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Radiochemistry and
Radiopharmaceuticals 1
Dr Benjamin H. Fraser
Nuclear Technologies for Health
Program Manager
ANSTO Human Health Research
Theme
Ionising Radiation
or +-
Alpha – High energy helium nucleus
Beta – High energy electron or positron
Gamma – High energy electromagnetic wave
Neutrons – High energy neutral particle
Penetrating power
Definition
Ionising radiation consists of particles or
electromagnetic waves that are energetic
enough to detach electrons from atoms or
molecules
n
Units of Ionising Radiation and Dose
SI units – The becqurel (Bq)
1 Bq = 1 disintegration per second
Historical Convention – The curie (Ci)
1 Ci = 37 billion disintegrations per second
1 Ci = 3.7x1010 Bq = 37 GBq
Absorbed dose units – The gray (Gy)
1 Gy = 1 J/Kg
6-10 Gy (fatal) = chemical energy of 20 mg of sugar
Dose equivalent units – The sievert (Sv)
1 Gy = 1 Sv (for gamma radiation, electrons and photons)
1 Gy = 20 Sv (for alpha particles)
1 Gy = 30 Sv (for neutrons)
6-10 Sv – acute radiation sickness and probable death
What is 1 disintegration?
What are Radiopharmaceuticals?
Radioisotope:
Positron emitter,
beta emitter, alpha
emitter, gamma
emitter.
“Pharmaceutical” or biological vector:
small molecule, peptide, protein,
antibody, nanoparticle, metal ion
Biological target: cell surface receptor, enzyme,
cell surface transporter, metal ions (Ca2+)
Two classes: Imaging and Therapy Radiopharmaceuticals
Chart of the Radionuclides
Chart of the Radionuclides
Neutron rich
- reactor produced
- β- emission
Neutron deficient
- particle accelerator produced
- β+ emission or electron capture
Fluorine-18
β+ emission
PET imaging
Chart of the Radionuclides
Iodine-131
Therapy &
SPECT
imaging
Lutetium-177
β- emission
Therapy
What are Radiopharmaceuticals?
Imaging Radiopharmaceuticals
Imaging radiopharmaceuticals are most often injected into the blood stream, allowed to circulate and
accumulate at “sites of interest” in the body. The emitted radiation (often gamma radiation) is detected
and translated into a 2D or 3D image. The relative uptake (as shown by the image) in different parts of
the body gives detailed physiological information which helps diagnose disease. Ideal imaging
radiopharmaceuticals are administered at very low doses and illicit no pharmacological response, and
induce no pharmacological side effects.
- Single-photon emission computed tomography (SPECT) imaging agents: Technetium-99m
- Positron Emission computed Tomography (PET) imaging agents: Fluorine-18
Therapy Radiopharmaceuticals
Therapy radiopharmaceuticals are most often injected into the blood stream, allowed to circulate and
accumulate at “sites of interest” in the body. The emitted radiation (alpha, beta or gamma) is mostly
absorbed by the local tissue at the site of accumulation. The target tissue is often malignant tumour cells
which are preferentially damaged and/or killed by the radiation. This preferential killing of malignant cells
over healthy cells produces a “therapeutic” benefit for the patient.
- Alpha emitting radiotherapy agents: Bismuth-212, Astatine-211
- Beta (electron) emitting radiotherapy agents: Iodine-131, Lutetium-177
- Auger electron radiotherapy agents: Iodine-125, indium-111, Technetium-99m
Radiotracers in action: FDG
What are Radiopharmaceuticals?
Exposure to Ionising Radiation
Australian Background Dose
• 1500 μSv per year
• 0.03 μSv per hour (sea level)
• 0.23 μSv per hour (La Paz, Bolivia, 3,900m)
Radiation Industry Worker Limits
• 20,000 μSv per year
• 12,000 μSv per year @ ANSTO
• 1-2 μSv per session
• No increased risk of cancer
Everyday Doses
• 5-10 μSv per single dental X-ray
• 8000 μSv per single FDG scan
• 13000 μSv per single X-ray CT abdomen scan
• 2200 μSv per year for flight crew
Reducing Radiation Dose
Distance
Dose received is proportional to the inverse square of distance
Dose α 1/distance2
Doubling the distance reduces the dose received by a factor of 4, tripling the distance reduces the dose by a factor of 9.
Administer the radiopharmaceutical with a technique that maximises the distance. Once administered, place the used
device (i.e syringe) in a location remote from where you are working (i.e. shielded lead bin).
Time
Dose received is directly proportional to time of exposure
Dose α Time
Doubling the time of exposure doubles the dose, tripling the time of exposure triples the dose.
Perform the administration of the radiopharmaceutical as quickly and safely as possible
Do not spend any more time than necessary in proximity to the radiopharmaceutical
Reducing Radiation Dose
Shielding
Personal protective equipment
(gloves, lead apron, shielded dispensing
area, shielded bin for disposal)
Gamma radiation
(PET, SPECT radiopharmaceuticals)
lead and other high Z materials
Beta and alpha radiation
(therapy radiopharmaceuticals)
paper and plastic
Technetium-99m
Radiopharmaceuticals - SPECT
The world’s most commonly used diagnostic medical radioisotope
40 million doses used world-wide annually
ANSTO produces 10,000 doses per week for Australian patients
Technetium-99m decays via gamma emission (88%) and internal conversion or
electron ejection (12%) with a half-life of six hours
Gamma emission is detected by mobile cameras and converted into an image
(SPECT imaging)
Imaging of brain, thyroid, lungs, liver, spleen, kidney, gall bladder, skeleton, blood
pool, bone.
Tc99m
43 Tc9943
141 keV gamma
6 hours
249 keV beta (-)
211,000 yearsRu99
44Ruthenium-99
(stable)
Single-Photon Emitted Computed
Tomography (SPECT)
SPECT image
Technetium-99m
Radiopharmaceuticals
Technical report serials no. 466
Technetium-99m Radiopharmaceuticals: Manufacture of kits
IAEA publications
