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 of energies are generated in an X-ray machine.
Table 1 shows the linear attenuation coefficient of muscle tissue for photons of energy 150 keV150\text{ keV}150 keV and 400 keV400\text{ keV}400 keV.
Table 1
| Energy / keV\text{keV}keV | Linear attenuation coefficient of muscle tissue / cm−1\text{cm}^{-1}cm−1 |
|---|---|
| 150 | 0.16 |
| 400 | 0.095 |
Deduce whether photons of energy 150 keV150\text{ keV}150 keV or 400 keV400\text{ keV}400 keV are better for treating a muscle tumour at a depth of 9.5 cm.
Metal filters are used in X-ray machines to limit the damage to healthy tissues. Table 2 gives data for possible filter materials.
Table 2
| Energy / keV\text{keV}keV | Linear attenuation coefficient of Aluminium / cm−1\text{cm}^{-1}cm−1 | Linear attenuation coefficient of Copper / cm−1\text{cm}^{-1}cm−1 |
|---|---|---|
| 150 | 0.38 | 2.50 |
| 400 | 0.25 | 0.85 |
Discuss whether it would be better to use aluminium or copper to filter the X-rays in Part 1. No calculations are required.
State and explain one other method used to limit exposure of healthy cells during X-ray radiotherapy.
