ESTRO 2024 - Abstract Book

S4044

Physics - Inter-fraction motion management and offline adaptive radiotherapy

ESTRO 2024

Conclusion:

Online patient QA based on daily CT and EPID 3D dose reconstruction is feasible in clinical practice. Establishing tolerance ranges for trigger indicators based on a probability model is clinically acceptable and statistically significant. Anatomical error analysis can identify organ deformation in fractions and guide ART for future treatments.

Keywords: adaptive radiotherapy, nasopharyngeal cancer, EPID

1578

Proffered Paper

Pareto-optimal margin recipe for robust treatment of cervical cancer with plan-of-the-day IMPT

Sander C Kuipers 1,2 , Jeremy Godart 1,2 , Eva M Negenman 1,2 , Anouk Corbeau 3 , Andras G Zolnay 1 , Stephanie M de Boer 3 , Remi A Nout 1 , Mischa S Hoogeman 1,2 1 Erasmus MC Cancer Institute, University Medical Center Rotterdam, Department of Radiotherapy, Rotterdam, Netherlands. 2 HollandPTC, Department of Physics & Informatics, Delft, Netherlands. 3 Leiden University Medical Center, Department of Radiation Oncology, Leiden, Netherlands

Purpose/Objective:

Proton therapy has been proposed as an alternative to photon therapy for the treatment of primary locally advanced cervical cancer (LACC) to mitigate the treatment-induced morbidities. The large anatomic variations in the pelvis, due to changes in bowel and bladder filling, present challenges in achieving adequate target coverage. Plan-of-the-day approaches offer solutions to handle such motion. In a previous study, we showed that 5 mm set-up robustness and 3% range robustness resulted in an adequate coverage for the elective lymph node clinical target volume (CTV-E). However, these settings were insufficient for achieving adequate target coverage for the low-risk CTV (CTV-LR), which includes the uterus, parametria and proximal vagina, due to its large inter and intrafraction motion. This study aims to determine an anisotropic margin combination that can complement the existing 5mm/3% robustness setting for CTV-LR in a plan-of-the-day setting. The goal for this margin combination is to ensure adequate target coverage while limiting the expansion of the internal target volume. To achieve this, we created Pareto fronts to find the optimal margin setting

Material/Methods:

In this study we analyzed thirteen patients treated for LACC. For each patient, both a full and empty-bladder planning CT scan (pCT) and three to five weekly repeated CT scans (reCTs) were available. One to four ITVs were constructed by interpolating between the CTV-LRs on the pCTs, depending on the range of motion of the uterus. A treatment plan was created for each ITV and bundled in a plan-library. Four-beam Pareto-optimal IMPT treatment plans were produced using our in-house automated treatment planning system. All plans followed the EMBRACE-II planning