Radiotherapy is the use of forms of radiation to treat disease. It is essentially delivered in two forms – either electromagnetic (for example X-rays, gamma rays) or particulate (for example protons, neutrons). Radiotherapy is similar to chemotherapy in that it can lead to the destruction of cancer cells. Although normal cells are also damaged by radiotherapy, cancer cells are generally more sensitive. This means that a large enough dose to kill cancer cells can be given while still allowing normal tissue to recover. This requires a careful balance between the radiation dose and an acceptable level of normal tissue damage – this is known as the therapeutic ratio. The effect that radiation has on normal tissue is variable and certain tissue types are particularly sensitive, for example, central nervous system tissue, eyes, lungs, bladder and bowel.
The aims of radiotherapy treatment are:
- To kill cancer cells;
- To cause minimum damage to healthy cells. Uses of radiotherapy
- Radiotherapy can be used as the sole treatment modality.
- Radiotherapy can be used in conjunction with chemotherapy or surgery.
- Radiotherapy can be used to control symptoms in an emergency situation. For example, if a tumour is compressing the spinal cord, radiotherapy can alleviate the pressure and prevent permanent damage.
- Radiotherapy may be palliative; for example, to help control symptoms or discomfort, such as bleeding or pain. How is radiotherapy delivered?
- Radiotherapy is delivered in small, frequent doses (to minimize side effects) often over a period of 4-6 weeks. Radiotherapy is usually given from Monday to Friday to enable healthy tissue to recover and survive the whole treatment programme.
- Colbalt Units or non-radioactive units called linear accelerators deliver the radiotherapy.
- The radiotherapy dose is prescribed in Gray (Gy) or Centigray (cGy).
There are three main ways of delivering radiotherapy:
- External radiotherapy or teletherapy is the delivery of beams produced by a source outside of the body.
- Internal radiotherapy or brachytherapy is the delivery of the radioactive source via an implanted unit.
- Unsealed source is the process of attaching a radioactive isotope to a chemical / metabolite and injecting into the body. This has been used in neuroblastoma patients.
Prior to commencing treatment, consultation, planning and simulation is required to determine the most appropriate source and dose of radiotherapy. To maintain accuracy of the radiotherapy beam, it is essential that the area of the body receiving the dose remains immobilised throughout each treatment. Often this will be achieved by providing the child with a mould or mask which will hold the area still and protect surrounding tissues. Furthermore, skin marking using ink is another method that ensures accurate delivery of radiotherapy to the correct site. The final stage of planning is a simulation using diagnostic X-rays to check the prescribed treatment plan.
Treatment toxicity (side effects)
The side effects will depend on the area that the radiotherapy is given.
- Skin – Often redness will be seen within 7 days of treatment. Dryness is common if the sweat glands have been damaged. When extreme damage has been caused to the inner skin layers, leakage of fluid can become a serious complication.
- Gastrointestinal – The mouth can become dry due to damage to the salivary glands which can result in pain and stomatitis (inflammation of the oral mucosa).
- Brain toxicity caused by inflammation can lead to raised intracranial pressure.
- Haematological – Anaemia, thrombocytopenia, neutropenia and the risk of viral infections are possible side effects.