Medical Uses of Radiation

Different types of ionising radiation have different medical applications, chosen because of their penetrating power and ionising ability.

Diagnostic uses

X-rays (imaging):

• X-rays pass through soft tissue but are absorbed by bone and dense tissue.
• A detector (photographic film or digital sensor) behind the patient creates an image.
• Used for detecting fractures, dental problems, chest infections.

Gamma cameras (tracer studies):

• A patient ingests or is injected with a gamma-emitting radioisotope (tracer).
• A gamma camera outside the body detects the emitted gamma rays.
• Used to image organs (thyroid, kidneys, heart) and detect abnormalities.
• The tracer must have a short half-life (hours) so it decays quickly and minimises exposure.

PET scans:

• Use positron-emitting tracers (e.g. fluorine-18).
• Produce detailed 3D images of metabolic activity.

Therapeutic uses

Radiotherapy (cancer treatment):

• High-energy gamma rays or X-rays are aimed at tumours to kill cancer cells.
• The beam is rotated around the patient so healthy tissue receives a lower dose.
• Multiple sessions are needed because not all cancer cells are killed in one treatment.

Targeted radiotherapy:

• Radioactive sources (e.g. iodine-131 for thyroid cancer) are taken internally and concentrate in the target organ.

Why gamma is used for tracers

• Gamma penetrates the body (alpha and beta would be stopped before reaching the detector).
• Gamma is the least ionising (lower risk of cell damage).
• Short half-life tracers (e.g. technetium-99m, $t_{1/2} = 6$ hours) decay quickly, reducing long-term exposure.

Common errors and how to correct them

• Saying alpha particles are used as medical tracers. Alpha cannot penetrate the body; gamma is used.
• Confusing tracers (diagnosis) with radiotherapy (treatment).

How to apply this in an exam

Name the specific type of radiation used and explain why (penetrating power, half-life). Describe the safety measures taken to protect the patient and medical staff.