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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 better for treating a brain tumour, we can use the linear attenuation equation:
I = I_0 e^{- rac{ ext{µ} imes x}{ ext{cm}}}
Where:
- is the initial intensity,
- is the intensity after passing through the material,
- is the linear attenuation coefficient,
- is the depth (11 cm).
For 100 keV photons:
- This results in
For 500 keV photons:
- This results in
Since 500 keV photons allow more radiation to reach the tumour (0.38 vs 0.19), they are better at treating the brain tumour and cause less damage to surrounding tissue.
Step 2
Discuss whether it would be better to use aluminium or copper to filter the X-rays in Question 03.1.
Answer
Considering the linear attenuation coefficients:
- For 100 keV:
- Aluminium: 0.44 cm^-1
- Copper: 3.8 cm^-1
- For 500 keV:
- Aluminium: 0.23 cm^-1
- Copper: 0.73 cm^-1
At 100 keV, copper significantly attenuates X-rays more than aluminium, which can lead to higher exposure of healthy tissues. While for 500 keV, aluminium provides better filtration with relatively lower attenuation.
Thus, aluminium would be more effective at limiting the dose to healthy tissues while still allowing sufficient treatment energy to reach the tumour.
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: This technique ensures accurate targeting of the beam, thereby reducing unnecessary exposure to surrounding healthy tissues. By precisely locating the tumour, the X-ray treatment can be better aligned, focusing the radiation specifically on the cancerous cells.