ESTRO 2025 - Abstract Book

S114

Invited Speaker

ESTRO 2025

In order to allow for more rigorous probabilistic target definition and a probabilistic approach to treatment planning that could provide answers to these challenges, a new ICRU report on probabilistic treatment planning has been commissioned.

The report aims to:

• Enable probabilistic description of Clinical Target and Organs at Risk, replacing current volume-based binary descriptions • Support the migration to probabilistic uncertainties from the current construct of margin-based uncertainties • Support explicit definition of uncertainties , instead of current implicit inclusion of uncertainties • Facilitate integration of individual-based uncertainties , supplementing the population-based uncertainties • Enable comprehensive combination of uncertainties , instead of current ad-hoc combination of uncertainties • Provide optimal uncertainty management through robust optimization approaches These requirements lead to replacing the binary GTV and CTV concept by a probabilistic cartographic principle to create spatial probability distribution functions of Gross Tumor Maps (GTM) and Clinical Target Maps (CTM) . Similarly, the binary OAR concept is replaced with a probabilistic Organs at Risk Maps (ORM) probability distribution functions. The probabilistic GTM/CTM and ORM definitions require careful preparation, based on the patient-specific information extracted from imaging and other sources. Finally, the optimal treatment plans are obtained by explicit acknowledgment and integration of all uncertainties by means of robust optimization approaches.

4837

Speaker Abstracts Dose integration of combined treatment of EBRT and brachytherapy Georgina Fröhlich Centre of Radiotherapy, National Institute of Oncology, Budapest, Hungary. Deparment of Biophysics, Eötvös Loránd University of Sciences, Budapest, Hungary

Abstract:

Dose integration of external beam radiotherapy (EBRT) and brachytherapy (BT) is a complex problem because of the differences between the EBRT and BT patient anatomy, structures, images, and plans. The aim of the two treatment modalities is also different. In the conventional dose estimation method, the dose distribution of the EBRT is assumed completely uniform in the target volume and organs at risk, which was true in the conformal treatment plans only. In the era of image-guided arc therapy, this is a worst-case scenario and overestimates the total doses of the target volume and the organs at risk (OARs). Other dose summation methods used in the clinical practice – such as physical dose addition, DVH summation, rigid image registration, etc. - do not take into account these differences between EBRT and BT and result in inappropriate total doses. For the manual dose summation, focusing on the dose-volume parameters correlated with the clinical outcome is necessary. Nevertheless, the situation of these key parameters is different in EBRT and BT plans. The manual solution is time-consuming but can be used as a reference for discovering more complex methods, such as deformable image registration (DIR).