Promoteur : Prof. P. Mégret

Résumé :

The interaction of radiation with living entities is generally associated with damages of their fundamental structures, i.e. the DNA, which can later induce malignant effects such as chromosome aberrations, cell necrosis or apoptosis. Depending on the amount and type of radiation exposure, on a macroscopic scale this could translate in skin erythema, hair loss, sterility, cataract, fetal decease, teratogenesis, cancer, hereditary defects or death. It appears clear that the exposures to ionizing radiation should be justified, limited if not totally avoided. However, radiation is silent, tasteless, invisible and cannot be perceived in any way by humans before that its effects irremediably occurred. Luckily, with the evolution of science, many devices able to quantify radiation exposures have been developed. Detectors made of luminescent materials represent an elegant example. After a radiation exposure and under controlled conditions, these crystals glow and the emitted light can be correlated with the received amount of radiation dose. As a consequence, this technology has been used for decades to monitor radiation doses received by exposed workers or for retrospective analyses after nuclear incidents.

On the other hand, ionizing radiation can be used to cure cancer. The latter is the case of radiotherapy, where finely tuned particle beams are shot against the tumor volume to selectively kill the cancer cells. Also here, due to their small, cheap and passive nature, bunches of luminescent detectors can be used to judge the precision of the treatment and to assess possible changes in its effectiveness within the cancer volume.

However, the main drawback of luminescent detectors is that they do not record radiation exposure information independently from the nature of the radiation exposure: for sparsely ionizing radiation as photons they have high efficiency, while a strong efficiency decrease occurs for measuring strongly ionizing particles as the ones present in space or close to the edges of cancer radiotherapy treatments. This has led to a progressive replacement of these detectors with more sophisticated and expensive ones.

In this Thesis, an accurate study of the nanoscopic structure of energy deposition gave new insights and a complete description of the efficiency changes of luminescent detectors, a tool to predict the efficiency in known radiation environments and a new methodology to extract radiation quality information within cancer radiotherapy treated volumes.