Florit Marcuse1, Stephanie Peeters2, Kato Herman1, Femke Vaassen2, Wouter van Elmpt2, Alexander P. W. M. Maat3, John Praag4, Charlotte Billiet5, Paul Van Schil6, Maarten Lambrecht7, Dirk Van Raemdonck8, Kim Cao9, Madalina Grigoroiu10, Nicolas Girard11, Monique Hochstenbag1, Jos Maessen12, Dirk De Ruysscher2
1Department of Pulmonology, Maastricht University Medical Center+, Maastricht, The Netherlands;
2Department of Radiation Oncology (Maastro Clinic), GROW School for Oncology and Developmental Biology, Maastricht University Medical Center+, Maastricht, The Netherlands;
3Department of Cardiothoracic surgery, Erasmus Medical Center, Rotterdam, The Netherlands;
4Department of Radiation Oncology, Erasmus Medical Center, Rotterdam, The Netherlands;
5Department of Radiation Oncology, Antwerp University Medical Center, Antwerp, Belgium;
6Department of Thoracic and Vascular Surgery, Antwerp University Hospital and Antwerp University, Antwerp, Belgium;
7Department of Radiation Oncology, University Hospitals Leuven/KU Leuven, Leuven, Belgium;
8Department of Thoracic Surgery, University Hospitals Leuven/KU Leuven, Leuven, Belgium;
9Department of Radiation Oncology, L’Institut du Thorax Curie-Montsouris, Paris, France;
10Department of Thoracic surgery, L’Institut du Thorax Curie-Montsouris, Paris, France;
11Institut du Thorax Curie-Montsouris, Institut Curie, Paris, France and UVSQ, Paris Saclay, Versailles, France;
12Department of Cardiothoracic surgery, Maastricht University Medical Center+, Maastricht, The Netherlands
Correspondence to: Florit Marcuse. Department of Pulmonology, Maastricht University Medical Center+, Limburg, Maastricht, The Netherlands. Email: florit.marcuse@mumc.nl.
Background: The detailed definition of the clinical target volume (CTV) for post-operative radiotherapy (PORT) for thymoma is largely unexplored. The aim of this study was to analyse the difference in CTV delineation between radiation oncologists (RTO) and surgeons.
Methods: This retrospective multi-center study enrolled 31 patients who underwent PORT for a thymoma from five hospitals. Three CTVs were delineated per patient: one CTV by the RTO, one CTV by the surgeon (blinded to the results of the RTO) and a joint CTV after collaboration. Volumes (cm3), Hausdorff distances (HD) and Dice similarity coefficients (DSC) were analyzed.
Results: RTO delineated significantly bigger CTV than surgeons (mean: 93.9±63.1, versus 57.9±61.3 cm3, P=0.003). Agreement was poor between RO and surgeons, with a low mean DSC (0.34±0.21) and high mean HD (4.5±2.2 cm). Collaborative delineation resulted in significantly smaller volumes compared to RTO (P<0.001). A mean volume of 18.9 cm3 (±38.1) was included in joint contours, but missed by RTO. Conversely, a mean volume of 55.7 cm3 (±39.9) was included in RTO’s delineations, but not in the joint delineations.
Conclusions: To the best of our knowledge, this is the first study investigating CTV definition in thymoma. We demonstrated a significant variability between RTO and surgeons. Joint delineation prompted revisions in smaller CTV as well as favouring the surgeons’ judgement, suggesting that surgeons provided relevant insight into other risk areas than RTO. We recommend a multidisciplinary approach to PORT for thymomas in clinical practice.
Keywords: Thymomas; post-operative radiotherapy (PORT); clinical target volume (CTV)
