Topic 2-Production of Radionuclides & QA QC

  • View
    221

  • Download
    4

Embed Size (px)

Text of Topic 2-Production of Radionuclides & QA QC

  • Production of Radionuclides

  • All radionuclides commonly

    administered to patients in nuclear

    medicine are artificially produced

    Most are produced by cyclotrons,

    nuclear reactors, or radionuclide

    generators through bombardment or

    fission

  • 1. Cyclotrons

    Cyclotrons produce radionuclides by

    bombarding stable nuclei with high-

    energy charged particles

    Most cyclotron-produced radionuclides

    are neutron poor and therefore decay by

    positron emission or electron capture

  • >Specialized hospital-based cyclotrons have been developed to produce positron-emitting radionuclides for positron emission tomography (PET)

    >Usually located near the PET imager

    because of short half-lives of the

    radionuclides produced

  • 2. Nuclear Reactors

    Specialized nuclear reactors used

    to produce clinically useful

    radionuclides from fission products

    or neutron activation of stable

    target material

  • >Uranium-235 fission products can be chemically separated from other fission products.

    >Concentration of these carrier-free

    fission-produced radionuclides is very

    high

  • Neutron Activation

    Neutrons produced by the fission of

    uranium in a nuclear reactor can be

    used to create radionuclides by

    bombarding stable target material

    placed in the reactor

  • >Process involves capture of neutrons by stable nuclei

    >Almost all radionuclides produced

    by neutron activation decay by

    beta-minus particle emission

  • 3. Radionuclide Generators

    A generator is a self-contained system housing a parent/daughter mixture in equilibrium.

    There must be a method of removing the daughter and leaving the parent behind to regenerate more daughter activity.

    It is designed to produce the daughter for some purpose separate from the parent.

  • Generators produce certain short-lived radioisotopes on-site which cannot be shipped by commercial sources.

    To be useful, the parent's half-life must be long compared to the travel time required to transport the generator to recipient.

    The typical shelf-life of a Mo/Tc generator is 2 weeks, as is the expiration date.

  • the process of removing the daughter

    from the generator is referred to as

    elution;

    the solution used to remove the

    daughter is called the eluent;

    and the solution collected from the generator containing the daughter radioisotope is called the eluate.

  • Technetium-99m has been the

    most important radionuclide used in

    nuclear medicine

    Short half-life (6 hours) makes it

    impractical to store even a weekly

    supply

  • Supply problem overcome by obtaining parent Mo-99, which has a longer half-life (67 hours) and continually produces Tc-99m

    A system for holding the parent in such a way that the daughter can be easily separated for clinical use is called a radionuclide generator

  • 1. Generator output must be sterile and pyrogen-free.

    2. The chemical properties of the daughter must be different than those of the parent to permit separation of daughter from parent.

  • 3. Generator should be eluted with 0.9% saline solution and should involve no violent chemical reactions.

    4.Daughter isotope for diagnostic studies should be short-lived gamma-emitting nuclides.

  • 5. Inexpensive, effective shielding of

    generator, minimizing radiation dose to

    those using it.

    This is easy to accomplish since lead is very dense and therefore a good attenuator of radiation.

  • DRY column generator

    The saline supply is in a 30-ml bottle/vial for elution

    Because saline used never exceeds 20ml, up to 10ml of air follow the saline through the fluid path, effectively drying the column

  • WET column generator

    The saline supply is a 500ml bottle and is an integral part of the generator

    Once elution is completed, the fluid path is filled with a saline for the life of the generator and the alumina column is always saturated with 0.9% NaCl solution

  • Equilibrium

    is a condition established in a parent/daughter mixture when both parent and daughter are radioactive and when the daughters half-life is shorter than that of the parent.

    if the daughters half-life exceeds that of the parent, equilibrium will never be reached.

  • Transient Equilibrium

    -is a condition reached when the half-life of the parent is approximately 10 times greater than the half-life of the daughter.

  • Secular Equilibrium

    -if the half-life of the parent is very much longer than that of the daughter (e.g., more than 100 longer).

