ESTRO 2024 - Abstract Book

S4092

Physics - Inter-fraction motion management and offline adaptive radiotherapy

ESTRO 2024

the plan actually selected during the treatment (“Manual-ART”); (iii) the plan providing the highest D95% to the daily CTV (“D95-ART”). These strategies were compared in terms of D95% to the CTV, Dmean and Dmax to the bladder and rectum. Each fraction was normalized according to the prescription value (45 Gy). The Wilcoxon signed rank test with Bonferroni correction was used to compare the three approaches.

Results:

Out of the 1217 automatically segmented CTVs, 930 were estimated as good or intermediate, and 287 as poor by the physician. Dosimetric results were performed only on good and intermediate segmentations.

The selection of PoD was consistent between D95-ART and Manual-ART plans for 56% of the fractions.

The D95% to CTV was significantly higher with D95-ART than with the manual-ART and no-ART (median values of 44.14 Gy, 43.92 Gy and 43.57 Gy, respectively (Fig 1)).

For the bladder and rectum, the differences were small, although significant in some cases. The differences were lower than a 1% increase for the two ART strategies, when compared to no-ART.

Conclusion:

PoD CBCT-based ART resulted to an increase of the dose delivered to the CTV. The selection of the daily PoD based on dosimetric coverage of the daily CTV significantly improved the D95% of CTV compared to a selection performed on CTV projection on daily CBCT. However, it did not result to a decrease of the dose to rectum and bladder. A reduction in PTV margins or an online adaptive strategy may help to spare organs at risk.

Keywords: cervix, plan-of-the-day, CBCT