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PH3704- Pharmaceutical technology > Radiopharmaceutics > Flashcards

Radiopharmaceutics Flashcards

1
Q

What is a nuclear medicine

A
  • X-rays show anatomy, but a poor indicator of function
  • Nuclear Medicine scans give poor anatomical detail but do show function
  • Radiopharmaceuticals are a combination of
  • Useful Molecule + Radioactive isotope
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2
Q

Gamma camera

A
  • Gamma photons are emitted by the patient due to medicine/diagnostic agent we injected- this hits the crystal of the camera causing the crystal to scintillate which is picked up by detectors
  • Colinator- these are small bits of lead which only allow gamma photons at a certain angle to hit the crystal allowing more accurate imaging (due to photons being given off in random direction)
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3
Q

Low radiation dosage to patients

A
  • Short physical half-life
  • Short biological half-life
  • Nature of radioactive decay
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4
Q

Philosophy of radiation protection

A
  1. All exposures shall be justified
    • Benefit gained outweighs risk involved
  2. All exposures shall be kept as low as reasonably practicable (ALARP)
  • We are exposed to radiation at all times- Cosmic radiation, radon gas, buildings, food stuffs
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5
Q

Radiation measurement unit

A
  • A measure of radiation energy in tissue
    • Sievert (Sv)
    • Use 1/1000 (milliSievert- mSv)
    • Or 1/1,000,000 (Micro Sievert- uSv)
    • A measure of radiation within the tissue
  • Natural radiations
  • Average for UK 2.5 mSv per year
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6
Q

Radon- Cornwall

A
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7
Q

Airline staff

A
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8
Q

Radiation Effects

A
  • Main concern is carcinogenesis
  • Assume a risk, whatever the dose
  • Radiation risk
  • Taking all factors into account risk of 1 in 15,000 for 2mSv
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9
Q

Radiation effects

A
  • Main concern is carcinogenesis
  • Assume a risk, whatever the dose
  • Radiation risk
  • Taking all factors into account, risk of 1 in 15,000 for 2 mSv
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10
Q

Compare with other risks

A
  • Smoking 10 a day- 1 in 200
  • Sea-fishing- 1 in 500
  • Mining- 1 in 7,000
  • Home accidents- 1 in 10,000
  • Road accidents- 1 in 10,000
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11
Q

Limiting Radiation Exposure

A
  • Time- keep to a minimum
  • Distance
  • Shielding- make sure you use right shield
  • SOPs must incorporate
  • Staff Training
  • Monitoring
  • Feedback
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12
Q

Inverse Square Rule

A
  • Distance is very important- it follows a sqaure root rule
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13
Q

Units

A
  • Becquerel- Rate of disintegration (1 d.p.s)
    • Says nothing about radiation dose to patients or workers
    • Curie in the US- 1 MilliCurie= 37 MBq
  • Gray (Gy)- S.I unit of absorbed dose
    • 1 joule of energy absorbed per Kg tissue
  • Sievert (Sv)- dose equivalent
    • Sievert = gray x quality factor (QF)
    • For Beta and Gamma emitters, QF =1
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14
Q

Types of radioactive decay

A
  • Alpha (a)
  • Beta (B)
  • Gamma (G)
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15
Q

Mechanisms of decay

a-particles

A
  • He nucleus- charge +2
  • Comparatively large- collide with tissue, give up their energy, cause ion pair (5000 cm-1)
  • Considerable damage in small area
  • Range in tissue of a few mm
  • Can easily be shielded
  • NO role in diagnostic agents, but have potential for therapeutic use
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16
Q

B- particles

A
  • Can have negative or positive charge
  • Smaller than a-particles- less interaction with tissue (50 ion pairs cm-1)
  • Less damage and greater range in tissue
  • Range can be up to several cm- depends on energy Emax and Emean
  • Valuable for therapy, but not diagnosis
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17
Q

B+ particles

A
  • Known as positrons- antimatter
  • Immediately after emission from nucleus, they interact with B- particle
  • Annihilation reaction- matter is converted into energy
    • B- + B+ => 2 gamma
  • Energy of each gamma = 511 keV, emitted at 180o to each other
  • Valuable in diagnostic procedures
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18
Q

Gamma rays

A
  • Electromagnetic radiation- not particles
  • Less interaction with tissue- hence why good in diagnosis, cause less damage, have greater range in tissue
  • Energy of emitted gamma rays constant for a given radionuclide
  • Valuable for diagnostic use, especially when radiation can be detected externally
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19
Q

