ESTRO 2024 - Abstract Book

S4702

Physics - Optimisation, algorithms and applications for ion beam treatment planning

ESTR0 2024

Results:

All plans respected clinical goals on p-CT for target coverage and OAR constraints. Considering plan recalculation on rv-CT2, variations to nominal plan on anorectal D1 were on average smaller for the rob_plans than for the clinical ones ((1.1±0.8)Gy(RBE) vs (1.9±0.9)Gy(RBE)). Nevertheless, when anorectal D1 constraint was not fulfilled for a clinical plan (4 out of 10 plans) the corresponding rob_plan was not satisfactory as well. Relative to the target volumes, D99, D95 and D1 variations to nominal plan were less than 1.4 Gy(RBE) for the two plan types indicating good robustness for both approaches. Differences between corresponding dose volume points for both OAR and target for the two groups of plans were not significant.

Conclusion:

Rob_plans provided similar results in terms of capability to mitigate unpredicted anatomical variations compared to clinical plans at the cost of longer (1.5-2x) computational time. In contrast to a similar approach for H&N [4], inadequate results on relevant OARs suggest that the plan-of-the-day approach might be more appropriate for the gynaecological district.

Figure 1. Targets (red-proton target, green-C-ion target) and anorectum contours on rv-CT1 (continuous) and rv CT2(dashed). Imaging data on rv-CT1 could hardly help the optimization algorithm to predict the rectum contours on rv-CT2.