WHAT IS RADIOTHERAPY?
X rays were discovered in 1895 by the German physicist Wilhelm Konrad Roentgen, who was the first to use them for diagnostic purposes. Differently, it is debatable who was the first to apply X rays to treatment. Radiotherapy is now used almost exclusively to treat malignant tumors.
During external beam radiotherapy with a linear accelerator, the patient does not come into contact with the machine, and does not feel any discomfort during treatment. After the daily session of therapy, which generally lasts several minutes, the patient is not 'radioactive', and is thus not harmful to others. In most cases, the patient goes home after therapy and returns the next day at the appointed time. Usually, there is one session a day; in a few cases there may be two sessions a day. Therapy is administered from Monday to Friday. In some cases, radiotherapy is associated with antiblastic chemotherapy (i.e. 'radio-chemotherapy'). Radiation acts only on the tumor, not on the whole body.
Different tumors respond differently to radiation in terms of entity and speed of tumor regression. The response to radiation is called 'radiosensitivity', and tumors are classified: highly radiosensitive, of an intermediate sensitivity, and radio-resistant.

HOW DOES RADIOTHERAPY WORK?
Radiotherapy is a powerful tool for the loco-regional cure of tumors. It exploits the capacity of X rays to destroy neoplastic cells, which are more sensitive than healthy cells to radiation. Radiotherapy is based on this difference: the aim is to destroy tumor cells while sparing nearby normal cells.
The most recent high-energy linear accelerators are able to target the tumor while sparing the healthy surrounding tissue to a much greater extent compared with the obsolete cobalt therapy. Deep-sited tumors benefit from radiation fields (photons and electrons) that have high nominal energy able to release doses at greater depths. Modern linear accelerators comprise control systems that abort the procedure when it does not conform to quality standards that are pre-fixed and controlled by qualified personnel. In this context, the expert medical-physicist monitors the characteristics of the radiation beam and makes a series of quality controls that are, by law, recorded, and that serve to eliminate sources of error.

AIMS OF RADIOTHERAPY
Radical or curative radiation aims at curing the tumor. However, it can also target areas, e.g. lymphatic drainage areas, which appear healthy, but are considered to be at high risk of subclinical disease. This is known as 'preventive' radiation.
Occasionally, the characteristics of a neoplastic disease are such that a cure is considered improbable. In such cases, 'palliative' radiotherapy can be used to prolong survival and to slow tumor growth thereby improving quality of life.

RADIOTHERAPY ASSOCIATED WITH SURGERY
Relapses can occur after surgery or after radiotherapy. In some instances, radiotherapy is combined with surgery in an attempt to improve the rate of disease control and long-term survival. The rationale is that radiotherapy destroys tumor infiltrations in nearby tissue (which are often not visible to the naked eye) that were not removed or not removable during surgery. Radiotherapy may be administered before, after or during surgery.

RADIOTHERAPY ASSOCIATED WITH CHEMOTHERAPY
Radiotherapy and chemotherapy can be administered together, or radiotherapy can be administered before chemotherapy and vice versa. Some protocols entail pre- and post-surgery radio-chemotherapy.