ESTRO 2024 - Abstract Book

S4055

Physics - Inter-fraction motion management and offline adaptive radiotherapy

ESTRO 2024

In addition to the 10 clinical observed cases, we also simulated an additional 100 motion patterns per patient using the systematic, random and intrafraction motion patterns observed in all MR- Linac prostate cancer treatments at our institution. From these simulations we picked the motion pattern associated with the 10th percentile of lowest CTV covering to evaluate the dose-adaptive approach on challenging motion patterns, we refer to them as the worst case motions. We compared the accumulated dose of the dose-adaptive strategy, for actual and worst-case motions, to conventional OART plans with 3mm PTV margins. We investigated CTV (D98%, D2) and rectum, bladder (D2%) and CTV+10mm (D50%) and tested whether the observed differences were significant at p<0.05 using paired t-tests.

Results:

In Figure 1 boxplots for accumulated dose parameters are shown. Accumulated dose coverage CTV(D98) of the dose adaptive plans is above 33.25Gy for 8/10 and 9/10 for the actual and worst-case motions, with a median of 35.1 Gy and 34.9 Gy. It was around 0.5 Gy lower than the conventional plans, reflecting a difference in CTV(D98) in planned dose due to the plan normalization. A significant reduction in the accumulated rectum (D2), bladder(D2) and CTV+10mm(D50) parameters of around -3Gy was obtained. The median required inhomogeneities in the last fraction plans CTV+3mm(D2) increased to 8.4Gy and 9.2 Gy for the actual and worst-case motions respectively. Median accumulated CTV(D2) over the whole treatment does not change for the actual motions but increases significantly with median +0.7Gy for the worst-case motion patterns.