Radiopharma

Question 1

What are the properties for radiopharmaceuticals?

Answer 1

Must be chemically pure, non-toxic, needs to have a short half life (reduce radiation dose & do enough damage to affected area)

Question 2

What is radio nuclidic purity

Answer 2

The radio nuclidic purity is defined as the fraction of the total radioactivity in the sample that is in the form of the required radionuclide

Question 3

What is the specific activity?

Answer 3

The specific activity determines the mass of a compound that is introduced for a given dose.
The mass should be low; thus specific activity should be high

Question 4

What is the physical half life

Answer 4

Physical half-life should be within seconds to days - must consider patient dose risk, and sufficient time for dose to prepare

Question 5

What is the ideal emission

Answer 5

Gamma = energy of 50 – 600 KeV are suitable, lower
energies will not get transmitted through the body

Question 6

What are the benefits of commercial generators?

Answer 6

Sterilised, automated, and large size, and impurity levels are low

Question 7

What is a disadvantage of commercial generators?

Answer 7

99Mo “breakthrough” which
is partial elution of the 99Mo parent.
* The amount of breakthrough needs to be
kept to a minimum for patient safety
reasons

Question 8

Describe the features of fission using molybdenum

Answer 8

Has a higher specific activity
* The amount of alumina required is
determined by the amount of
stable carrier

• Small volumes of saline required
  for elution, which is great for bolus
  injections

Question 9

What do dry generators have

Answer 9

Modern generators, typically “dry cell” construction using an evacuated vial to draw saline from a second vial through the ion- exchange column.

Question 10

What is a radionuclide generator?

Answer 10

A radionuclide generator is a device containing a radionuclide that decays to form the required daughter product

Question 11

How is the daughter nuclide separated in radionuclide generator?

Answer 11

The daughter can be separated by a physical process
– gaseous daughter
– solubility

Question 12

What are the characteristics of radiation from cyclotrons?

Answer 12

Cyclotron products have high photon/particle
emission ratios obtained in EC decay and Beta plus

Question 13

Difference between cyclotrons and nuclear reactor

Answer 13

Cyclotrons produce smaller quantities of radionuclides than nuclear reactors, thus are more expensive to operate

Question 14

In cyclotrons, the products are carrier free because

Answer 14

Addition of positive ions changes the atomic
number, thus products are usually carrier free
and have high specific activity

Question 15

Why does it undergo beta plus emission (cyclotron radiation)?

Answer 15

+ve charge is given to the nucleus, therefore
the product lies below the line of stability and
tend to decay by EC or Beta Plus

Question 16

Why are beta plus used for PET scans?

Answer 16

Beta plus are used for PET studies. Most have short
T1/2 values - need to have ready access to
cyclotron

Question 17

Explain how a cyclotron works with negative ions

Answer 17

When the –ve charged particles reach the
outermost orbit, they are passed through a thin
carbon foil which strips off the electrons creating +ve ions. The interaction of the magnetic field with the
+ve ion bends towards the target.

Question 18

Can 2 beams be extracted in the same time in cyclotron? (Yes)

Answer 18

Two beams can be extracted at the same time,
by positioning a carbon stripping foil part way
into the path of the beam, so that only a portion
of the beam is extracted

Question 19

Explain the cyclotron design

Answer 19

1.Uniform magnetic field
makes the particles orbit
2. Electric field keeps speeding them up
3. As they speed, orbital radius increases
4. They shoot out of the cyclotron at high speeds

Question 20

What does the e field do every half orbit?

Answer 20

Direction of the e-field changes every half orbit to keep particles accelerating across the gap

Question 21

Explain the operation of the cyclotron

Answer 21

1. Particles are generated in bursts by the ion source
2. High frequency AC voltage is applied across the dees.
3. particles are injected into the gap and accelerated
   towards one of the dees, the particles follow a circular path as they are in a magnetic field
4. particles are accelerated across the gap and continue on a circular path in the opposite direction; with the particles gaining energy each time they cross the gap
5. When the particles reach the maximum radius, they may be directed onto a target placed
   directly in the beam path, or may be extracted from the cyclotron and deflected by a negatively
   charged plate onto an external target (most common)

Question 22

Explain briefly (n,gamma) neutron activation.

Answer 22

A target nucleus captures a neutron and is converted into a product nucleus; this is in an excited state. The nucleus immediately
undergoes de-excitation (prompt decay) to the ground state by emitting
a gamma ray.

Question 23

In neutron gamma activation, the target and product are ______

Answer 23

The target and product represent
different isotopes of the same chemical
element

Question 24

What is neutron activation

Answer 24

When neutrons strike a target, some of the neutrons are captured by nuclei of the
target atom - either releasing a gamma ray or a proton

Question 25

What are the characteristics of fission radionuclides?

Answer 25

Fission products may be carrier free: Radionuclides
can be produced with high specific activity
- Lack of specificity
- Fission products always have an excess of neutrons hence undergo decay by beta minus emissions
until a stable nuclide is reached
Gamma decay typically follows as daughter nucleus
reaches stable state

Question 26

What are the fission products produced?

Answer 26

The fission process produces medically important radionuclides (131I and 99Mo) directly as fission products
* Fission of 235U leads to one fragment with a mass
number in the range 85 to 105 and another
fragment with a mass number in the range 130 to
150

Question 27

What is the purpose of coolant

Answer 27

To remove heat from the nuclear reactor core and transfer it to electrical generators and the environment.

Question 28

What is the purpose of the control rods

Answer 28

• Strong neutron absorbers
• Used to expose or shield the fuel cells
• Fuel cells and control rods are carefully positioned to control the chain reaction
• If removed, there could be a potential meltdown (e.g. Chernobyl)
• Insertion of additional control rods results in
  excessive absorption of neutrons and terminates the chain reaction (shut down)

Question 29

What is the role of moderator

Answer 29

• Slows down the energetic fission neutrons
• Slow (thermal) neutrons are more efficient initiators of additional fission events
• Uses “heavy water” (D2O) or graphite

Question 29

What is the purpose of fuel rods?

Answer 29

Fuel Cells
– Contain the fissionable material (generally U-235)

Question 29

Why is 235 U fissile?

Answer 29

Most important reaction:
235U + n → 236U* promptly undergoes fission releasing additional neutrons

– This means 235U is fissile. Results in a controlled, self-sustaining nuclear chain reaction

Question 30

What does carrier-free mean

Answer 30

A preparation of a radioactive isotope which is ‘free’ from stable isotopes of the element in question.
No stable isotope present
- Has the highest specific activity
- Fission products (once separated) provide highest carrier free product

Question 31

Name all the artificial radioisotopes

Answer 31

Reactor produced: Fission Particles & Neutron Activation
Accelerator Produced: Cyclotron
Radionuclide generators:
99Mo–99mTc generator