ESTRO 2024 - Abstract Book

S3641

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

ESTRO 2024

3.5 Gy for rotating machine components (≤ 2°), and < 7.5 Gy for MLC-positioning uncertainties (≤ 1 mm) for both DTRT and VMAT.

For structures in the VMAT beam-plane, planning goals were more often respected for DTRT than for VMAT across all US. For example, DTRT fulfilled the oral cavity objective of mean dose < 40 Gy in 2618 out of the 3486 US, whereas VMAT fulfilled it in 2352 out of the 3486 US. Structures outside the VMAT beam-plane received significantly more dose with DTRT than VMAT (e.g., average mean dose to the eyes is 2.8 Gy higher for DTRT than VMAT, p < 0.01) with significant differences in robustness for all the investigated patient-setup and machine US. The dose remained well below the planning goals for all US for the optical structures and the brain. However, in some cases the uncertainties lead to breaching of the planning goals for DTRT for the hippocampus. In figure 1, an evaluation of robustness to patient-setup uncertainties for one example case is shown. The dosimetric benefits of DTRT for sparing OARs in the VMAT beam plane persisted even in the presence of uncertainties, at the cost of increased dose to OARs above the VMAT beam-plane.

DTRT plans had significantly lower NTCP values compared to VMAT plans. NTCP values for moderate to severe xerostomia and grade ≥ II dysphagia when no uncertainties were considered were on average/maximum 0.5/3.6 (p = 0.01) and 2.1/5.2 (p <0.01) percentage-points lower for DTRT than VMAT, respectively. DTRT maintained this statistically significant advantage across all investigated US except for MLC positioning uncertainties, where the observed difference did not reach statistical significance for xerostomia (figure 2).