S1814
Physics - Dose prediction/calculation, optimisation and applications for photon and electron planning
ESTRO 2026
total uncertainty from every variable group. Results: Uncertainties in tissue properties alone resulted in a 95% confidence interval (CI) of 2.1 °C for T90. Uncertainties in positioning alone resulted in a 95% CI of 1.2 °C for T90. When combined, the CI increased to 2.4 °C. Median T90 values remained similar to nominal plans across all patients, but large inter-patient variability was observed. An example of nominal and standard deviation temperature distributions can be seen in Figure 1.
and longer BOT, along with reduced gamma pass rates (97% vs 100% for AAA/AXB-Dw). In contrast, AXB-Dw closely matched AAA in delivery parameters and achieved full QA pass rates. Conclusion: AXB provides more accurate dose modeling in heterogeneous media than AAA. However, AXB-Dm introduces higher complexity and reduced QA performance. AXB-Dw preserves the accuracy advantages of AXB while maintaining clinical efficiency and verification consistency, supporting its adoption as the preferred reporting mode for routine VMAT planning in head-and-neck cancer. Keywords: Acuros XB, Head-and-neck cancer, VMAT, Comprehensive uncertainty analysis in head and neck hyperthermia treatment planning using polynomial chaos expansion Roel C Kwakernaak 1,2 , Massimiliano Zanoli 1 , Zoltán Perkó 2 , Margarethus M Paulides 3,1 , Sergio Curto 1 1 Department of Radiotherapy, Erasmus MC Cancer institute, Rotterdam, Netherlands. 2 Radiation Science and Technology, Delft University of Technology, Delft, Netherlands. 3 Electrical Engineering, Eindhoven University of Technology, Eindhoven, Netherlands Purpose/Objective: Hyperthermia is a potent clinically used adjuvant treatment that enhances the effects of radiotherapy and chemotherapy due to several biological effects [1]. However, uncertainties in patient positioning, tissue properties, and water bolus cooling can compromise treatment quality. This study quantifies the impact of these uncertainties on hyperthermia treatment planning for head and neck cancer using the HyperCollar3D applicator [2]. Material/Methods: Proffered Paper 1007 A retrospective analysis was performed on 16 patients treated at Erasmus MC. Patient-specific models were created from CT scans and simulated in Sim4Life®. Treatment plans were optimized for conformal heating and constrained to a maximum temperature of 44 °C in normal tissue. Uncertainty propagation was modeled using polynomial chaos expansion with 56 stochastic variables, including dielectric and (non- temperature dependent) thermal tissue properties (based on the IT’IS database [3]), patient positioning (modeled as a multivariate Gaussian distribution with a 95% confidence ellipsoid corresponding to 5 mm), and bolus convection coefficient. For each patient, 100,000 error scenarios were evaluated to assess the impact on the dose metric T90 (temperature achieved in 90% of the target volume) and perform Sobol sensitivity analysis to calculate the contribution to the
Sensitivity analysis for the entire population revealed that dielectric tissue properties accounted for the largest percentage of T90 variance (mean 47%, min- max 15% - 89%), followed by positioning errors (22%, 1% - 53%) and thermal tissue properties (15%, 2% - 35%), while the bolus convection coefficient had negligible impact (4%, 0% - 34%) except for superficial targets (Figure 2). Deep-seated tumors seem to be more affected by variations in patient position (27%, 2% - 53%) compared to superficial tumors (9%, 1-18%).
Conclusion: The impact of delivery uncertainties in hyperthermia treatment planning varies substantially across patient cohorts. Our study revealed that uncertainty in dielectric properties have an important impact on the variance of T90. These findings highlight the necessity of the implementation of improved patient position registration and in vivo tissue characterization techniques to enhance the precision and clinical efficacy of hyperthermia treatments. References: [1] Oei AL, et al. Molecular and biological rationale of hyperthermia as radio- and chemosensitizer. Adv Drug Deliv Rev. 2020;163-164:84–97. doi:10.1016/j.addr.2020.01.003 [2] Verduijn GM et al. Deep hyperthermia with the hypercollar system combined with irradiation for advanced head and neck
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