  • 99Mo/99mTc GENERATOR: PRINCIPLES OF OPERATION

    1. Prior to shipping the generator to the

    Nuclear Medicine Department, 99Mo

    sodium molybdate is immobilized on a

    column of alumina (Al2O3; aluminum

    oxide).

  • 2. 0.9% saline solution (the eluent) is

    passed through the column and Na

    pertechnetate, the daughter of 99Mo

    decay, is eluted from the column with

    high efficiency due to its almost total

    lack of affinity for alumina.

  • 3. The pertechnetate is collected in a

    shielded, evacuated sterile vial and

    must undergo quality control testing,

    then must be calibrated prior to use. It

    is referred to as the eluate.

  • 99Mo/99mTc GENERATOR

    is considered to be the workhorse of all generators and is ideal with no significant limitations

    used in almost 80% of nuclear scan performed

  • Commonly Transported Radioisotopes

    *Americium-241= Diagnose thyroid disorders, smoke detectors.

    *Cesium-137= Cancer treatment.

    *Iodine-125,131= Diagnosis & treatment liver, kidney,heart, lung and brain.

    *Technetium-99m=Bone and brain imaging; thyroid and liver studies; localization of brain tumors.

  • 6. Low radiation dose

    7. Safe

    8. Convenient

    9. Cost-effective

  • QC program is especially important in

    two main areas:

    Instrumentation

    Radiopharmaceutical preparation

  • Instrumentation:

    Well counters

    Dose calibrators

    Thyroid probes

    Gamma camera

  • QC for Gamma Camera

    Spatial resolution Weekly

    Uniformity Daily (before first patient)

    Image linearity Weekly

    Energy resolution Annually

    Count rate response Annually

    Sensitivity Annually

    Collimator integrity Annually or when suspicious of damage

    Formatter performance Annually

    Whole-body accessory Annually

    Window setting For each patient

  • Radiopharmacy

    Generator and radionuclide purity

    Radiochemical labeling

    Sterility

  • Operation and routine QA

    Energy discrimination windows

    must be adjusted to center them on

    the photopeak or photopeaks of the

    desired radionuclide

  • Operation and routine QA (cont.)

    Uniformity of the camera should be assessed daily and after each repair

    May be made intrinsically by using a Tc-99m point source

  • Images must contain enough counts that quantum mottle does not mask uniformity defects

    Uniformity test will reveal most

    malfunctions of a scintillation

    camera

  • Other QA

    Spatial resolution and spatial

    linearity should be assessed at

    least weekly

    Efficiency of each camera head

    should be measured periodically

  • Complete evaluation at least annually

    Include multienergy spatial registration and count-rate performance

  • Peaking

    Counting Rate

    Field Uniformity

    Spatial Resolution

    Spatial Linearity

    Sensitivity

    QC for Gamma Camera

  • Gamma Camera Quality Control

    QC Procedure Frequency

    Peaking Daily & before each new radionuclide used

    Counting rate limits Daily

    Field uniformity Daily, after repair

    Spatial resolution Weekly, after repair

    Spatial linearity Weekly, after repair

    Sensitivity Quarterly

  • Energy discrimination windows

    must be adjusted to center them

    on the photopeak or photopeaks

    of the desired radionuclide.

    QC Procedures for Gamma Camera

    Peaking

  • Peaking may be done manually

    by adjusting the energy window

    settings while viewing the spectrum

    or automatically by the camera

    Should be peaked before first use

    each day and before imaging a

    different radionuclide

  • Small source used to

    peak camera; radiation

    emitted by the patient

    would have a large scatter

    component.

  • Sensitivity of a gamma camera generally decreases with increased amounts of activity.

    During the high activity the detector is paralyzed & cannot count.

    Dead Time is the systems inability to count

    QC Procedures for Gamma Camera

    Counting Rate Limits

  • Field Uniformity

    Refers to the gamma cameras ability to detect a uniform source of radiation

    Uniformity depends on the uniform response of the NaI crystal & the PMTs.

    QC Procedures for Gamma Camera

  • Intrinsic Uniformity Flood

    A. Field Uniformity Flood B. Non-uniform Flood