A doctor uses a gamma-emitting radioactive isotope to carry out chemotherapy on a patient who has a tumour. Explain why a gamma emitter is chosen for this purpose, and explain one disadvantage of this treatment for the patient.

OCR A-Level Physics A (H556) — 6.4 Medical imaging · Explain · 5 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Gamma radiation is used in medicine to treat cancerous tumours. The radiation is directed at the affected area of the body from outside.

Model answer (5 marks)

Gamma radiation is the most penetrating form of nuclear radiation, so it can reach tumour cells that are deep inside the body.

When the gamma rays are absorbed by the cancerous cells, the energy deposited damages their DNA, which kills the cells or stops them from dividing, thereby destroying the tumour.

A disadvantage is that the same gamma rays also irradiate healthy tissue around the tumour, which can damage normal cells and cause harmful side effects such as skin burns, fatigue or secondary cancers.

Examiner tips

  • Use the word ‘penetrating’ to show understanding of gamma rays’ properties. Mention the tumour‑cell damage mechanism (DNA damage).
  • State the specific disadvantage (damage to healthy tissue) to gain the final mark.

Common mistakes

  • Confusing gamma rays with X‑rays or beta particles. Failing to mention the effect on healthy cells as the disadvantage.

Mark scheme (5 marks)

  1. Gamma radiation is the most penetrating type of nuclear radiation
  2. So gamma radiation can reach the tumour / cancerous cells deep inside the body
  3. The gamma radiation is absorbed by the cancerous cells
  4. This kills the cancerous cells / destroys the tumour
  5. Surrounding healthy cells may also be irradiated and destroyed, causing harmful side effects

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