Radiopharmacy

Question 1

Radiopharmaceutical

Answer 1

A chemical contains a radioactive isotope for diagnosis, mitigation, or treatment of disease

Question 2

Organ specificity

Answer 2

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

Question 3

Single photon emission computerized topography

Answer 3

Motion picture reconstructed from a series of topographic images
Rotates around the patient

Question 4

Types of radioactive decay

Answer 4

A: two protons and two neutrons leave (penetrates the least)
B: high energy electron leaves
Y: high energy electromagnetic photon leaves (penetrates the most)

Question 5

Activity

Answer 5

Disintegrations per second

Question 6

Bq

Answer 6

SI unit of activity corresponding to one disintegration/sec

Question 7

Curie

Answer 7

Historical unit of activity corresponding to 1 g of pure Ra
Equivalent to 3.7 x10^10 Bq

Question 8

Radiopharmaceutical doses

Answer 8

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

Question 9

Specific activity

Answer 9

Refers to radioactivity per unit weight

Question 10

Absorbed dose

Answer 10

Energy deposition in matter

Question 11

Gray

Answer 11

SI unit corresponding to deposition of 1 joule per kilogram of material

Question 12

Radiation absorbed dose

Answer 12

Historical unit corresponding to deposition of 100 ergs per gram of material
1 rad= 100 erg/g=0.01 Gy

Question 13

Dose equivalent

Answer 13

Biological measure of damage

Question 14

Sievert

Answer 14

SI unit: amount of radiation roughly equivalent in biological effectiveness to one gray of gamma radiation
1 Sv= QF x 1Gy

Question 15

Radiation equivalent man

Answer 15

Historical unit
1 rem= QF x 1 rad
1 rem = 0.01 Sv

Question 16

Dose equivalent

Answer 16

Biological measure of damage

Question 17

Quality factor

Answer 17

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

Question 18

Factors of radiation damage

Answer 18

Types of radiation
Dose
Amount of exposure (time, distance)

Question 19

Is radiation dangerous

Answer 19

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

Question 20

Radiation sickness

Answer 20

> 100 rem: intestinal lining damage
300 rem: immune system damage
400 rem: 50% of people die within 60 days mostly due to infection

Question 21

Radiation in mREM/yr on average

Answer 21

360 in non smokers
510 in smokers

Question 22

Sources of radiation exposure

Answer 22

External: cosmic rays, radioactive ores, radon gas, med X-rays
Internal: radioactive material, smoking

Question 23

Radiation dose

Answer 23

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?

Question 24

Pregnancy

Answer 24

Pregnancy may preclude nuclear medicine
Yes—Radioiodine crosses the placenta
No—A ventilation-perfusion scintigraphy procedure to detect PE

Question 25

Should women suspend breast feeding

Answer 25

Depends on the t1/2 of the radionuclide and degree it is secreted in milk Common to stop in the US

Question 26

Properties of an ideal diagnostic radiopharmaceutical

Answer 26

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

Question 27

Properties of an ideal therapeutic radiopharmaceutical

Answer 27

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

Question 28

Effective half life

Answer 28

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

Question 29

Cases of effective dose

Answer 29

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)

Question 30

Tc-99m

Answer 30

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

Question 31

Tc-99m chelate

Answer 31

Capable of binding radiometal cations Metal tightly bound in the center of octahedral structure Hexa-coordinated 6 binding sites consisting of O, N, P

Question 32

Bone scans

Answer 32

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

Question 33

Liver imaging

Answer 33

Uses Tc-99m sulfur colloid and Tc-99m micro-aggregated albumin to target kupffer cells

Question 34

Myocardial scanning

Answer 34

Tc-99m I-123-iodine-9-hexadecanoic acid TI-201

Question 35

Tumor imaging

Answer 35

Tc99m-MDP bone scans I-123 thyroid scans Tc-99m sulfur colloid liver scans Ga-67 accumulates preferentially at tumors

Question 36

Lung perfusion scans

Answer 36

Detect PEs Tc-99m macro aggregated albumin Ventilation scan using radioactive gas Xe-133

Question 37

Brain blood-flow studies (dynamic)

Answer 37

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

Question 38

Blood pool agents (dynamic)

Answer 38

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

Question 39

Mechanisms of localization of radiopharmaceutical

Answer 39

Active transport Phagocytosis Capillary blockade Cell sequestration Simple/exchange diffusion Compartmentalism localization Chemisorption Antigen/antibody reaction Receptor-binding