ESTRO 2023 - Abstract Book

S582

Monday 15 May 2023

ESTRO 2023

9 SWOARS were reviewed on 85 cases-765 contours in total. Variation in delineation was observed in all submitted SWOARS (Fig 1), with the Larynx_G having the most unacceptable variations (60%), mainly due to arytenoids being excluded or air not edited out. Large variations were also seen in the Oral_Cavity (49%), Oeso_Inlet (46%) and Larynx_SG (41%) mostly due to incorrect lateral border at the mandible, incorrect inferior border of the cricoid, and air not edited out respectively. Overall, 32% contours had unacceptable variations. The predicted NTCPD6 differences between GS and SC ranged from 3.4 to -6.2%. Larger differences were seen in those cases with unacceptable variations in Larynx_SG or PCM_Superior (Fig 2).

Conclusion Protocol compliance to the PATHOS contouring atlas showed unacceptable variations in SWOAR delineation in 32% cases. These variations are of no clinical significance within the trial as treatment plans are not optimised to SWOARs. Of note, larger differences were present in the predicted NTCPD6 between GS and SC when the contours of the relevant SWOARS did not conform to protocol. Accurate SWOAR delineation is therefore an essential step in NTCP calculation and an important consideration when using NTCP models e.g.in plan optimisation or patient selection for treatment techniques. (PATHOS trial no: A25317) MO-0713 Inter-expert observer variance of organs at risk according to the DAHANCA guidelines K. Jensen 1 , E. Lorentzen 2 , J.G. Eriksen 3 , J. Johansen 4 , N. Gyldenkerne 4 , R. Zukauskaite 4 , M. Kjellgren 5 , E. Andersen 6 , C. Maare 6 , C.K. Lønkvist 6 , K. Nowicka-Matus 7 , W. Szejniuk 7 , M. Farhadi 8 , Z. Ujmajuridze 8 , K. Marienhagen 9 , T.S. Johansen 10 , B.S. Kristensen 10 , J. Friborg 10 , J. Overgaard 3 , C.R. Hansen 2 1 Aarhus University Hospital, Danish Center for Particle Therapy, Aarhus, Denmark; 2 Odense University Hospital, Laboratory of Radiation Physics, Odense, Denmark; 3 Aarhus University Hospital, Department of Experimental Clinical Oncology, Aarhus, Denmark; 4 Odense University Hospital, Department of Oncology, Odense, Denmark; 5 Aarhus University Hospital, Department of Oncology, Aarhus, Denmark; 6 Copenhagen University Hospital Herlev, Department of Oncology, Herlev, Denmark; 7 Aalborg University Hospital, Department of Oncology, Aalborg, Denmark; 8 Zealand University Hospital, Department of Oncology, Næstved, Denmark; 9 Universitetssykehus Nord-Norge, Department of Radiotherapy, Tromsø, Norway; 10 Rigshospitalet, Department of Oncology, Copenhagen, Denmark Purpose or Objective Organ at risk contouring is an important but time-consuming radiotherapy process that has become increasingly automated in recent years through computers and artificial intelligence. This has led to the development of automated contouring