Abstract # 2057 Repositioning Accuracy Of Two Different Mask Systems: A Comparison By True 3D-3D Matching With Cone-Beam CT

Presenter: Boda-Heggemann, Judit

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In this study we assessed and compared the magnitude of the interfractional translational and rotational setup errors in two established mask systems based on volumetric data (true 3D-3D matching) acquired with a CBCT.

For fractionated stereotactic radiotherapy, reliable patient-immobilisation and accurate interfractional isocenter-repositioning are essential. Non-invasive cranial fixation has been performed with several mask-based devices; however, these can exhibit a significant daily variation in target alignment. Positioning accuracy of mask systems has been assessed by X-ray films, electronic portal imaging or repeated CT/MRI scans outside the treatment room, which allow only a 2D or 2D/3D matching or are not directly linked to the actual treatment. KV cone-beam CT (CBCT) implemented on board of a linear accelerator allows daily assessment of positioning errors (in 6 degrees of freedom) with a minimal dose exposure (2.1 mGy) and time requirements.

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