ESTRO 2021 Abstract Book

S887

ESTRO 2021

Conclusion Repeated SRT is feasible for treatment of local or distant recurrent BM, it can avoid or delay WBRT. It is possible to predict which patients will most benefit from subsequent SRT based on initial, SRT1 and SRT2 characteristics. PO-1066 Quality and efficiency of automated organ at risk delineation on MRI in the brain J. Crouzen 1 , J. Zindler 1 , R. Wiggenraad 1 , M. Mast 1 , S. Lemmouy 1 , C. Gadellaa-van Hooijdonk 1 , S. van Geen 1 , S. Hutschemaekers 2 , M. Kiderlen 1 , J. Roos 1 , S. de Vet 1 , N. van der Voort van Zyp 1 , A. Petoukhova 1 1 Haaglanden Medisch Centrum, Radiotherapy, The Hague, The Netherlands; 2 Holland Proton Therapy Center, Radiotherapy, Delft, The Netherlands Purpose or Objective With modern radiotherapy techniques, organs at risk (OARs) can be actively avoided during treatment planning. Therefore, accurate delineation of OARs contributes to avoidance of acute and long-term toxicity. Recently, a European consensus was published of OARs delineation in the brain. 1 Contouring of OARs is time- consuming and automated software tools are available in treatment planning systems (TPS). We developed an automated OAR atlas in our TPS and evaluated its clinical performance compared to manual delineation. Materials and Methods Anonymized cerebral MRI scans (0.9x0.9x0.9mm 3 ) from twenty patients undergoing radiotherapy in the brain were available. OARs were manually contoured in our TPS (RayStation®) according to the European Particle Therapy Network (EPTN) consensus. 1 These OARs were checked by a radiation oncologist. These MRI scans with delineated OARs were used to develop an automated atlas in RayStation. The automated atlas was applied to the same twenty patients. Two radiation oncologists independently determined whether or not adjustments were required for each OAR in the automated atlas and counted the MRI slices which required adjustments. Observer agreement was also determined. The difference in volume between the automated and manual contours was calculated for each OAR as a percentage. The radiation oncologists were asked for the time required to contour the 34 OARs manually and the time required to adjust the automated OARs for clinical use.