S1802
Physics - Dose prediction/calculation, optimisation and applications for photon and electron planning
ESTRO 2026
Digital Poster 410
Limitations related to target proximity and anatomical variations were identified and corrected through specific model adjustments. Conclusion: A structured, iterative optimization process enhances robustness and clinical feasibility of online ART for complex plans. This methodology provides a practical framework for extending adaptive workflows beyond simple cases, supporting broader clinical implementation of ART with maintained treatment quality and patient safety. Keywords: ETHOS, adaptive radiotherapy, plan optimization Digital Poster 383 Improving Treatment Without ART: Lessons from ETHOS to Enhance Non-Adaptive Practices Jarno Bouveret, vincent Fave, Amadine Halley radiooncology, Hôpital de la Tour, Meyrin / Genève, Switzerland Purpose/Objective: The systematic clinical implementation of online adaptive radiotherapy (ART) on the ETHOS system has allowed quantification of the dosimetric impact of daily anatomical variations. Insights from over 2,000 automated recalculations of the initial plan highlight key warning points directly applicable to non-adaptive radiotherapy. Material/Methods: Daily plan adaptation optimizes tumor coverage in response to anatomical variations, which are rarely quantified in standard practice. This work aims to evaluate automated plan recalculations within the ART workflow to define actionable vigilance criteria for conventional radiotherapy. Results: Each ETHOS session begins with an automatic recalculation of the initial plan on the daily CBCT, generating comparative dose metrics for target volumes and organs at risk. A retrospective analysis of a pelvic patient sample, mainly prostate cases, correlated dosimetric deviations with anatomical variations visible on the CBCT. Conclusion: Recalculations identified clinically relevant situations, with loss of tumor coverage or OAR overexposure corresponding to variations visible on the CBCT. These observations allowed the definition of specific vigilance points, usable directly during positioning imaging to guide adjustments or re-planning decisions. Keywords: ETHOS, adaptive radiotherapy, ART
Dosimetric and NTCP comparison of tomotherapy plans for loco-regional nasopharyngeal carcinoma (NPC) on temporal-mandibular joint (TMJ) sparing Ho Yee Yung Radiotherapy, Hong Kong Sanatorium & Hospital, Hong Kong, Hong Kong Purpose/Objective: This study aims to evaluate the dose sparing ability of the temporomandibular joint (TMJ) between TMJ- sparing and routine non-TMJ-sparing tomotherapy planning for nasopharyngeal carcinoma (NPC) radiotherapy (RT) treatment, and to estimate the risk of radiation-induced trismus using a tissue complication probability (NTCP) regression model. Additionally, it investigates the plan quality and doses to surrounding organs at risk (OARs) for these two A retrospective cohort of 39 NPC patients treated at Hong Kong Sanatorium & Hospital between January 2020 and January 2024 was selected. Tomotherapy plans were conducted using both non-sparing and TMJ-sparing approaches, which minimize the mean dose to the TMJ to less than 18 Gy. The prescription from the clinical oncologist of the selected cases chosen for this study was consistent with the guideline of the Chinese Society of Clinical Oncology (CSCO), while the other dosimetric parameters for critical structures were aligned with the clinical oncologist's prescribed dose constraints, which were basically same as, or even tighter than, those recommended in the RTOG 0615 and RTOG 0225 treating with Intensity Modulated Radiotherapy (IMRT). Conformity number, homogeneity index, and doses to critical structures and treatment time were analyzed for plan quality assessment. The possibility of trismus was quantified using the NTCP model, which accounted for patient age, baseline maximum inter-incisal opening, and TMJ mean dose. All the data collected were evaluated by paired T-tests or Wilcoxon signed-rank tests. Results: No statistically significant differences were observed in target conformity, homogeneity, and radiation delivery time between TMJ-sparing and non-sparing plans (p>0.05). Apart from TMJs, masseter and lateral pterygoid muscles, TMJ-sparing plans resulted in significantly reduced mean doses to ipsilateral parotid planning approaches. Material/Methods: and mandible, as well as D10% of temporal lobes (p<0.05). Other adjacent OARs, including brainstem, optic chiasm and optic nerves, achieved no statistical significance between the two approaches (p>0.05). Importantly, TMJ-sparing plans yielded a substantial reduction in radiation-induced trismus risk, with NTCP differences ranging from 8.64% to 31.39%.
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