ESTRO 2022 - Abstract Book

S475

Abstract book

ESTRO 2022

Conclusion Mean OAR dose and NTCP values resulting from VMAT and IMPT plans based on automated DLC are in agreement with VMAT and IMPT plans based on manually adjusted DLC (mean dose deviations within 0.07 Gy, NTCP within 1 pp). This suggests a limited effect of the manual adjustments made to automatically segmented DLC for VMAT and IMPT treatment of oropharyngeal cancer patients.

MO-0550 Pre-study QA reduces delineation errors and minimize dose to OAR in a central lung tumour SBRT trial

L. Hoffmann 1 , G.F. Persson 2 , L. Nygård 3 , T.B. Nielsen 4 , S. Borrisova 5 , F. Gaard-Petersen 5 , M. Josipovic 6 , A.A. Khalil 7 , R. Kjeldsen 8 , M.M. Knap 9 , C. Kristiansen 10 , D.S. Møller 9 , W. Ottosson 5 , H. Sand 11 , R. Thing 12 , M. Pøhl 13 , T. Schytte 14 1 Aarhus University Hospital, Dept of medical Physics, Aarhus N, Denmark; 2 Copenhagen University Hospital, Dept of Oncology, Herlev-Gentofte Hospital, , Copenhagen, Denmark; 3 Copenhagen University Hospital, Dept of Oncology, Rigshospitalet, Copenhagen, Denmark; 4 Odense University Hospital, Laboratory of Radiation Physics, Odense, Denmark; 5 Copenhagen University Hospital, Dept of Oncology, Herlev-Gentofte Hospital, Copenhagen, Denmark; 6 Copenhagen University Hospital, Dept of Oncology, Rigshospitalet, Copengaheg, Denmark; 7 Aarhus university Hospital, Aarhus, Dept. of Oncology, Aarhus, Denmark; 8 Aalborg University Hospital, Dept. of Oncology, Aalborg, Denmark; 9 Aarhus university Hospital, Dept. of Oncology, Aarhus N, Denmark; 10 University Hospital of Southern Denmark, 8. Dept of Oncology, Lillebaelt Hospital, Vejle, Denmark; 11 Aalborg University Hospital, Dept of Medical Physics, Aalborg, Denmark; 12 University Hospital of Southern Denmark, Dept of Oncology, Lillebaelt Hospital, Vejle, Denmark; 13 Copenhagen University Hospital, Dept of Oncology, Rigshospitalet, Copenhagen, Denmark; 14 Odense University Hospital, Odense, Dept of Oncology, Odense, Denmark Purpose or Objective Stereotactic Body RT (SBRT) of central lung tumours are associated with a high risk of serious toxicity. Our multicentre STRICT LUNG trial evaluates safety and efficacy of SBRT for central tumours treated inhomogeneously to 56Gy in 8 fractions. We prioritized organs at risk (OAR) constraints over target coverage, making the dose plans very sensible to OAR delineation variations. Therefore, the Quality Assurance (QA) programme focused on adherence to protocol in OAR delineation, the dosimetric effects of interobserver variation and priorities in dose planning. Materials and Methods The trial consensus and QA process consisted of two parts: Delineation of bronchial tree and mediastinal tissue; Dose planning . For the delineation (D) part , CT scans with GTV delineated were distributed to seven physicians. Delineations were performed in three rounds, each with one new case. D1: Delineation based on guidelines, followed by consensus meeting D2: Delineation followed by consensus meeting leading to creation of an atlas D3: Delineation Delineation variability was measured as mean (H mean ) and maximum (H max ) Haussdorff distance. To evaluate the dosimetric effect of OAR delineation variability for each case, seven simulated treatment plans, repeatedly using each of the OAR structure sets from the seven physicians, were made and compared. All plans were made by one physicist using the same planning parameters.