ESTRO 2025 - Abstract Book

S2904

Physics - Dose prediction, optimisation and applications of photon and electron planning

ESTRO 2025

data from numerous treatment plans, an analytical function was proposed to assist planning physicists and responsible physicians in evaluating radiotherapy plans.

Material/Methods: The study was based on planning data from 196 lesions with target volumes (TV) ranging from 0.4 to 4.3 cm³, treated at our institution between 2018 and 2023. Treatment planning was conducted using the True Beam STx system and Eclipse software. All lesions received a dose of 20 Gy, normalized to the 80% isodose line. Two techniques, VMAT and DCA, were selected based on lesion asymmetry. A decision-making algorithm considering lesion asymmetry guided the technique choice and has been submitted for publication. For lesions up to 2 cm³, DCA was used, while for larger lesions (over 2 cm³), the selection between DCA and VMAT depended on the asymmetry index (Q Asym ). V10Gy values were analyzed, revealing two distinct linear behaviors for lesions below and above 2 cm³. For lesions up to 2 cm³, a linear relationship of 3.1×TV+0.4 was observed (blue line), while larger lesions exhibited a linear relationship of 2.5×TV+1.6 (green line). An analytical function, V10Gy=3.56×TV 0.848 , describes the dependency of V10Gy on TV with an R² value of 0.995 across all lesions. Results: The proposed function represents the upper boundary of the 95% confidence interval for our data. The function V10Gy = 4×TV 0.8 is a simple analytical approach for predicting the maximum expected V10Gy for all examined lesions with 95% confidence. This function proved to be a useful tool for evaluating outliers and serves as an internal quality criterion at our institution. The presented diagram illustrates our observations, with the black line representing the analytical function across the entire data set and the red line indicating the upper 95% confidence interval boundary.

Figure: V10Gy vs TV Diagram The figure below illustrates the observed linear relationships (blue and green lines) and the analytical function fitting.

Conclusion: The developed analytical function offers a valuable tool for objective assessment of plan quality and identification of outliers. It has the potential to be used as a quality criterion and for standardized collaboration with other institutions. In cases of significant deviations, plans can be reviewed, and treatment techniques adjusted to further enhance treatment quality.

Keywords: V10Gy Prediction, Lesion Volume, Plan Quality