Health Physics

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Slide 17

Radiation Therapy Brachytherapy

Uterus

Cervix

Prostate

Intraocular

Skin

Thyroid

Bone

Brachytherapy is used to treat the following cancers:

Slide 18

Tracers

There are many uses of ionising radiation based on the fact that it is easy to detect. In such applications, the radioactive material is used in the form of a tracer.

In nuclear medicine, a tracer is a radioactive substance which is taken into the body either, as an injection, or as a drink. Such a substance is normally a gamma emitter which is detected and monitored.

This gives an indication of any problems that may be present in body organs or tissues by how much, or how little, of the substance has been absorbed.

Slide 19

Nuclear Medicine Tracers

A drug which is chosen for the particular organ that is being studied.

A radioactive substance which is a gamma emitter.

It is important to be able to study internal organs, or tissues, without the need for surgery. In such cases, radioactive tracers can be injected into the body so such studies can take place. The path of these tracers can be detected using a gamma camera because of their radioactivity.

Such tracers consist of two parts:

Slide 20

Tracers Used in Nuclear Medicine

Slide 21

Factors Which Affect the Choice of Tracer

They will concentrate in the organ, or tissue, which is to be examined.

They will lose their radioactivity (short t).

They emit gamma rays which will be detected outside the body.

Such tracers are chosen so that:

Slide 22

Factors Which Affect the Choice of Tracer

Gamma rays are chosen since alpha and beta particles would be absorbed by tissues and not be detected outside the body.

Technitium-99m is most widely used because it has a half-life of 6 hours.

Slide 23

Why is a half-life of 6 hours important?

A shorter half-life would not allow sufficient measurements or images to be obtained.

A longer half-life would increase the amount of radiation the body organs or tissues receive.

A half-life of 6 hours is important because:

Slide 24

The Gamma Camera

The tracer is injected into the patient. The radiation emitted from the patient is detected using a gamma camera.