Medical Physics and Medical Physics and RadioactivityRadioactivity

RadioactivityRadioactivity

particleElectromagnetic wave

Unstable nucleus

Atoms which emit electromagnetic radiation or a particle by the spontaneous transformation of their nucleus are called radioactive.

Types of radiation

• Beta Particle (β)

• Gamma Ray (γ)

-

• Alpha Particle (α)

Uranite – a rock which contains uranium

Is radiation harmful?

• High energy radiation can damage DNA.• This could cause…

• Cancer• Inflammation• Cell death• Damage to genes can lead to mutations in offspring

• Cells are more sensitive to radiation during cell division than at other times.

• Cells which divide frequently (e.g. the gut walls) are more sensitivethan those which rarely divide (e.g nervous tissue).

Detection and MeasurementDetection and Measurement

Radiation detector

Each particle or gamma ray is seen as a deflection on the meterneedle and is heard as a click

The detector is responding to the radiation being emitted from the uranium ore

Nuclear Medicine

• Radioactive tracers can be used to see how well organs in your body are working or to find areas of disease.

e.g. radioisotopes of iodine or technetium.

• Often these are mixed with a drug that collects in a particular organ in the body.

• If we then inject the drug into the body, then by detectingthe radiation, we can examine that organ.

Labelling chemicals with the radioactive isotopes

Preparing the tracer

Lead

The tracer is injected into the patient

Gamma Camera

A gamma camera detects the radiation coming from the patient and produces an image of where the radioactivity is in the body.

The gamma camera displays the position of each gamma raythat it detects.

This is a bone scan made using technetium-99m.

Can you see where the patient was injected?

Lung scan using Krypton-81m gas

Lung scan using Krypton-81m gasventilation perfusion

A blood clot in the right lung is preventing blood from reaching the lower lobe of the right lung, although the ventilation imageshows that air is filling that region.

Which kidney is not working properly ?

• The right one,

How can you tell?

Computer software enables us to look at the kidney from all directions

(Positron Emission Tomography)

PETPET

CyclotronUsed to make radionuclides for PET imaging

The heart shows up clearly and the kidneys can be seen.

The brightest area shows that there is cancer in a rib.

heart

kidney

tumour

Combined PET/CT

RadiotherapyRadiotherapy

Radiotherapy• Gamma rays can kill cancer cells, but are

also dangerous to healthy cells

• We need to target the gamma rays to the cancer very precisely so that the radiation dose to healthy tissue is kept to a minimum.

• In particular we need to avoid any nearby organs such as eyes or spinal cord.

Gamma Knife

The radiation has to be precisely targeted.

Metal windows restrict the gamma ray beam size

This is the Gamma Knife in position.

A polystyrene model shows the position

that the patients head would occupy.

A patient’s eye view

Planning the treatmentA medical physicist decides how to target the gamma rays to destroy

the tumour and minimise damage to other tissue

Summary• Radiation can be dangerous so its use is carefully

controlled

• In medicine, radioactive materials can be used in both diagnosis and treatment.

• Medical Physicists provide expert guidance and ensure that the radiation is controlled, measured and deliveredto the benefit of the patient.

Acknowledgements

• Thanks to Emily Cook, Jeff Jones, The Nuclear Medicine Department of The Royal Free Hospital, London, and The Cromwell Gamma Knife Centre, London for providing images

• This lesson was developed by Adam Gibson, Jeff Jones, David Sang, Angela Newing, Nicola Hannam and Emily Cook

• We have attempted to obtain permission and acknowledge the contributor of every image. If we have inadvertently used images in error, please contact us.