ESTRO 2022 - Abstract Book

S822

Abstract book

ESTRO 2022

Conclusion No difference in whole breast volume was observed between the pts in the two arms of the DBCG PBI trial, but the irradiated breast volume was significantly smaller with PBI. The frequency of breast induration grade 2/3 at 3 yrs after RT increased significantly with increasing irradiated breast volume, thus strongly favouring small volumes and PBI.

OC-0931 Inter-center variations in contouring and planning compromises in the DBCG Skagen trial

E.L. Lorenzen 1 , M.S. Thomsen 2 , T. Bechmann 3 , M. Berg 4 , M.H. Nielsen 5 , H.V. Hansen 6 , K. Boye 6 , T. Lörincz 7 , I. Jensen 8 , S.A. Al-Rawi 9 , M.M.B. Nielsen 9 , L.W. Matthiessen 10 , K. Andersen 10 , M.R. Jensen 11 , J. Overgaard 12 , B.V. Offersen 12 1 Odense University Hospital, Laboratory of Radiation Physics, Odense, Denmark; 2 Aarhus University Hospital, Department of Medical Physics, Aarhus, Denmark; 3 Vejle Hospital, Department of Oncology, Vejle, Denmark; 4 Vejle Hospital, Department of Medical Physics, Vejle, Denmark; 5 Odense University Hospital, Department of Oncology, Odense, Denmark; 6 Rigshospitalet, Department of Oncology, Copenhagen, Denmark; 7 Aalborg University Hospital, Department of Oncology, Aalborg, Denmark; 8 Aalborg University Hospital, Department of Medical Physics, Aalborg, Denmark; 9 Zealand University Hospital, Department of Oncology and Palliative Care, Naestved, Denmark; 10 Herlev and Gentofte Hospital, Department of Oncology, Herlev, Denmark; 11 Rigshospitalet, Danish Breast Cancer Cooperative Group Secretariat, Copenhagen, Denmark; 12 Aarhus University Hospital, Department of Experimental Clinical Oncology, Aarhus, Denmark Purpose or Objective In the Danish Breast Cancer Group (DBCG) Skagen trial 1, 2963 high-risk breast cancer patients receiving loco-regional radiotherapy were randomized to 40 Gy in 15 fractions versus standard 50 Gy in 25 fractions. DICOM data were collected for all patients treated at the Danish centers between 2015 and 2021, allowing for investigation of inter-center variations in contouring practice and doses to organs at risk. While randomization was stratified according to center and systemic therapy thereby adjusting for potential inter-center variation, future analysis on other exposures could be affected by inter-center variations in radiotherapy practice between the centers. Materials and Methods 1937 treatment plans submitted from the seven participating Danish centers to the national DICOM collaboration system (DcmCollab) were available for analysis. Seven clinical target volumes (CTVs) (CTVp_Breast/CTVp_Chestwall, CTVn_IMN, CTVn_L1, CTVn_L2, CTVn_L3, CTVn_L4) and six organs at risk (OAR) (Heart, A_LADCoronary, Lung_ipsilat, Lung_contralat, Breast_contralat and HumeralHead) were delineated by all centers according to ESTRO guidelines. Full dose volume histograms were calculated for all contoured volumes. Results Volumes of CTVs and OARs stratified by center are shown in Figure 1. Good agreements were observed for all CTVs with only the CTVn_IMN showing relevant inter-center variation. For OAR the variation in lung delineations and contralateral breast between centers (data not shown) was low, whereas some variation was observed in both heart and humeral head delineations. Especially humeral head delineations varied in volume likely because several centers included more of the humeral bone than what should be included in the strict anatomical definition of the humeral head.