8. Nuclear Medicine

Question 1

Radiotherapy

Answer 1

Ionising radiation is used to kill cancer cells

Can be both internal or external

Question 2

Internal Radiotherapy

Answer 2

An implant is placed close to the tumour inside the body.

Question 3

External Radiotherapy

Answer 3

High-energy rays are directed from outside the body into the tumour.

Question 4

Ionising radiation

Answer 4

Ionising radiation is a type of particle or electromagnetic wave that carries enough energy to remove electrons from an atom or a molecule.

Rays and particles that ionise atoms and molecules:
Gamma rays
X-rays
The higher end of UV rays.
Alpha particles
beta minus particles

Question 5

Damage to DNA

Answer 5

Ionising radiation damages DNA either directly or indirectly

Direct damage - the radiation collides directly with the DNA molecule

Indirect damage - a free radical produced by the ionising ration reacts with the DNA

Question 6

Side effects of radiotherapy

Answer 6

Radiotherapy also damages healthy cells and tissues near the area being treated.

Fatigue, Nausea, Hair-loss, Sterility & Skin reactions.

Question 7

Targeted alpha Therapy (TAT)

Answer 7

Cancer treatment that uses radioactive isotopes that undergo ALPHA DECAY

• Selectivley targets cancer cells (no damage to good)

Treats: melanoma, breast, rectal, ovarian, prostate and pancreatic cancers.

Question 8

Targeted alpha Therapy => Means of action

Answer 8

1) Lead 212 => Bismuth 212 + beta minus particle
2) Lead 212 => Thallium 208 + alpha particle

1) An alpha emitter attaches to an antibody through the use of a chelator
2) because it’s an antibody it selectivley targets cells.

Question 9

Alpha Particle

Answer 9

HIGHLY ionising
- effective at killing cancer cells

SHORT range
- minimises damage done to healthy tissue

Question 10

Boron neutron capture therapy (BNCT)

Answer 10

Treat neck and head cancers
The tumour is irradiated with low energy neutrons which cause it to emit high energy alpha particles that kill the cancer cells.

Effectiveness depends on the uptake of B-10 by the cancer cells. If only small amounts are uptaken by healthy cells then damage is minimized

Question 11

Boron neutron capture therapy => Means of action

Answer 11

The patient is injected with the non-radioactive isotope Boron-10 which concentrates in the tumour.

1) Boron-10 absorbs 1 neutron => Boron-11

(Boron-11 is an intermediate, that is unstable)

2) Boron-11 => Lithium-7 + alpha particle

AKA: (Absorbs neutron -> intermediate -> alpha decay)

Question 12

Isotopes used in radiotherapy and nuclear medicine

Answer 12

Tc-99m
Lu-177
Y-90
I-131
Pb-212 (TAT)

Question 13

Targeted radionuclide therapy with Yttrium-90
(beta minus decay)

Answer 13

Treat tumors in liver
1) Thousands of tiny beads are embedded with Y-90 and are delivered to the tumour in the liver
2) The blood vessels that sustain the tumour are smaller in size than those that feed healthy tissue, therefore the beads get stuck in the smaller blood vessel and target only the tumour / cancer cells.

Question 14

Radioactive tracing with Technetium-99m

Answer 14

Tc-99m most common used radioactive tracer
- 6 hour half-life
- low energy emission level (just enough for gamma cameras to detect in body)
- Different forms of the isotope can travel to different organs and parts of the body

Question 15

Thyroid treatments with Iodine-131

Answer 15

When in body it is absorbed by the thyroid gland and begins destroying the gland cells
(undergo beta minus decay)

Gamma radiation is also emitted hence patients should avoid having prolonged close contact with others for about 3-4 days after treatment.

Question 16

Radioactive Half-Life (T-1/2)

Answer 16

Quantity of substance remaining = initial quantity of substance ( 1/2 ) ^ time elapsed / half-life

Question 17

Half-Life

Answer 17

The half life of a radioisotope is the time taken for half of all the radioactive nuclei in a sample to undergo radioactive decay.