ESTRO 2022

Session Item

Monday

May 09

16:45 - 17:45

Room D4

Breast

Chair: John Maduro, The Netherlands;

Co-Chair: Meriem Bohli, Tunisia

Session Code: 3470

Session Type: Proffered Papers

Track: Clinical

16:55 - 17:05

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

Ebbe Laugaard Lorenzen, Denmark

Presentation Number: OC-0931

Abstract

Abstract Title:

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

Authors:

Ebbe Laugaard Lorenzen¹, Mette Skovhus Thomsen², Troels Bechmann³, Martin Berg⁴, Mette Holck Nielsen⁵, Henrik Villibald Hansen⁶, Kristian Boye⁶, Tamás Lörincz⁷, Ingelise Jensen⁸, Sami Aziz-Jowad Al-Rawi⁹, Mette Marie Bruun Nielsen⁹, Louise Wichmann Matthiessen¹⁰, Karen Andersen¹⁰, Maj-Britt Raaby Jensen¹¹, Jens Overgaard¹², Birgitte Vrou Offersen¹²

¹Odense University Hospital, Laboratory of Radiation Physics, Odense, Denmark; ²Aarhus University Hospital, Department of Medical Physics, Aarhus, Denmark; ³Vejle Hospital, Department of Oncology, Vejle, Denmark; ⁴Vejle Hospital, Department of Medical Physics, Vejle, Denmark; ⁵Odense University Hospital, Department of Oncology, Odense, Denmark; ⁶Rigshospitalet, Department of Oncology, Copenhagen, Denmark; ⁷Aalborg University Hospital, Department of Oncology, Aalborg, Denmark; ⁸Aalborg University Hospital, Department of Medical Physics, Aalborg, Denmark; ⁹Zealand University Hospital, Department of Oncology and Palliative Care, Naestved, Denmark; ¹⁰Herlev and Gentofte Hospital, Department of Oncology, Herlev, Denmark; ¹¹Rigshospitalet, Danish Breast Cancer Cooperative Group Secretariat, Copenhagen, Denmark; ¹²Aarhus University Hospital, Department of Experimental Clinical Oncology, Aarhus, Denmark

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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.

Material 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.

Conclusion

Since introduction of CT-based treatment planning around 2005-8, DBCG guidelines for both contouring and dose constraints have been agreed upon, and they are continuously evaluated and modified at national meetings and workshops. As a result most volumes were contoured consistently among centers, but surprisingly, systematic differences were present in some volumes. This illustrates the need for further actions in harmonizing delineation practices for these volumes. Future studies investigating outcomes related to dose to volumes such as the CTVn_IMN, heart and humeral head should consider the variation in delineation practices.