X-ray photons are used in radiotherapy to target cancerous cells deep within a patient. However, a significant fraction of these photons is attenuated by healthy intervening tissues before reaching the targeted site. High-energy X-ray machines produce a spectrum of photon energies.
Table 1 shows the linear attenuation coefficients of soft liver tissue for X-ray photons at energies of 250 keV250\text{ keV}250 keV and 600 keV600\text{ keV}600 keV.
Table 1
| Energy / keV\text{keV}keV | Linear attenuation coefficient of soft liver tissue / cm−1\text{cm}^{-1}cm−1 |
|---|---|
| 250 | 0.14 |
| 600 | 0.082 |
Deduce whether photons of energy 250 keV250\text{ keV}250 keV or 600 keV600\text{ keV}600 keV are more suitable for treating a localized liver tumor located at a depth of 11.0 cm. Support your answer with a calculation.
Metal filters are positioned in the path of the X-ray beam to minimize dose absorption by healthy superficial tissues. Table 2 provides linear attenuation coefficient data for two potential filter materials: Aluminium and Copper.
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 |
|---|---|---|
| 250 | 0.32 | 1.15 |
| 600 | 0.21 | 0.65 |
Using the information provided, discuss whether Aluminium or Copper would be the superior choice of filter for the therapeutic scenario described in part (a). No calculations are required.
State and explain one other method employed during external beam radiotherapy to limit radiation exposure to healthy surrounding tissues.
