ESTRO 2022 - Abstract Book

S413

Abstract book

ESTRO 2022

All 3 oncologists preferred to delineate the structures on the MDIod rec. Grading mean value and std of MDIod were 2.5 (between usable and very useful) +/- 0.65 pooled over all patients and structures. In contrast, the 40KeV grading mean and std was 1.3 (slightly usable) +/- 0.92. There was a significant difference between the usefulness of the two DECT rec (p<1e- 16). Conclusion DECT based delineation can be a useful alternative to support the delineation process for prostate patients undergoing RT planning who cannot participate or have access to MR imaging. MDIod reconstruction seems especially useful

Mini-Oral: 11: Intra-fraction motion management

MO-0467 Dosimetric impact of intrafraction upper abdominal tumor motion during MR-guided SBRT

G. Grimbergen 1 , H. Eijkelenkamp 1 , H. Heerkens 1 , B. Raaymakers 1 , M. Intven 1 , G. Meijer 1

1 University Medical Center Utrecht, Department of Radiation Oncology, Utrecht, The Netherlands

Purpose or Objective Abdominal compression greatly mitigates the intrafraction motion of abdominal tumors and their surroundings during MR- guided SBRT (MRgSBRT) delivery. Nevertheless, residual motion can be of concern. The purpose of this study was to quantitatively assess the dosimetric impact of this residual motion for both the target and abutting organs at risk as part of our QA protocol. Materials and Methods Twenty patients were included that underwent online adaptive MRgSBRT for upper abdominal malignancies in five fractions of 8 Gy on a 1.5 T MR-linac. Patients were wearing a custom fitted polyurethane corset during treatment delivery for abdominal compression. During the entire beam-on time, interleaved coronal and sagittal cine MRIs were acquired at 2.8 Hz, from which the GTV motion was extracted with deformable image registration. This motion timeline was synchronized to the linac log files to translate the individual beams at each point in time during treatment delivery, which were summed to obtain the delivered dose (see fig. 1). Key DVH parameters of the GTV and neighboring OARs (duodenum, bowel structures and stomach) were compared between the planned dose and the delivered dose.