ESTRO 2021 Abstract Book

S1591

ESTRO 2021

electron beam through the 0.5 cm collimation hole leads to dose increasing by less than 5% in its area for both electron energies. The latter is caused by electron scattering at the interface of two media. Wedge-shaped filter allows radiation field modification. The semicircle-shaped absorber provides total absorption for 6 MeV and 12 MeV electrons, and dose increasing on its edges is observed only for bolus geometry for both energies. Conclusion The study demonstrates the applicability of 3D printed samples in clinical electron beam modulation. The efficiency of beam modulation was compared for two geometries, simulating bolus and compensator application. This work is supported by the Russian Science Foundation, project No. 19-79-10014. PO-1867 Fully-automated target delineation QA and creation of VMAT/IMRT dose optimization structures L.H. Praestegaard 1 1 Aarhus University Hospital, Oncology, Aarhus, Denmark Purpose or Objective For advanced radiotherapy treatment techniques like IMRT and VMAT, the optimization of the dose distribution by the dose planning system is typically guided by a large number of optimization structures . Examples include PTVs, structures handling PTV/OAR overlap, and avoidance structures outside the PTV with the intend to increase dose conformality. An optimization structure is typically created by manipulating existing target and OAR structures, or by drawing the optimization structure manually. This is a manual, error-prone, and labor-intensive process that normally takes 10-60 minutes for each dose plan. Furthermore, an optimization structure error will often require replanning of the treatment plan and may compromise the treatment quality if not identified. Materials and Methods Structure Tool is an in-house-developed Eclipse scripting API that fully automates the creation of optimization structures using a graphical user interface. The application supports 12 structure manipulation types as for example margin, Boolean, crop, convex hull (see figure 1), ROI, and structure postprocessing (details are confidential due to commercial interests, but will be fully disclosed at the conference). The manipulation types match and, in some cases, surpass the functionality of manual structure generation using Eclipse. In addition, the application supports 7 structure check types that automatically evaluates all structures for errors, including approval status, target stray voxels, possible lack of a bolus, structures outside the body, evaluation of the overlap of two structures, and evaluation of the volume of a Boolean operation of structures. At present, the application is used for 41 treatment techniques and for more than 90 % of the curative patients in our clinic.

Results Structure Tool has reduced the required time to create dose optimization structures from typically 10-60 minutes to less than 1 minute. In addition, human errors during manual optimization structure generation have been completely eliminated. This both saves replanning resources and improves treatment quality in case of critical optimization structure errors otherwise not identified before treatment. Also, Structure Tool has detected numerous target delineation errors (e.g. stray voxels, missing bolus, and high dose targets extending inside a low dose targets) since its introduction in our clinic in March 2020, further improving treatment quality. Conclusion Structure Tool provides fully-automated target delineation QA and creation of optimization structures, thereby eliminating tedious routine work and improving treatment quality. PO-1868 First dosimetric assessment of proton minibeam arc radiation therapy R. Ortiz Catalan 1 , L. De Marzi 2 , Y. Prezado 1 1 Institut Curie, Centre de Recherche, Orsay, France; 2 Institut Curie, Centre de Protontherapy, Orsay, France Purpose or Objective Proton Minibeam Radiation Therapy (pMBRT) (Prezado et al, 2013) and Arc therapy (Ding et al, 2016) are two radiotherapeutic approaches that, individually, have shown an enhancement of the normal tissue sparing potential. In this work, dose distributions resulting from the combination of these two techniques are assessed and compared with a single- field pMBRT treatment plan, which has been proven beneficial in previous animal in vivo studies (Prezado et al, 2018).