Читать книгу The Cancer Directory - Dr. Daniel Rosy - Страница 103

The most common type of radiotherapy is the use of an external radiation source produced by a linear accelerator, a large machine that delivers a precise dose of radiation to a particular site of the body. An alternative form uses internal radiation, where a radioactive source – such as radioactive needles or ‘seeds’ – is temporarily placed in the part of the body affected by tumour, such as the womb or prostate gland.

Different types of X-rays are used as each has a different level of penetration. Laboratory evidence tells us that radiotherapy works by damaging DNA in the nucleus of rapidly dividing cells. The DNA molecule has a particular sequence, creating a vital code for proteins that have important functions both inside and outside the cell. Radiation breaks the ‘backbone’ of the DNA molecule so that, when the strands join back together, the coding sequence is altered, resulting in the cell’s death. It only affects cells that are reproducing, which is why radiotherapy is given in multiple doses – to catch the cells at different phases of their growth cycle.

Radiotherapy damages cancer cells whereas normal tissue is usually able to repair itself. We have learned how to exploit this difference, and establish a balance between destroying cancer cells while causing minimal damage to normal tissues. Also, the delivery systems for radiation are now so precise that it is almost possible to irradiate only the tumour. However, if the individual survives for some time after radiotherapy, it is possible for a new, different second cancer to arise as a result of the radiotherapy treatment.