Verification dosimetrique de la modulation d'intensite par accelerateur classique equipe d'un collimateur multilame

In intensity modulated conformal radiotherapy, it is essential to know the exact radiation dose in the target volume, in the organs at risk, and in the regions of steep dose gradient. The treatment planning, which provides a guideline during the optimisation of intensity modulated radiotherapy, must be thoroughly and specifically validated. In this context, 3 levels of experimental dosimetry have been differentiated: i) the dosimetric study of small uniform segments or elementary beams; ii) the dosimetric study of intensity modulated beams in a water phantom; and iii) the preclinical dosimetric evaluation in anthropomorphic phantoms of geometry-based segmental intensity modulated radiotherapy. The results of this study showed the following: i) the small-field dosimetric characteristics were strongly influenced by the geometric adjustment of the collimating equipment; ii) it demonstrated the necessity for rigorous characterisation of the penumbra of the segments; iii) it focussed attention on the delicate aspect of narrow angular beam separation. At the present time, in intensity modulation the precise dosimetric assessment is just as imperative as the treatment planning and the therapy-related technology.