Download Medical Physics and Radioactivity

Medical Physics and
Radioactivity
Radioactivity
Unstable nucleus
Electromagnetic wave
particle
Atoms which emit electromagnetic radiation or a particle by the
spontaneous transformation of their nucleus are called radioactive.
Types of radiation
• Alpha Particle (α)
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• Beta Particle (β)
• Gamma Ray (γ)
Uranite – a rock which contains uranium
Is radiation harmful?
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High energy radiation can damage DNA.
This could cause…
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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 sensitive
than those which rarely divide (e.g nervous tissue).
Detection and Measurement
Radiation detector
Each particle or gamma ray is seen as a deflection on the meter
needle and is heard as a click
The detector is responding to the radiation being
emitted from the uranium ore
Nuclear Medicine
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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.
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Often these are mixed with a drug that collects in a
particular organ in the body.
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If we then inject the drug into the body, then by detecting
the 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 ray
that 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 gas
ventilation
perfusion
A blood clot in the right lung is preventing
blood from reaching the lower lobe of the
right lung, although the ventilation image
shows 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
PET
(Positron Emission Tomography)
Cyclotron
Used 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.
tumour
heart
kidney
Combined PET/CT
Radiotherapy
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 treatment
A 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 delivered
to the benefit of the patient.
Acknowledgements
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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
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This lesson was developed by Adam Gibson, Jeff Jones,
David Sang, Angela Newing, Nicola Hannam and Emily
Cook
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We have attempted to obtain permission and acknowledge
the contributor of every image. If we have inadvertently
used images in error, please contact us.