ESTRO 2023 - Abstract Book

S747

Monday 15 May 2023

ESTRO 2023

Results Three patients with pancreatic cancer and four patients with prostate cancer were included in this study and treated with MRgRT without adverse events. During MRgRT, the CIED was in an MRI-compatible mode which necessitated cardiac monitoring of the patient. Two institutions use a pulse oximeter for heart rhythm monitoring while one institution also acquired ECG. At baseline, and when imaging the pelvic area, ECG was largely undisturbed. In contrast, ECG signal was unusable for pancreas and lung imaging because the electrodes were closer to the isocentre. Heartrate readouts were 70 bpm, 65 bpm, 142 bpm, and undetermined, respectively. Field-mapping in presence of CIEDs showed that median absolute frequency differences between static and dynamic situations, directly related to geometric offsets, were all smaller than the absolute offsets, except when the CIED was closer than 8 cm to the target in which case signal voids would have prevented target visualization (Fig. 2). For the leads, none of the offsets outside the signal voids were clinically relevant.

Conclusion MRgRT treatment of CIED patients using a 1.5T MR-linac is feasible and was applied successfully in seven patients. Both pulse oximeter and ECG can be used to monitor patients with CIED during MRgRT, although imaging can distort the ECG signal substantially. Field-mapping procedures can be used in moving targets nearby leads and CIEDs for geometric accuracy assessment of MRI during MRgRT, paving the way for treatment of thoracic cancer patients with a CIED.

PD-0901 Methodology to monitor changes in ECG in patients with lung cancer after radiotherapy C. Cunniffe 1 , A. McWilliam 1 , H. Zhang 2 , K. Banfill 3 , C. Faivre-Finn 1