(PM3B) Radiotherapy & Nuclear Pharmacy Flashcards
What is a nuclide?
Species of an atom with a specific number of protons + neutrons in its nucleus
What is radioactivity?
Spontaneous transformation of an unstable nucleus
To a more stable nucleus
With release of ionising radiation
What is ionising radiation?
Radiation with enough energy to remove bound electrons when interacting with an atom
What are some types of radiation?
(1) Alpha – positively charged helium nuclei (2 protons + 2 neutrons)
(2) Beta - electrons
(3) X-rays – electromagnetic radiation
(4) Gamma – electromagnetic radiation
How are X-rays emitted?
When a heavy metal target is bombarded by energetic electrons
What is the penetrating power of alpha radiation?
Stopped by paper
What is the penetrating power of beta radiation?
Paper
Stopped by thin plates (made of wood/ aluminium)
What is the penetrating power of x-ray radiation?
Paper/ thin plates
Stopped by lead/ iron/ thick metal plates
What is the penetrating power of gamma radiation?
Paper/ thin plates
Stopped by lead/ iron/ thick metal plates
What is the penetrating power of neutron radiation?
Paper/ thin plates/ lead/ iron/ thick metal plates
Stopped by water/ concrete
What is the charge of alpha radiation?
Positive
What is the charge of beta radiation?
Negative
What is the charge of X-ray radiation?
Neutral
What is the charge of gamma radiation?
Neutral
What is the particle mass of alpha radiation?
Heavy particles
What is the particle mass of beta radiation?
Light particles
What is the particle mass of X-ray radiation?
No mass
What is the particle mass of gamma radiation?
No mass
What are some harmful effects of radiation?
Depends on exposure time/ penetration power/ energy of radiation
(1) Nausea
(2) Skin burns
(3) Hair loss
(4) Sterility
(5) Cancer
(6) Death
What are some useful applications of radiation?
(1) Cancer treatment
(2) Medical instrument sterilisation
(3) Finding leaks
(4) Dating archaeological remains
(5) Generating electricity
From which source is alpha radiation most damaging?
Internal source
From which source is beta radiation most damaging?
Internal source
From which source is x-ray radiation most damaging?
External source
From which source is gamma radiation most damaging?
External source
What is half-life?
Time it takes for activity/ amount of radioisotope to fall by 50%
Shorter half-life = more unstable
What is a long-life radiopharmaceutical?
Half-life >12 hrs
What is a short-life radiopharmaceutical?
Half-life <12hrs
What is the activity of a radioactive substance?
The number of nuclear transformations per unit of time
What is the unit of disintegration per second?
Becquerel – Bq
What is the unit for 3.7x10^10 disintegrations per second?
Curie – Ci
What is 1 millicurie?
1mCi = 10^-3 curie
What is 1 microcurie?
1µCi = 10^-6 curie
What is 1 megabecquerel?
1 MBq = 10^6 Bq
What is 1 kilobecquerel?
1 kBq = 10^3 Bq
What is the specific activity of a radioactive material?
Activity of particular radionuclide
per unit of mass of element/ compound
Usually expressed as activity per gram
What is radioactive concentration?
Of a solution
Activity of particular radionuclide in a unit volume
What is absorbed dose of radiation?
Energy deposited
per unit of mass of material
What is dose equivalency in radiation?
Accounting for variation in biological effectiveness of different radiations
Measured in sieverts (Sv)
What is dose equivalent?
Dose equivalent = Absorbed dose/ quality factor
What is the quality factor of alpha radiation?
20 Sv
What is the quality factor of gamma radiation?
1 Sv
What is the quality factor of beta radiation?
1 Sv
What radiation type is used diagnostically?
X-rays
What is radiopharmacy?
Manufacture + use of radioactive medicines
What are the categories of use for radiopharmaceutical?
(1) Diagnostic
(2) Therapeutic
What factors are important to consider when implementing therapeutic use of radiation?
(1) Specific targeting
(2) Clearance of radioactivity from non-target radiosensitive tissues
(3) Decay properties of radionuclide
What is the mechanism of action of radiation?
