parent – a by product of nuclear reactors
Used for a range of SPECT procedures including: bone, brain, blood, lung scans, heart and tumours
Solutions to the crisis
New reactors?
Accelerators? Current cyclotrons? Linacs?Low energy machines?
Other isotopes?
Some factors to consider when determining the most suitable production methodHalf-life of the isotope in question: is it long enough
for direct production, on site or regional supply?Cleanliness of the reaction: how many contaminants
are produced alongside the radioisotope of interest and how easily can they be extracted?
Natural or enriched targets? How much target material is there? How easily can a target be manufactured and processed?
Energy range of incident particlesCheapest supply of incident particle How can we make an isotope more widely available
New Reactors
Accelerator Approach
Solid Targets (1)
Thin and thick Foil Elemental or mixed composition typically
oxide Created with electroplating
Solid Targets (2)
Thick pellet targets Elemental or mixed composition typically
oxide Created by compression
Liquid Targets
Water or molten metal Compound targets Contained by metal casing often
aluminium or nickel Flowing targets aid in cooling
Gas Targets
Pressurised gas housed in a metal container
Electron Machines Canadian Light Source part of a
commission by the Canadian government to find accelerator methods to replace NRU
Uses Bremsstrahlung from an electron linac (35MeV)
Principle has been successfully demonstrated
100Mo(γ,n)99Mo
Proton Machines TRIUMF facility part of the same
commission as CLS Uses ~20MeV Proton Cyclotron Successfully demonstrated the most
favoured approach to accelerator based 99mTc production
100Mo(p,2n)99mTc
TRIUMF Target
Pellet target Target recycling
Low energy accelerators (1) ns-FFAG Ep <16MeV Can be used with thin or thick targets
ONIAC - Siemens Electrostatic DC accelerator ~10MeV Can be used with thick or thin, solid or
liquid targets Proton or deuteron beam
Low energy accelerators (2)
Low Energy 99Mo/99mTc Production
Direct
100Mo(p,2n)99mTc
98Mo(p,γ)99mTc
Generator
100Mo(p,pn)99Mo
100Mo(p,2n)99mTc Route with the most potential as focus of
the TRIUMF studies Cross-section peaks above the energy
range of interest for low energy production
More efficient at higher energies as proved by TRIUMF is it worth taking forward?
98Mo(p,γ)99mTc
Highest ratio of 99mTc to 99Tc Clean product Very low threshold, only viable for
Ep < 5MeV However total yield not large enough for
medical quantities
Other SPECT isotopes Iodine-123 half-life:13.2hrs Used for thyroid imaging and treatment Current Production: 124Te(p,2n)123I
Internal solid powder targetsTargets in both elemental and oxide form
Strontium-87m half-life:2.8hrs Used for bone imaging
Current production: Via generator 87Y (half-life:79.8hrs)
87Sr(p,n)87Y – 87mSr Elemental or compound target (SrCl2)
Ep ~ 20MeV
natRb(a,xn)87YEa < 26MeV
Gallium-67 Half-life: 3.3 days Uses: Long half-life useful for slow
uptake tumour imaging Production: natZn(p,X)67Ga
PET isotopes
Typically short-lived positron emitting isotopes
Both complimentary and competitive with SPECT
F-18
Half-life: 110mins Uses: brain scans, cardiology and
tumour monitoring. FDG the primary F-18 drug Production: 18O(p,n)18F, 20Ne(d,a)18F,
20Ne(p,2pn)18F Both liquid and gaseous targets used
18O(p,n)18F
Liquid target of H218O housed in a metal
container or gaseous 18O Near threshold proton beam Ep<15MeV F-18 extracted as aqueous fluoride
20Ne(d,a)18F
Gas target of H2Ne so that F-18 is created as H18F which can be extracted as aqueous fluoride
C-11
Half-life: 20mins Uses: similar to F-18, easily inserted into
many biological structures replacing the existing carbon
Production: 14N(p,a)11C Gas target
Cu-64
Half-life:12.7hrs Uses: joint therapy and diagnostic tool Production: 64Ni(p,n)64Cu, 68Zn(p,an)64Cu Ep ~ 16MeV
Ga-68
Half-life:68mins Uses: similar to F-18 but preferred for
areas with high background FDG uptake such as brain tumours
Production: currently via generator 68Ge(half-life:270days)
natZn(a,X)68Ge,
natGa(p,X)68Ge
Low energy direct production of 68Ga enriched single isotopic solid target Ep ~ 10MeV 68Zn(p,n)68Ga
Summary
Radioisotopes are a vital life saving tool Many methods of manufacture, the most
suitable system is determined by the isotope in question i.e. half-life, contaminants, target material abundance
Currently dependent on reactor based methods which lead to supply crisis
Summary (2)
Community looking to expand accelerator based methods
Introducing potential new isotopes
Questions?