ESTRO 2022 - Abstract Book

S188

Abstract book

ESTRO 2022

Existing quadratic, dual quadratic and constraint dual fourth order CK models were extended with an option for fitting explicit linear time dependency during model updates. For 7500 synthetic patients, simulations were performed to establish inaccuracies in predicted internal fiducial positions with and without the novel time dependency extension. In building and updating of the novel models, the time dependency was only applied in case of detected statistically significant baseline drifts. A respiratory track generator was used to create motion tracks for the synthetic patients. For each track, respiratory motion baseline, amplitude, period, shape and noise were randomly drawn from distributions found in literature. Additionally, phase shifts of 0, 0.1, 0.2, 0.3 and 0.4rad, and linear baseline drifts of 0, 0.25 and 0.5mm/min were added to respiratory motion tracks in CC direction. For each treatment simulation, the prediction error in CC was quantified by R95; for 95% of the radiation time, the distance between the predicted and real internal fiducial position is ≤ R95. Results For the three investigated non-linear models Fig. 1 shows R95 differences between tracking with and without time dependency for a range of phase shifts and baseline drifts. In contrast to the current non-linear CK models, inclusion of time dependency could to a large extent avoid increase of predicted errors caused by baseline drifts. E.g. for a 0 phase shift, mean R95 for the dual quadratic model with time dependency went up from 2.0mm for 0mm/min drift to only 2.3mm for 0.5mm/min drift, while for the conventional dual quadratic model the increase was much larger, from 2.0mm to 4.9mm (Fig. 1). For larger phase shifts, time-dependent models still did better than the original models, but differences were slightly smaller (Fig. 1).

Conclusion The proposed non-linear correlation models with explicit time dependency significantly enhanced the accuracy of internal fiducial position prediction in respiratory tracking, compared to currently implemented CyberKnife models, while keeping the number of acquired X-ray images fixed.

PD-0229 3D abdominal organ motion correlates strongly with the diaphragm during prolonged breath-holds

J. Veldman 1 , Z. van Kesteren 1 , E. Gunwhy 1 , M. Parkes 1 , M. Stevens 2 , J. van den Aardweg 3 , G. van Tienhoven 4 , A. Bel 5 , I. van Dijk 6 1 Amsterdam UMC - Location AMC, Department of Radiation Oncology, Amsterdam, The Netherlands; 2 Amsterdam UMC - Locations AMC and VUmc, Department of Anaesthesiology, Amsterdam, The Netherlands; 3 Amsterdam UMC, Department of Pulmonology, Amsterdam, The Netherlands; 4 Amsterdam UMC, Department of Radiation Oncology, Amsterdam, The Netherlands; 5 Amsterdam UMC, Department of Radiotherapy, Amsterdam, The Netherlands; 6 Amsterdam UMC - Location AMC, Department of Radiotherapy, Amsterdam, The Netherlands Purpose or Objective Respiratory motion management (RMM) is recommended for tumours subjected to excursions of more than 5 mm. Prolonged breath-holds (PBH) of >5 minutes can be achieved by mechanical ventilation induced hypocapnia after preoxygenation. During these prolonged breath-holds, the lungs gradually deflate causing the right diaphragm to drift cranially by approximately 3.0 mm/min. Here, we studied the correlation between the diaphragm drift and abdominal organ motion