(1) Direct damage
- DNA single + double stranded breaks
(2) Indirect damage
- Hydrolysis of water
- Water reacts with components
- Single + double DNA breaks
- Breakage of disulfide bridges in proteins
What are some approaches of radiotherapy to treat cancer?
(1) External beam radiation
(2) Sealed source radiotherapy – brachytherapy
(3) Unsealed source therapy
What is external beam radiation?
Use of x-rays/ gamma rays
Higher energy than for diagnostic purposes
(1) Therapeutic: 1-25MeV (megaelectronvolts)
(2) Diagnostic: 20-150KeV (kiloelectronvolts)
Lower energy range used to treat skin cancer
Higher energy used to treat internal tumours
When is the lower range of energy use in external beam radiation?
Skin cancer treatment
When is the higher range of energy use in external beam radiation?
Internal tumours in cancer
What is sealed source radiotherapy (brachytherapy)?
Delivers radioisotopes sealed into capsules/ wires
Radiation can escape but radioisotope cannot move
e.g. iodine-125 or caesium-131
Used for cervical/ prostate/ breast/ oesophageal/ skin cancer
What types of cancer is brachytherapy (sealed source radiotherapy) used for?
Used for cervical/ prostate/ breast/ oesophageal/ skin cancer
What are the dose rates for sealed source radiotherapy (brachytherapy)?
Low dose: ≤2 Gy/h
Medium dose: 2-12 Gy/h
High dose: >12 Gy/h
Usually use low and high dose
What is low dose rate brachytherapy?
Permanent implantation of radioactive seeds at site of action
Administered over weeks/ months
e.g. iodine-125
Used to treat prostate cancer
What is high dose rate brachytherapy?
Temporary insertion of radioactive wires into site of action
Potential for combination with external beam radiotherapy
e.g. iridium-192
What is unsealed source radiotherapy?
Localised at specific targets
Targeting due to properties of chosen radiopharmaceutical, e.g. iodine in thyroid
Oral/ IV solution
e.g. iodine-131/ strontium-89/ radium-223
Alpha or beta emission usually required
How can radiotherapy achieve pain relief?
Treatment with strontium-89 chloride
Beta radiation source
Unsealed source radiotherapy
What is hyperthyroidism?
Excessive production of thyroid hormones
How is radiotherapy used to treat thyroid cancer?
Iodine accumulates in thyroid
Because iodine is needed to make thyroid hormone
e.g. iodine-131 sodium (beta radiation source) used
Oral – solution/ capsule
How are radiopharmaceuticals dispensed?
In units of activity, e.g. kBq/ MBq
Pharmacist is responsible for proper prescribed dose preparation
How are radiopharmaceuticals used for diagnostics?
Require gamma emission
NOT alpha/ beta emission
Administered IV
Radiation is detected externally using a gamma-camera
What is a gamma-camera?
Special scintillation detector
External radiation detection
What is positron emission tomography?
Observation of metabolic processes
Uses radiolabelled glucose, e.g. fludeoxyglucose
Gamma source of radiation
Identification of tumours – due to increased number of mitochondria in rapidly growing malignant masses
What is a renal isotope scan?
Used to test renal function
e.g. technetium-99
What are the stages of a renal isotope scan?
(1) IV injection of radionuclide
(2) Kidney tubules secrete radionuclide into urine
(3) Rate of radionuclide removal vs time = renogram
What is a renogram?
Results of renal isotope scan
Rate of radionuclide accumulation/ removal vs time
What is technetium?
Lightest chemical element with no stable isotope
Most commonly used radioisotope in medicine
Emits gamma radiation only
Half-life = 6hrs
How is technetium prepared for radiotherapy?
On site
In water
Injected into patient
What is cardiolite treatment?
Most important myocardial imaging method
Non-invasive
What is the most important myocardial imaging method?
Cardiolite treatment
What is technetium-aerosol used for?
Lung ventilation imaging
What is technetium-albumin used for?
Cardiac function imaging
What is technetium-exametazime used for?
Brain imaging
What is technetium-medronate used for?
Bone imaging
What is technetium-succimer used for?
Kidney imaging
What are some safety considerations for radiotherapy treatment?
(1) Shielding – shielding from rays
(2) Distance – radiation dose is inversely proportional to square of the distance
(3) Time – minimise time spent handling radioactive source