[Dosimetric quality control in stereotactic radiotherapy with the aid of radiosensitivity]

Typical dosimeters used in stereotactic radiation therapy, such as ionization chambers, films, and thermoluminescent diodes, allow basic physical measurements. They are, however, neither well suited to discern small target volumes with high dose gradient, nor suitable for three-dimensional (3D) dose measurements. Gel dosimetry is becoming more and more interesting, owing to magnetic resonance imaging (MRI). It permits isocenter position planning verification of accuracy and the precision of the 3D dose mapping in the brain (when irradiated in realistic conditions), especially when several different targets are concerned. Many authors have assessed stereotactic radiation therapy quality control using different gels, and different irradiation procedures. This paper consists of the review of these different methods to assess quality control. Gel dosimetry cannot provide absolute dose measurements. However, gels can be used to check the 3D dose mapping with a high degree of detail. In our experiment, the difference between the stereotactic frame center and the isocenter is about 1 mm. The difference between the theoretical isodoses obtained by the treatment planning system and the experimental isodoses obtained by the MRI gray level calibration is also about 1 mm, the order of magnitude of the MRI pixel size.