Ideal properties of diagnostic radionuclides

A
  1. Gamma ray emission only
    • High abundance
    • Reduce radiation dose to patient
  2. For imaging studies, gamma energy 100-250 keV
    • High detection efficiency
    • No significant body attenuation
    • Easy to shield
  3. Physical half-life approx. 1.5 times duration of test
  4. Simple cheap and rapid production
    • Lack of radionuclidic impurities
    • High specific activity
    • Rapid production reduces operator dose
  5. Versatility chemistry- chemically bind it to lots of different molecules
20
Q

Ideal properties of diagnostic radionuclides

A
  1. Chemical quantity- No pharmacological effect
  2. Radiochemically pure- biodistribution profile
  3. Chemically stable- doesn’t break down in vivo
  4. Predictable biodistribution
21
Q

Technetium- 99m (Tc)

A
  • Metallic element atomic number 43
    • Hence 43 protons in the nucleus and 43 electrons
    • 20 different isotopes- all radioactive with half-lives of few seconds to millions of years
    • Existence predicted by Mendeleev’s periodic table
    • First artificially produced in 1937
22
Q

Technetium- 99m

A
  • The half-life of Technetium- 99m is 6 hours, gamma energy is 140 keV
  • Atomic number Mo is 42, Tc is 43, Ru 44
  • Principal gamma energies- 99Mo- 740 keV; 99Tcm- 140 keV
  • Ruthenium 99 is stable
  • Molybdenum and technetium have different chemical properties and can be separated
  • m= metastable state
23
Q

Source of Mo-99

A
  • From fission of U-235 in nuclear reactor
  • Bombard U-235 with thermal neutrons
  • Nucleus splits into 2 daughter nuceli
  • Not all nuclei split in same way
  • Large range of nuclides produced
  • Mo-99 can be separated relatively easily
  • Main site- S.Africa, Holland
  • None in UK
24
Q

Technetium Generator

A
  • Contains shielded glass column packed with alumnia
  • Chemical form of Mo is molybdate- MoO42-
  • Mo-99, as molybdate is strongly absorbed on to column
  • Decays to produce pertechnetate- TcO4-
  • Passage of saline through alumnia elutes pertechnetate
  • Sodium (99-Tc) pertechnetate is used for one day
  • MoO4- remains on alumina column and decats to produce more TcO4-
25
Q

What happens on a molybdenum column

A
  • Put in Mo99- this adherse to the aluminium column
  • Mo99- breaks down into Tc99
  • Saline is passed through the tube and flushes technecium out of the column
  • Leaving molybdenum behind
26
Q

Generator Elution

A
27
Q

Transient equilibrium on column

A
  • Molybdenum= 67 hr half-life
  • Time to re-establish equilibrium is 22.89
28
Q

Technetium level as fraction of maxium

A
29
Q

Choice of generator

A
  • Based on: Ease of operation; Efficiency and safety profile; Cost
  • Practical points
    • Must swab collection vial’s rubber bund
    • Should elute in a grade A environment
    • Make sure collection vial has reached atmospheric pressure before removal- try to prevent aerosol production
    • Require shielding to protect operator
30
Q

Radionuclidic purity/Identity

A
  • This is defined by the B.P. as
  • The radio, expressed as a percentage, of the radioactivity of the Radionuclide concerned to the total radioactivity of the source
  • E.g. with 99Tc Sodium pertechnetate, what percentage is 99-mTcand how much is 99-Tc and 99Mo impurities are there
31
Q

Radionuclidic purity/Identity

A
  • 99-Tc/ 99-Mo generator
    • Not done routinely
    • Can identify unknown isotopes (e.g. if have a spill)
    • Can be useful with unlicensed material
  • Methods
    • Molybdenum breakthrough test- if there is significant exposure after placing in sheild= molybdenum
    • Gamma spectroscopy
    • Measurement of energies emitted
    • Measurement of decayed sample
    • Determination of half-life
32
Q

Sodium (99-Tc) pertechnetate

A
  • Can be administered directly in that form
  • Most common indication is thyroid imaging
  • Why is pertechnetate taken up by thyroid
  • TcO4 has similar shape and size to iodine
    • TcO4 -tetrahedral- 4 x 10-23 cm3
    • Iodide - spherical- 4.2x10-23 cm3
  • Thyroid uptake
    • ~2% of TcO4
    • ~20% of iodide
33
Q

