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X-ray photons can be used to treat cancerous tumours in radiotherapy - AQA - A-Level Physics - Question 3 - 2020 - Paper 6
Question 3
X-ray photons can be used to treat cancerous tumours in radiotherapy. Some photons are absorbed by healthy tissue before they reach the tumour. Photons with a range... show full transcript
Worked Solution & Example Answer:X-ray photons can be used to treat cancerous tumours in radiotherapy - AQA - A-Level Physics - Question 3 - 2020 - Paper 6
Step 1
Deduce whether photons of energy 100 keV or 500 keV are better for treating a brain tumour at a depth of 11 cm.
Answer
To determine which photon energy is more effective, we need to calculate the intensity of the X-ray photons at a depth of 11 cm for both energies using the formula:
where:
- is the initial intensity (assumed to be 1 for comparison),
- is the linear attenuation coefficient,
- is the depth (11 cm).
For 100 keV:
- Calculate .
- This equals .
For 500 keV:
- Calculate .
- This equals .
Since , photons of energy 500 keV are better for treating the tumour at this depth, as they penetrate deeper with less absorption in healthy tissue.
Step 2
Discuss whether it would be better to use aluminium or copper to filter the X-rays in Question 03.1.
Answer
While both aluminium and copper can be used as filters, the choice depends on the energy of the X-rays being emitted. At 100 keV, aluminium has a linear attenuation coefficient of 0.44 cm⁻¹, while copper has a much higher coefficient of 3.8 cm⁻¹. This means copper would absorb significantly more X-rays, reducing overall beam intensity and possibly affecting the treatment effectiveness.
At 500 keV, aluminium's coefficient drops to 0.23, whereas copper's is 0.73. Here, aluminium is again preferable as it minimizes absorption while still allowing more X-rays to pass through.
Thus, for both energy levels, aluminium is the superior choice for filtering, preserving the dose delivered to the tumour and minimizing damage to healthy cells.
Step 3
State and explain one other method used to limit exposure of healthy cells during X-ray radiotherapy.
Answer
Method: Use of scans to locate the tumour.
Explanation: By accurately locating the tumour prior to treatment, doctors can target the radiation beam more precisely, minimizing exposure to surrounding healthy tissues. This could involve imaging techniques like MRI or CT scans, which provide detailed images of the tumour's location and size, allowing for safer and more effective treatment planning.