The term external radiation therapy describes a treatment in which the radiation beam is produced outside the body by a device called a linear particle accelerator.
External radiation therapy is alocal cancer treatment in which cancer cells are killed by irradiating them with a radiation beam composed of photons (or sometimes electrons). This radiation, called “ionizing” because it can break away electrons from atoms (a process called ionization) inside the cells, is produced by machines called linear particle accelerators.. The beam of photons or electrons is directed to the area to be treated: the tumor. External radiation therapy is also called transcutaneous radiotherapy because the radiation passes through the skin to reach the tumor. The beam passes through normal tissue, but the dose deposited is higher at the tumor site than in healthy organs, thus limiting the side effects.
The number of radiotherapy sessions depends on :the tumor location; the indication(tumor type, adjuvant or neoadjuvant radiotherapy, radiotherapy combined with chemotherapy, curative/palliative radiotherapy); the technique of irradiation(3D conformal radiotherapy, intensity-modulated conformal radiotherapy, stereotactic radiotherapy).
The radiation doses also are determined in function of the tumor type (some cancers are considered to be more “radiosensitive” than others), location, indication, and tolerance of the organs treated or around the irradiation area. Therefore, the optimal doses, total treatment duration, and number of radiotherapy sessions are specifically calculated for each patient.