A hospital uses a gamma-emitting radioactive isotope in chemotherapy treatment to destroy cancerous cells in a patient. Explain why a gamma emitter is chosen for this purpose, and describe one significant hazard associated with this treatment.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Gamma radiation is used in chemotherapy to target cancerous cells inside the body. The radioactive source is positioned outside the patient and the beam is directed towards the tumour.
Model answer (5 marks)
Gamma radiation is chosen because it has the greatest penetrating power, allowing the beam to reach tumours deep inside the body while passing through surrounding tissue.
It is the least ionising of the common radioactive emissions, so it is less likely to damage healthy cells as it travels through the body compared with alpha or beta particles.
The tumour cells absorb the energy from the gamma photons and are destroyed by ionisation and free‑radical damage.
However, the beam cannot be aimed with perfect precision; the radiation spreads and irradiates surrounding healthy tissue.
Thus a significant hazard is that healthy cells may also be damaged, leading to harmful side effects for the patient.
It is the least ionising of the common radioactive emissions, so it is less likely to damage healthy cells as it travels through the body compared with alpha or beta particles.
The tumour cells absorb the energy from the gamma photons and are destroyed by ionisation and free‑radical damage.
However, the beam cannot be aimed with perfect precision; the radiation spreads and irradiates surrounding healthy tissue.
Thus a significant hazard is that healthy cells may also be damaged, leading to harmful side effects for the patient.
Examiner tips
- Use the exact phrases ‘penetrating power’ and ‘least ionising’ to gain full marks. Explain both the benefit (deep penetration) and the drawback (damage to healthy tissue). Keep the answer concise and structured in five clear points.
Common mistakes
- Confusing gamma with alpha or beta radiation. Failing to mention the reduced ionising nature. Over‑extending the answer with unnecessary details or irrelevant information.
Mark scheme (5 marks)
- Gamma radiation has the most penetrating power / can pass through body tissue to reach internal tumours
- Gamma radiation is least ionising, so it is less likely to damage healthy tissue as it travels through compared to alpha or beta
- The cancerous cells absorb the energy from the gamma radiation and are killed / destroyed
- It is difficult to accurately target only the cancerous cells / the gamma beam cannot be directed with complete precision
- Surrounding healthy cells may also be irradiated and destroyed, causing harmful side effects to the patient
Key terms in this question
Related
- All OCR A-Level Physics A (H556) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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