ESTRO 2023 - Abstract Book

S1639

Digital Posters

ESTRO 2023

Conclusion DTRT was successfully delivered with gating on a TrueBeam system for the first time. Machine accuracy was similar to delivery without gating. Gating substantially improved the dosimetric plan quality as compared to deliveries without gating. This work was partially supported by Varian Medical Systems.

PO-1894 Ultrasound is preferable to MRI as imaging modality during high frequency mechanical ventilation

J. Veldman 1 , Z. van Kesteren 1 , M. Parkes 1 , M. Stevens 2 , J. van Schuppen 3 , J. van den Aardweg 4 , G. van Tienhoven 1 , A. Bel 1 , I. van Dijk 1 1 Amsterdam UMC - location University of Amsterdam, Department of Radiation Oncology, Amsterdam, The Netherlands; 2 Amsterdam UMC - location University of Amsterdam, Department of Anaesthesiology, Amsterdam, The Netherlands; 3 Amsterdam UMC - location University of Amsterdam, Department of Radiology, Amsterdam, The Netherlands; 4 Amsterdam UMC - location University of Amsterdam, Department of Pulmonology, Amsterdam, The Netherlands Purpose or Objective Respiratory motion management (RMM) in radiotherapy is recommended for tumours that move more than 5 mm due to breathing. During free breathing, large PTVs or ITVs are defined to account for respiratory motion, leading to unnecessary dose to healthy tissue. Reducing motion amplitude using mechanical ventilation may lead to reduction in target volumes. In our study, we quantify the effect of several breathing control strategies on organ and diaphragm motion, mainly measured on MRI. However, MRI is expensive and may be cumbersome for subjects. Alternatively, ultrasound (US) is more available and has a higher temporal resolution but may be more variable due to intra-operator variation. Our purpose was to determine if US is as accurate as MRI to quantify diaphragm motion during non-invasive mechanical ventilation at 60 breaths per minute (brpm). Materials and Methods After ethics committee approval and written informed consent, six healthy volunteers enrolled and practiced being non invasively ventilated at 60 brpm. In one subsequent session, diaphragm motion amplitude (A) was measured twice for 40 seconds using US cine-imaging (A1-US1 and A2-US1). We selected a sagittal plane on the mid-clavicular line and determined diaphragm motion amplitude on a point 10 cm from the imaging probe with a temporal resolution of 23 Hz. In two MRI sessions, on separate days, diaphragm motion amplitude was measured twice for 40 seconds (A1-MR1, A2-MR1, A1-MR2, A2 MR2) using a 1D navigator acquisition at 8 Hz, placed on the liver top at the level of the pancreas in anterior-posterior direction. From all 40 s measurements, we acquired diaphragm motion over time, to which we applied 5% outlier rejection (excluding 5% of the data points whilst minimizing the amplitude), resulting in an amplitude representative for the diaphragm motion amplitude imposed by the ventilation (Figure 1). We compared the first 40 seconds of each session (A1 US1, A1-MR1 and A1-MR2) and the second 40 seconds (A2-US1, A2-MR1 and A2-MR2) We used paired Wilcoxon’s test to test for significant differences (p<0.05). Additionally, we quantified the difference between A1-US1 and A2-US1, to identify any intra-operator variation.