In simple terms, radiotherapy means treatment with ionizing rays; obtained from different sources. External radiation is delivered mainly by Linear accelerators (high energy X-rays). Brachytherapy (internal radiation) is obtained from radioactive substances placed inside or against the tumor area. To understand how ionizing rays work, you must understand how cancer cells affect your body.
The goal of radiation therapy is to damage and eventually destroy the cancer cells, but the rays cannot distinguish between normal and malignant cells.
The success of irradiation lies in the fact that malignant cells are more sensitive to irradiation than normal cells. The goal of irradiation is therefore to irradiate until the malignant cells have been killed or sterilized. The surrounding normal tissue is, however, still capable of complete recovery.
In certain phases of division cells are more sensitive than in other, dormant phases.
To irradiate as many of the cells as possible in the sensitive phase, the treatments are fractionated; in other words, they are spread over a period of time.
Another reason for fractionation is to give the normal cells, which recover faster than malignant cells, a chance to recuperate. This is why the total required dose is not given in one treatment. The sensitivity of the various types of tissues and the various organs differ, thus the number of treatments for different diagnoses will inevitably also differ. The number of treatments prescribed bears no relation to the degree to which the cancer has advanced, therefore, if you are to receive thirty-five treatments and another person receives only five, you cannot assume that your prognosis is worse than theirs. The dose administered, the number of treatments and the specific diagnosis are very closely linked. It is important to understand that because irradiation is used differently for the different conditions, it is not wise to compare treatments, symptoms or side effects.
Irradiation is only done during the week, and sometimes it is interrupted for a day when the machine is being serviced or work is being done on the machine.