Radiopharmacy (Cheng) Flashcards
What are radiopharmaceutcials?
a dosage form consisting of radioactive compounds used for wither the diagnosis or therapeutic treatment of human diseases
What gives an unstable nucleus?
change in the number of neutrons (N)
What does Z stand for?
atomic number
Z > 83
radioactive
What happens when radionuclides decay?
they emit particles/energy in the form of stable nuclide
- alpha, beta, positron, neutrons, gamma
Where is alpha decay seen?
heavy metals (uranium)
What is alpha emission? (alpha, 4He nucleus)
2+ charge of high energy and limitied penetration range
-> nucleus has too many protons
What is beta decay? (beta-)
various energy
random motion
negative charge
-> nucleus is neutron rich
What are gamma rays/gamma decay? (y)
when nucleus energy is too high
no mass loss
photon energy
high penetration range
isomeric transition - exicted nucleus emits gamma rays
-> if isomeric state is long lasting then it’s meta stable (m)
What is positron decay? (beta+)
positive charge (loss is a proton) various energy random motion proton rich
What is neutron emission? (n)
during fusion of heavy metals
no charge loss
loss of mass
What is the disintegrating rate?
average number of nuclei that disintegrate during a period of time
What is physical half life?
time required to reduce the initial disintegrating rate or activity to one half (outside the body)
tp
What is biological half life?
time needed for half of the radiopharmaceutical or radionuclide to disappear from the biological system (inside body)
tb
effective half life (te) formula
1/te = 1/tb + 1/tp
dps
disintegrations per second
units for radioactivity
curies (Ci)
Bacquerel (Bq) - SI unit
How to convert Curies to Bacquerel
1 Bq = 2.7 x 10^-11 Ci
How to produce radionuclides?
nuclear reactor (neutrons) OR cyclotron (charged particles)
What does a nuclear reactor do?
produces neutron rich radionuclides
-> fission/reaction of 235U or 239Pu
What does a cyclotron do?
produces proton rich radionuclides
properties of reactor/cyclotron
expensive
produce radionuclides have long half life
What is used for radiopharmacy in hospitals?
generator system
- portable and reusable system
- lead shiels
- radionuclides have short half life
- cheaper
What is the most widely used imaging radionuclide?
99Mo to produce 99mTc
-> molybdenum and technetium
How is 99Mo produced?
from 235U fission
uranium
solid and solvent phase in 99Mo 99mTc generator
solid - alumina column
solvent - 0.9% saline
properties of 99Mo 99mTc generator
sterile and pyrogen free
physiological pH and isotonic
What element is Tc?
technetium
dosage forms of radiopharmaceuticals
solution suspension capsule gas -> in a lead container
forms of radiopharmaceuticals
ions
molecules
complexes
What is idrect labeling?
- tagging radioisotope with biological molecules
- non-specific binding to antibodies, RBC etc
How to label 99mTc with chelate?
- the oxidation state of Tc needs to be lower (1+ - 5+)
- use reducing agents like stannous chloride (SnCl2) in acid
- > lowers Tc oxidation state
- use a chelating agent
- > donates a lp of e- to Tc to form a stable complex by formation of a covalent bond
How to lower the oxidation state of 99mTc?
use a reducing agent in acid
-> SnCl2 (stannous chloride)
How to stabilise the bonds in 99mTc?
using a chelating agent
- it donates a lp of electrons to Tc
- coordinates a covalent bond to stabilise 99mTc
2 structures of 99mTc labelled complexes
Tc-HMPAO
Tc-sestamibi
What do commercial 99mTc labelling kits contain?
NO RADIOISOTOPE
- reducing agent (SnCl2)
- chelating agent
- antimicrobial
- antioxidant
- buffers (acid/base)
- solution or lyophilised powder
- vials for reconstitution/reaction
What does the antimicrobial do in a labelling kit and an example?
benzyl alcohol
maintains sterility of the kit
What do antioxidants do and example of one in labelling kit?
sodium bisulfite
avoid re-oxidation of reduced Tc if Sn delpetes
What do buffers do in labelling kit?
maintain pH of the kit
2 types of quality control tests for radiopharmaceuticals
- physiochemical tests
2. biological tests
What do physiochemical tests do in quality control of radiopharmaceuticals?
- radioactivity and specific radioactivity
- radionuclidic species and radionuclidic purity
- chemical purity for radiopharmaceuticals and radiochemical purity
- particle size
- pH
What do biological tests do in quality control?
sterility and pyrogen tests
What is radionuclidic purity?
fraction of total radioactivity in form of the desired radionuclide present in a radiopharmaceutical
Where can impurities come from?
extraneous nuclear reaction
isotope impurities in target materials
impurity in 99mTc
99Mo
What detects impurities in radionuclidic?
gamma spectrometry
What is radiochemical purity?
fraction of total radioactivity in desired chemical form in a radiopharmaceutical
What can cause radiochemical impurity?
decomopsition action of solvent, heat, light and radiolysis
What detects radiochemical impurities?
chromatographic techniques
examples of radiochemical impurities
free 99mTcO4-
OR
hydrolysed 99mTcO2 in 99mTc labelled albumin
What does specific activity mean?
total amount of radioactivity per unit mass of a radionuclide or labelled compounds
What does specific activity account for?
radioactive concentrations and chemical substance concentrations
What does specific activity change with?
date and time
What is radiolysis?
decomposition of radiopharmaceutical by radiation
-> 2 types - auto-radiolysis and indirect radiolysis
What is auto-radiolysis?
absorption of radiation leads to free radical formation
What is indirect radiolysis?
production of peroxide or radical from decomposition of water
What does stability of radiolaballed product depend on?
specific activity
energy of emitted radiation
half life
Why can positrons be given at a higher dose and higher radiation dosing?
they have a very short half life
How to image the thyroid gland?
- radioactive iodine given as sodium iodide 131I or 123I capsule given orally
- uptake is monitored, gamma detector used
- absorbed into thyroid gland
- 10-35% after 24hrs
- hot spot = hyperthyroidism
- cold spot = carcinoma
What is used for thyroid imaging?
sodium iodine-123 or I-131
alternative for sodium iodine for thyroid imaging
99mTc pertechnetate preparation
What radiopharmaceutcials are used as therapeutic agents?
- particle emitters - alpha and beta ionisation energy
- direct/indirect free radical induction
- permanent damage to DNA
- induces cellular apoptosis
How do alpha/beta particles cause permanent damage to DNA?
via strand clevage and base pair mutations
How to treat bone matastasis with radiopharmaceuticals?
- 32 P-sodium orthophosphate IV (radioactive sodium phosphate injection)
- deposits in the bone
What radiopharmaceutical is used to treat hyperthyroidism?
NaI (131 I) - sodium iodine 131
emits beta- and gamma rays/particles
larger gland = larger dose