Sodium (99-Tc) pertechnetate

A
  • More commonly manipulated to produce Tc in different chemical form
    • Different chemistry= different biodistribution
    • Get information from different parts of body
    • TcO4- chemically stable, Tc has valency of +7
    • In order to make TcO4 react, need to alter valency state of Tc
    • Oxidation states of -1 to +7 are known
34
Q

Radiopharmaceutical Kit preparation

A
  • 99mTc can exist in valency states of +7 to -1 and form range of co-ordination complexes
  • It is eluted in most stable oxidation state (+7)
  • All 7 electrons are shared with 4 oxygens
  • Tc ion is surrounded by big O and ligand can’t get near
  • Tin Ions in kit are more attractive to oxygens, which leave Tc leaving it highly reactive
  • In this state can attach to ligand or may react with water to give Tc colloid
35
Q

Radiopharmaceutical production

A
36
Q

Modification of TcO4

A
  • Might still have some of TcO4 and Tc-colloid there are impurities- they are not useful for scan they just irradiate the body so must be kept to a minimum
  • Most vials are N rich- Not Oxygen because more oxygen will attach to Tc
37
Q

Preparation of Technetium radiopharmaceuticals

A
  • Simple technique- usually single addition of TcO4- to a kit- a freeze dried vial containing all required components
  • Stannous chloride most frequently used reducing agent
  • Kits commercially available products with product licences
  • Generally multidose containers
  • All manipulation performed aseptically
38
Q

Precautions

A
  • NEVER inject air into any technetium radiopharmaceutical vial
  • The oxygen in 0.1mL air can oxidise the stannou ion used in many commercial kits as a reducing agent
39
Q

Radiopharmaceutical kits

A
  • Contain all the required ingredients for preparation of Tc radiopharmaceuticals
    • Ligand, Sn++, buffers- pH affects oxidation state, stabilisers
  • Single, sterile freeze dried rubber capped vial
  • Vials contain nitrogen atmosphere
    • Prevent oxidation of Sn2+
  • Addition of TcO4 dissolves freeze dried powder and chemical reaction occurs
  • Some kits need boiling
40
Q

Ligand choice

A
  • Choice of ligand important- structure of Tc-ligand determines biodistribution
  • Compounds containing N,S,O and P atoms capable of sharing or donating electrons
  • Over 20 different Tc complexes in routine clinical use
  • Prepared daily as required in radiopharmacy department
  • Preparation kept as simpple as possible
    • Less handling- lower radiation exposure of staff
      • Less chance of microbial contamination
41
Q

Example: Tc-99m bone radiopharmaceuticals

A
  • Methylene diphosphonate (medronate, MDP)
  • P-C-P bonds resistant to phosphatase enzyme
  • Can be labelled with Tc-structure
  • Binds to hydroxyapatite Ca10(PO4)6(OH)2-imaging during bone growth- osteoblast
  • Greater the bone turnover, greater uptake
  • Can detect changes before change in bone density
42
Q

Quality control of radiopharmaceuticals

A
  • Radiochemical purity determination RCP is the % of the radionuclide that is present in the stated chemical form
  • Mostly assessed through chromatography
  • % of Tc-ligand should be >95% to pass
  • % of free TcO4- and reduced Tc <5%
43
Q

Quality control of radiopharmaceuticals

A
44
Q

Quality control of radiopharmaceuticals

A
  • Most assays rely on separation methods
  • Column chromatography- HPLC
    • Good separation but all activity may not be recovered from column
    • Expensive equipment; requires expertise to un
  • Planar chromatography- Use of stationary phase e.g. ITLC SG or filter paper + mobile phase
    • Separation not always as good, but all activity may be measured
45
Q

Quality of control of radiopharmaceuticals

Mobile phasesused

A
  • Butanone or acetone may be used to separate 99m TcO4 from mixture
  • Saline used to separated 99mTcO4 and 99mTc-ligand from 99mTc-colloid
  • Exceptions include 99mTc MAG3 which is more difficult to separate
46
Q

How will this affect the patient

A
  • Free TcO4- will be taken up in salivary glands, thyroid and stomach
    • Reduced Tc goes to liver and spleen- i.e. irradiation of unintended organs
  • Sub-diagnostic images
  • Repeat scan required- doubling radiation dose to the patient

PH3704- Pharmaceutical technology (22 decks)

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