S1808
Physics - Dose prediction/calculation, optimisation and applications for photon and electron planning
ESTRO 2026
Purpose/Objective: To evaluate the performance and clinical applicability of an externally developed knowledge-based planning (KBP) model (RapidPlan, Eclipse) for prostate-only (excluding seminal vesicles) radiotherapy, through a dosimetric comparison between clinically approved plans and model-generated plans. Material/Methods: Twenty patients previously treated with prostate-only radiotherapy using volumetric modulated arc therapy were retrospectively included in this study. The prescription dose was 60 Gy to the planning target volume (PTV), delivered in 20 fractions. A RapidPlan model developed by another institution was applied to each patient using the same CT dataset, structures, and prescription dose as in the original clinical plan. The model-generated plans were initially optimized without manual adjustment. However, since the model did not include optimization objectives for the clinical target volume (CTV), additional optimization objectives for the CTV were added for each case to ensure adequate target dose coverage according to the local requirements. Dosimetric parameters analyzed included PTV coverage (D98%) and organs-at-risk (OAR) doses (rectum: V30Gy, V57Gy and bladder: V30, V50 Gy). Statistical comparisons were performed using Wilcoxon signed-rank test (p<0.05). Results: Incorporating CTV-specific optimization objectives improved CTV dose coverage, conformity, and homogeneity compared to the model without adjustments (Figure 1). PTV dose coverage (D98%) was comparable between clinical and RapidPlan-generated plans (median 96.0% vs 96.1%, p = 0.575) (Figure 2a). For OARs, RapidPlan-generated plans resulted in statistically significant reductions in rectal doses: V30Gy (median 26.1% vs 16.6%, p < 0.001) and V57Gy (median 4.2% vs 3.8%, p < 0.001), which is clinically relevant for reducing late rectal toxicity. In contrast, bladder doses resulted in no statistically significant differences: V30Gy (median 24.7% vs 25.4%, p = 0.341) and V50Gy (median 10.7% vs 10.9%, p = 0.349) (Figure 2b).
Results:
In our analysis, lung dose parameters were lower with DIBH, although the differences did not reach statistical significance. No change was observed in cardiac dose, whereas the most pronounced and statistically significant reduction was seen in liver dose parameters. Regarding treatment delivery, DIBH resulted in an average increase of approximately two minutes per session (see Figure 1). Conclusion: Our results support previously published evidence that DIBH offers dosimetric advantages in right-sided breast-only radiotherapy. In particular, we observed a significant reduction in liver dose and a trend toward lower lung exposure, while the increase in treatment delivery time remained minimal (<2 minutes). Considering the low proportion of centers currently implementing DIBH for right-sided treatments, our findings emphasize the potential benefit of broader adoption beyond left-sided cases. References: 1 T. Koivumäki, Physica Medica, 2025 (https://doi.org/10.1016/j.ejmp.2025.105028)2 Li, Z, BMC Cancer, 2024 (https://doi.org/10.1186/s12885- 024-12992-2)3 Mader T, ctRO, 2024 (https://doi.org/10.1016/j.ctro.2024.100731)4 Haji G, ROJ, 2019 (https://doi.org/10.3857/roj.2019.00206)5 Pandeli, C, RO , 2019 (https://doi.org/10.1186/s13014- 019-1430-x) Keywords: DIBH, Right-sided Breast Digital Poster 734 Validation of an externally developed RapidPlan model for prostate-only radiotherapy - A dosimetric evaluation of 20 patients Raul Argota-Perez 1 , Erik Mattsson 2 , Susan B. N. Biancardo 1 , Henriette Lindberg 1 , Wiviann Ottosson 1 1 Department of Oncology, Herlev and Gentofte Hospital, University of Copenhagen, Copenhagen, Denmark. 2 Department of Medical Physics, County Hospital Ryhov, Jönköping, Sweden
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