ESTRO 2024 - Abstract Book
S4175
Physics - Intra-fraction motion management and real-time adaptive radiotherapy
ESTRO 2024
translational directions, a PTV margin reduction is not yet recommended due to the outliers in sup/inf. More data will have to be collected to extend this audit with more representative patient data now the process has been refined. Finally, this audit confirmed successful application and valuable use of IFI CBCT (both full and partial arc) in repeated breath-hold for high-contrast imaging areas such as lung SABR.
Keywords: lung SABR, DIBH, intra-fractional CBCT imaging
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Digital Poster
Consequences of couch sag and couch movement for optical surrogate systems in respiratory guided CT
Niklas Lackner 1,2,3 , Lisa Dietrich 1,2,3 , Christoph Bert 1,2,3 , Andre Karius 1,2,3 , Rainer Fietkau 1,2,3 , Juliane Szkitsak 1,2,3
1 Universitätsklinikum Erlangen, Radiation Oncology, Erlangen, Germany. 2 Friedrich Alexander Universität, Faculty of Sciences, Erlangen-Nürnberg, Germany. 3 Comprehensive Cancer Center, Erlangen-EMN, Erlangen, Germany
Purpose/Objective:
For many years, respiratory-guided CT has employed breathing motion surrogates, such as the emission of infrared light and the detection of a reflector block placed on the patient's thorax or collecting data from surface scanning. Optical surrogate systems not mounted on the CT couch must correct for couch motion, thus respiratory signals might be unreliable during table movement [1]. In the worst-case scenario, patient re-scanning may be required to collect sufficient data, resulting in an undesired extra dose. Different studies have reported a baseline drift for breathing curves using different surrogate systems likely related to weight-dependent table sag [2],[3]. Visual breathing guidance devices based on aforementioned surrogate systems suffering from couch motion and sag artifacts might confuse the patient. This study aimed to evaluate the impact of couch movement and couch sag in four-dimensional computed tomography (4DCT) and deep-inspiration breath-hold (DIBH) CT.
Material/Methods:
CT scans were acquired using a SOMATOM go.Open Pro scanner (Siemens Healthcare, Forchheim, Germany). For the measurements, we used a static phantom placed in a typical patient position (see Figure 1A). We compared SimRT (version 7.2, VisionRT, London, UK) with RGSC (version 1.1.25.0, Varian Medical Systems, Inc. Palo Alto, CA, USA) and used a Polaris Spectra (NDI, Waterloo, Canada) coupled with a radiation detector GM10 (Black Cat Systems, Westminster, MD, USA) as ground truth reference. The beam-on signal from the different systems was used to match breathing curves. We assessed the impact of weight, as well as the consequent baseline drift attributed to table sag and subsequently added lead blocks, each weighing 13 kg. Table sag was compared to the weightless situation. In a second step, the longitudinal measurement, the influence of the phantom position on the sag was determined for 7 different positions, at different loads.
In our clinical workflow for the DIBH CT scans, we train the breath-hold scenarios with the patients using a visual guidance device, fed by data from SimRT, the Real Time Coach (VisionRT). Then we set a threshold band at ± 2.5 mm
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