[Dosimetric impact of the 2D motion of a platform simulating breathing during a dynamic mode treatment]. / Impact dosimétrique du mouvement 2D d'une plateforme simulant la respiration lors d'un traitement en mode dynamique.

Breathing-adapted techniques in external radiotherapy lead to the improvement of the taken into account of the tumour motion during the patient treatment. Indeed, this motion involves dosimetric uncertainties, in particular during a dynamic treatment (intensity-modulated radiation therapy, dynamic wedge...). As tumoral movement is complex and is carried out in various directions of space, a dynamic platform moving in one or two plans was conceived. This article approaches the technical aspects of design and functioning of this prototype. A study of the dosimetric effects of the respiratory movement on one and two plans during a dynamic treatment without gating will be presented. Films were irradiated while varying the rates with wedged fields at various speeds. The penumbra of beams were compared with the static case and appeared twice broader in the majority of the cases. The results highlighted the contributions of the longitudinal and the axial components of the motion on the form of the dose distribution. These results were completed with gamma index measurements to determine an internal margin. Moreover, this platform proves to be a promising tool for breathing-adapted treatment, in particularly to test the synchronisation of RPM system in fluoroscopic mode in board imaging system.

A perturbation method for modeling the thermal sensitivity of surface transverse waves.

A perturbation approach has been developed to predict the sensitivity of surface transverse waves (STW) to quasi-static temperature effects. This approach is based on the combination of unperturbed STW characteristics and thermoelastic properties of the substrate. The unperturbed STW parameters are calculated taking piezoelectricity into account. Both cases of STW propagating under shallow groove or thin metal strip gratings are studied. An analytical expression of the first order temperature coefficient is obtained in the case of grooves. A simplified calculation is proposed for thin metal strip grating devices. Results are compared to available experimental data. Possible improvements of this model are finally discussed.

Design and test of 3 GHz, fundamental mode surface transverse wave resonators on quartz.

Surface transverse wave (STW) resonators, based on the propagation of high velocity shear horizontal waves on Y-rotated quartz were designed, fabricated and tested. A model is presented to predict the resonant frequency of a 3-grating structure as a function of design parameters such as periodicities, metal thickness, and finger-to-gap ratio. Experimental devices have been fabricated by direct e-beam lithography with linewidth geometries in the range of 0.3-0.5 mum, and an operating frequency close to 3 GHz in fundamental mode. Two different designs using either a quasi synchronous structure (type 1) or a change of periodicity inside the cavity (type 2) were tested. The best experimental factor of merit is close to the best results already published for quartz STW resonators.