Radiopharmacy Flashcards
Radiopharmaceutical
A chemical contains a radioactive isotope for diagnosis, mitigation, or treatment of disease
Organ specificity
A radiopharmaceutical should have the capacity to localize in the target site under study with a high target-to-non-target ratio for optimum visualization and sufficient affinity to use the lowest dose possible
Single photon emission computerized topography
Motion picture reconstructed from a series of topographic images
Rotates around the patient
Types of radioactive decay
A: two protons and two neutrons leave (penetrates the least)
B: high energy electron leaves
Y: high energy electromagnetic photon leaves (penetrates the most)
Activity
Disintegrations per second
Bq
SI unit of activity corresponding to one disintegration/sec
Curie
Historical unit of activity corresponding to 1 g of pure Ra
Equivalent to 3.7 x10^10 Bq
Radiopharmaceutical doses
Are administered as tracer doses for diagnostic purposes rather than at doses to elicit a pharmacological response
Dispensed in units of activity
Amount must be sufficient to allow for decay before administration
Specific activity
Refers to radioactivity per unit weight
Absorbed dose
Energy deposition in matter
Gray
SI unit corresponding to deposition of 1 joule per kilogram of material
Radiation absorbed dose
Historical unit corresponding to deposition of 100 ergs per gram of material
1 rad= 100 erg/g=0.01 Gy
Dose equivalent
Biological measure of damage
Sievert
SI unit: amount of radiation roughly equivalent in biological effectiveness to one gray of gamma radiation
1 Sv= QF x 1Gy
Radiation equivalent man
Historical unit
1 rem= QF x 1 rad
1 rem = 0.01 Sv
Dose equivalent
Biological measure of damage
Quality factor
Effect of radiation on humans depends on type of radiation
QF is used to weigh radiation according to harmfulness in tissue
Range: 1-20 neutrons
QF=20 for alpha particles
Factors of radiation damage
Types of radiation
Dose
Amount of exposure (time, distance)
Is radiation dangerous
Releases free radicals
After sulfhydryl groups on proteins (oxidation)
Direct action on DNA (mutagenicity and carcinogenicity)
Radiation sickness
Risk of cancer 0.04% per rem
Radiation sickness
> 100 rem: intestinal lining damage
300 rem: immune system damage
400 rem: 50% of people die within 60 days mostly due to infection
Radiation in mREM/yr on average
360 in non smokers
510 in smokers
Sources of radiation exposure
External: cosmic rays, radioactive ores, radon gas, med X-rays
Internal: radioactive material, smoking
Radiation dose
Type and energy of radiation
Amount of radionuclide
Radionuclide distribution in the body
Relative size and sensitivity of tissues
Physical t1/2
Biological t1/2
Effective t1/2?
Pregnancy
Pregnancy may preclude nuclear medicine
Yes—Radioiodine crosses the placenta
No—A ventilation-perfusion scintigraphy procedure to detect PE
Should women suspend breast feeding
Depends on the t1/2 of the radionuclide and degree it is secreted in milk
Common to stop in the US
Properties of an ideal diagnostic radiopharmaceutical
Pure gamma emitter
100 < gamma energy < 250 KeV
Effective half-life = 1.5 X test duration
High target:nontarget ratio
Minimal radiation dose to patient and nuclear medicine personal
Patient safety
Chemical reactivity
Inexpensive, readily available radiopharmaceutical
Simple preparation and quality control if manufactured in house
Properties of an ideal therapeutic radiopharmaceutical
Pure beta minus emitter
Medium/high energy (> 1 MeV)
Effective half-life = Moderately long, e.g. days
High target:nontarget ratio
Minimal radiation dose to patient and nuclear medicine personal
Patient safety
Chemical reactivity
Inexpensive, readily available radiopharmaceutical
Simple preparation and quality control if manufactured in house
Effective half life
Good compromise: minimize radiation dose to patient and maximize it to have good counting statistics and image quality
1/t(effective)=1/t(biological) + 1/t(physical)
Usually measured in hours or days
Cases of effective dose
T(biological) is very long compared to t (physical) e.g Tc-99m sulfur colloid in liver
T(physical) is very long compared to t(biological)
Tc-99m
Most widely acceptable radionuclide for diagnostics
stable as TcO4 with valence of +7
TcO4 injected IV to label RBCs and other molecules for IV and reduced valence to +4
Oxygen introduced reduces Tc and hydrolyzes Sn
Tc-99m chelate
Capable of binding radiometal cations
Metal tightly bound in the center of octahedral structure
Hexa-coordinated 6 binding sites consisting of O, N, P
Bone scans
Very accurate at depicting a local increase in bone metabolism
Ca-45, Sr-85, and F-18 localize in bone lesions by ion-exchange at the surface of bone
Tc-99m MDP is also used
Bone tumors, fractures, Paget’s disease, and infection
Sr-89 is a beta-emitter and used for palliative of bone pain
Liver imaging
Uses Tc-99m sulfur colloid and Tc-99m micro-aggregated albumin to target kupffer cells
Myocardial scanning
Tc-99m
I-123-iodine-9-hexadecanoic acid
TI-201
Tumor imaging
Tc99m-MDP bone scans
I-123 thyroid scans
Tc-99m sulfur colloid liver scans
Ga-67 accumulates preferentially at tumors
Lung perfusion scans
Detect PEs
Tc-99m macro aggregated albumin
Ventilation scan using radioactive gas Xe-133
Brain blood-flow studies (dynamic)
Most common is a stroke
Tc-99m penetate
TcO4 distributes rapidly in ECF and brain
TcO4 used to determine brain death
When blood flow is in blood vessels outside the skull and no blood flow in the brain, cerebral death is said to have occurred
Blood pool agents (dynamic)
Tc-99m cells act as a tracer
Complications: drugs used to fight cancer affect heart function, ejection fracture management is used to assess the cardiotoxicity of doxorubicin
Most commonly used to measure heart failure
Mechanisms of localization of radiopharmaceutical
Active transport
Phagocytosis
Capillary blockade
Cell sequestration
Simple/exchange diffusion
Compartmentalism localization
Chemisorption
Antigen/antibody reaction
Receptor-binding
