We all experience radiation in our daily lives, as visible light or the warmth generated by the absorption of sunlight. Radiation of higher energies, called X-rays and gamma rays, can penetrate deep into the human body. Their absorption in tissues is used in medicine for imaging and cancer therapy.

Some minerals and elements emit radiation through decay mechanisms and are therefore called radioactive. Imaging and modern radiation machines produce radiation for medical purposes. With advanced technology, it is possible to accurately focus the radiation to any point in the body. In this way, it can be used to target and destroy tumours.

Radiation is an energy that is transported in the form of electromagnetic waves or particles. Visible light and sunbeams are radiation forms in the micrometer and lower wavelength range.  Energetically much stronger and invisible are radiation types like X-rays and gamma rays. These penetrate tissues and can, therefore, be used for imaging or cancer therapy purposes.

The decay of some minerals and elements, which are therefore called  “radioactive”, can generate radiation that is used for medical purposes.  In addition to radioactive sources, radiation in the form of x- and gamma rays are also produced by man in modern imaging and radiotherapy machines. One common way is to accelerate electrons and generate radiation through collision with certain materials. Radiation is categorised by the level of energy. The impact it has on cells is important and also depends on the nature and origin of the cells.

With respect to medical radiation, the radiation source can be placed inside the body (example of brachytherapy) or focused on the tumor from outside the body (external radiation therapy).  Radiation emitted from radioactive pellets is limited in their penetration depth in tissue.
Consequently, the maximum damage in tumor cells is achieved if the pellets can be placed directly into or at least closely adjacent to the tumor. For external radiation sources, the maximum effect is achieved by directing a number of radiation beams from different angles directly into the tumor. This way the surrounding healthy tissue receives very little from the radiation.

The most commonly used radiation in modern radiation oncology consists of high energy photons. In addition to these photon beams radiotherapy also uses charged particle beams of electrons, protons or even heavier ions to destroy tumors. Common to these beams is their limited penetration depth in tissue which can be controlled by their initial kinetic energy.