ESTRO 2024 - Abstract Book

S4 ESTRO 2024 bladder and rectum filling, or biological response of tumor to treatment. The second component covers the uncertainties arising from combining doses with varying fractionation, including the limitations of conventional radiobiological models for dose accumulation. The unique difficulties encountered in reirradiation scenarios involving BT further underscore the necessity for robust summation methodologies Practical clinical solutions for addressing these challenges are presented, including direct addition of EQD2 doses between BT and EBRT, with a worst-case scenario assumption regarding hotspot doses. Furthermore, evidence supporting the use of organ D2cm 3 in gynecological cancer for establishing dose-effect relationships for morbidity endpoints is presented Case examples will illustrate dose accumulation between BT and EBRT using image registration that highlight the application of advanced techniques in clinical practice. Furthermore, novel alternative approaches and future outlooks in dose summation are discussed. These include dose accumulation on hollow organ walls utilizing dose surface maps and the potential of deep-learning approaches for deformable image registration and dose accumulation between EBRT and BT This presentation aims to provide a comprehensive understanding of the challenges associated with dose summation in combined EBRT and BT treatments for gynecological cancer. By exploring practical solutions and emerging methodologies, it seeks to facilitate advancements in treatment planning and optimization, ultimately improving patient outcomes. Invited Speaker

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Accumulation for treatment monitoring

Lena Nenoff

OncoRay – National Center for Radiation Research in Oncology, Faculty of Medicine and University Hospital Cal Gustav Carus, TUD Dresden University of Technology, Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany. Helmholtz-Zentrum Dresden-Rossendorf, OncoRay, Dresden, Germany

Abstract:

Dose accumulation can merge the doses calculated on different images at different time points within or between fractions or even between different treatments. To combine doses, the underlying anatomical images have to be registered and the registration result is used to map the doses. In some anatomical areas this can be done with rigid image registration, but in most areas this requires deformable image registration (DIR). The mapped doses can be added up on the reference image. While DIR has a major impact on the accumulated dose, other effects such as biological effects, equivalent dose (EQD) or biological effective dose (BED) calculation, energy conservation and interpolation are relevant secondary effects that contribute to the overall dose accumulation uncertainty. In clinical practice, dose accumulation is applied on different time scales to monitor the treatment progress in different treatment phases. Depending on the time difference the dose accumulation uncertainty varies. Additionally, the impact of the dose accumulation depends on its application (Figure 1). The fastest time scale is a simple 4D dose calculation for tumors affected by intrafraction breathing motion. The dose is calculated in different breathing phases, mapped to a reference phase, and added up. This can be used to evaluate interplay effects [1,2] or the impact of the starting phase [3]. The uncertainty of 4D accumulated doses is rarely quantified, but likely highest in the area of the dose gradient and sliding surfaces, such as lung-rib cage [4]. Between fractions, dose accumulation is used to add up the summed treatment dose. With widely available daily 3D images the daily delivered dose can be reconstructed. Differences between planned and delivered doses can be evaluated and plan adaptation can be indicated [5]. Inter-fraction dose accumulation can be challenging especially in the presence of large changes or during adaptive radiotherapy [6]. The uncertainty the DIR and therefore the