S2919
RTT- RTT operational practice and workflow innovations
ESTRO 2026
without reoptimization. Evaluation included: (1) geometric comparison of deformed CTVs on cCBCT to manual delineated CTVs on rCT using Dice (DSC), surface Dice (sDSC) and Hausdorff 95% (HD95) metrics; (2) dosimetric assessment and offline plan adaptation decision-making was based on combining the following criteria for both CTVprim and CTVelec: CTV V95% < 98%, Δ D98% > 3%, D2% > 107%, and PTV V95% < 95%. OARs (spinal cord, brainstem, salivary glands, oral cavity, pharyngeal constrictors) were assessed for Dmax and Dmean against institutional constraints. Results: For CTVprim the mean DSC (+1SD) was 0.82 (0.09), sDSC 0.80 (0.17) and HD95 5.8 mm (2.9 mm), and for CTVelec 0.82 (0.04), 0.84 (0.10) and 5.8 mm (2.2 mm), respectively, indicating that deformed CTV structures on CBCT are geometrically acceptable. Nine of fifteen patients did not meet the clinical goal for CTV V95% (range: CTVprim 81.4–100%, CTVelec 80.3–100%; Fig. 1), and seven of these also failed the Δ D98% criterion ( Δ D98% [+1SD]: − 5.0% [6.5%] and − 3.2% [3.9%], respectively). Five patients exceeded PTV constraints, while D2%, OAR Dmax, and Dmean aims were never violated. Agreement between workflows was observed in twelve of fifteen patients; in three cases, manual review identified adaptation needs not flagged by the semi-automatic approach (false negatives). Figure 2 illustrates anatomical and dosimetric differences between pCT and cCBCT.
frequency of re-imaging during CBCT evaluation. The clinical efficacy of this protocol will undergo evaluation in the immediate future. Overall, systematic auditing of re-imaging will provide an effective method for evaluating protocol performance and overall operational effectiveness. References: 1) Chee D, Buckley L. Application of repeat image analysis to radiation therapy imaging modalities as a quality improvement tool for image guided radiotherapy. J Appl Clin Med Phys. 2023 Sep;24(9):e14019. doi:10.1002/acm2.14019. Epub 2023 May 4. PMID: 37143316; PMCID: PMC10476973.2) Jadon R, et al. A systematic review of dose-volume predictors and constraints for late bowel toxicity following pelvic radiotherapy. Radiat Oncol.2019 Apr 3;14(1):57.doi:10.1186/s13014-01912628. PMID: 30943992; PMCID: PMC6448293.3) Webster A, et al. Image-Guided Radiotherapy for Pelvic Cancers: A Review of Current Evidence and Clinical Utilisation. Clin Oncol (R Coll Radiol).2020Dec;32(12):805816.doi:10.1016/j.clon.2020 .09.010. Epub2020Oct16. PMID: 33071029. Keywords: Quality improvement, Gynecology, Image- guided Semi-automated quantitative workflow for offline plan adaptation in head and neck radiotherapy C.C.H. Warmerdam, K.F. Crama, R. de Jong, M.A. de Jong, E.A. Onderwater, E. Astreinidou Radiotherapy, LUMC, Leiden, Netherlands Purpose/Objective: To evaluate the feasibility of a semi-automatic dosimetric workflow based on corrected CBCT (cCBCT) to support offline plan adaptation decision-making in head and neck cancer patients (HN), and to compare its performance with the standard qualitative contour- based clinical workflow. Material/Methods: Fifteen HN patients treated with VMAT and online CBCT between October 2021 and April 2025, who underwent offline plan adaptation during their 25–35 fraction treatment course, were analyzed. For each patient, the planning CT (pCT), repeat CT (rCT), and the CBCT just before rCT were imported in RayStation v2023B. A cCBCT was generated using deformable registration to the pCT. Clinical Target Volume (CTV) of the primary tumor (CTVprim) and the elective neck (CTVelec) and Organs At Risk (OARs) were deformed to cCBCT. The original plan was recalculated on cCBCT Digital Poster 2171
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