ESTRO 2023 - Abstract Book

S728

Monday 15 May 2023

ESTRO 2023

in terms of DVH metrics was performed after manual import of each fraction into Eclipse treatment planning system (version 15.6). Subsequent analysis was done in Origin (v. 9.6). Results The overall duration of the oART workflow from the start of CBCT acquisition to the end of treatment was 32.9 min (SD = 6.3 min). Figure 1 shows a case for the differences in dose distribution between the scheduled (Fig. 1a) and corresponding adapted plan (Fig. 1b). A clear benefit in target coverage was achieved by adaptation to the actual uterus position. Figure 1c shows the DVHs of the most relevant structures, which were created by averaging all scheduled (dashed lines) and the corresponding adapted plans (solid lines). Improvements in target coverage differed between patients, as seen in Fig. 2a. Applying the scheduled instead of the adapted plan would result in greatly reduced DVH metrics for PTV D95% and D98%. Except for one patient dose to the rectum was reduced by oART (Fig. 2b). By applying the adapted plan the average reduction of mean rectum dose was 5.8%. An overall dose reduction to the bladder was achieved for three patients (Fig. 2b), with a negligible change in mean bladder dose of <0.1%. This conflicting picture for bladder sparing may be a consequence of prioritizing target volume coverage over OAR sparing and secondly of differences in bladder filling. Conclusion Initial clinical evidence shows that CBCT-based oART can provide significant dosimetric benefits in cervical cancer. This may translate in meaningful improvement in local control and OAR sparing.