ESTRO 2024 - Abstract Book

S3630

Physics - Dose prediction, optimisation and applications of photon and electron planning

ESTRO 2024

Results:

A novel method for creating 4D dose distributions to model panning/tilting DTT within the TPS was successfully developed. Ten OARs (one per dataset) would exceed their dose limit during a DTT treatment if the exhale-phase CT calculation was used for planning. After applying the two proposed planning strategies, the “Boolean OAR” method successfully spared 7/10 OARs, although planning target volume (PTV) coverage was reduced significantly (p=0.009). The “Aperture Sorting” method successfully spared 9/10 OARs and PTV coverage did not significantly change (p=0.377). Not all apertures needed sorting to reduce the OAR maximum dose below its constraint. The images in figure 1, step 3b depict a beam’s-eye-view of two apertures and their relative position to an OAR on both breathing phases (OAR in and OAR ex , overlaid on the same image for comparison). The left aperture was assigned to the exhale-phase. The right aperture had little effect on OAR dose and remained unassigned. The “Aperture Sorting” method would require a unique treatment delivery where apertures assigned to a certain respiratory phase are delivered during that phase only, and those unassigned are delivered with DTT regularly. The results from this study are summarized in figure 2. The maximum dose (D max ) to 0.03cc and the PTV coverage (V 100% ) for the ten datasets is tabulated for the (1) original exhale-phase plan, (2) original plan after a 4D dose calculation, (3) 4D calculations after applying the “Boolean OAR” strategy, and (4) 4D calculations after applying the “Aperture Sorting” strategy. Shaded cells indicate where maximum dose constraints were exceeded. The results from a Student’s paired t-test with a two-tailed distribution are included showing the significance of the difference in mean PTV coverage for each planning strategy compared to the original plan’s 4D dose calculation.