Knowledge Base

How does radiation work in radiotherapy?

Ionizing radiation (including X-rays) has many applications in medicine and biology. Unlike radiology, radiotherapy uses ionizing radiation for therapeutic (treatment) rather than diagnostic purposes, and uses higher energy X-rays (or rarely other radiation types, such as protons). Radiation therapy is a localized treatment to destroy cancer cells by irradiating them, while sparing the surrounding normal tissues as much as possible. The rays go through the skin and tissues and cause damage to the DNA of their cells. During irradiation, ionizing radiation interacts with the cell content by producing physical-chemical reactions that will damage the DNA, During irradiation, ionizing radiation interacts with the cell content by producing physical-chemical reactions that will damage the DNA (DNA strand breaks).

• Following DNA damage, the cell may manage to correctly repair the DNA lesions and will survive.
• However, when the damage is too severe, the cell will die.

The effectiveness of radiotherapy (i.e. its capacity to kill cancer cells) depends largely on the dose delivered to the tumor. Therefore, it is important to determine the dose that will give the highest effect with the least damage to normal tissues.

Importantly, although radiation therapy is a localized treatment, 5 to 10% of patients, who are considered “hypersensitive”, will develop complications following radiotherapy. These complications, or toxicities, are due to the unwanted irradiation of normal tissues located within or near the radiation field. These toxicities are classified into two categories: acute toxicities when they occur during treatment or within 3 months after the treatment end; late toxicities when they occur later than 3 months after the treatment end. The goal of radiation therapy is to maximize the dose received by the tumor volume to kill as many tumor cells as possible and to limit the dose received by the surrounding healthy tissues to avoid complications.