[Poster] Pre-treatment Quality Assurance for Flattening Filter Free Dynamic Arcs: a Detector Comparison

Laure Parent¹, Maxime Goubert¹, François Husson²
1 Institut Universitaire du Cancer Toulouse – Oncopole, Ingénierie et de Physique Médicale,Toulouse, France
2 Dosisoft S.A., Cachan, France

Presented at ESTRO 2018

Introduction: Quality control of VMAT plan is a time consuming task for all medical physics team. The PTW Octavius matrix is widely used for the validation of VMAT plans. The main disadvantage of this system is that the measurement is done only in a fixed plan that is not always representative of the delivered dose. The time required for the set-up is also quite significant.

Pre-treatment quality assurance (QA) with flattening filter free (FFF) beams is challenging because of the high dose rate and the required spatial resolution as small fields are usually used. Our current clinical practice is to perform pre-treatment QA with a chamber array in a rotational phantom. This study investigates the replacement of this process by an electronic portal imager (EPI) measurement without a phantom in place in order to shorten the QA time on the machine.

Conclusion: EPIbeam offers an alternative solution for patient delivery QC using the iViewGT panel. The advantages are in the set-up time, the spatial resolution of the detector and the perpendicularity of the panel with the beam fluence. Although the detector is always in front of the beam and is not sensitive to gantry error position, it should be noted that the influence of the gantry rotation is taken into account by a specific EPID-arm sag-effect correction applied on the measurement that may returns possible deviations in comparison to ideal operating conditions.