Suggestion for an extended quality assurance in 4D CT and its function in gated radiotherapy using a motion phantom

Abstract

The use of a retrospective 4D CT has many advantages over a conventional CT because of the additional information of tumour and organ motion during one respiratory cycle. This enables the determination of patient individual treatment margins and more reliable estimation of site effects. Furthermore a 4D CT allows the determination of parameters for respiration gated radiotherapy such as gating window and duty cycle. However, the generation of the CT images is quite different in comparison of a conventional CT. 4D CT scans use a multi-slice CT scan, which permits evaluation of all 'bins' of the 4D data set. For this different CT image generation a new quality assurance is necessary, controlling the new features and correlations of the additional components. We have developed an extended quality assurance procedure, which controls the geometric size as well as the extension of motion. Because the external waveform is monitored by a signal provider placed on patient's abdomen or chest, the synchronous motion of external signal provider with internal pictured objects of interests is to be checked. Another important test for the treatment planning system concerns the object density (referring to the Hounsfield Units (HU)) without and with motion. © 2009 Springer-Verlag.