Contouring variation affects estimates of normal tissue complication probability for breast fibrosis after radiotherapy

Tanwiwat Jaikuna, Eliana Vasquez Osorio, David Azria, Jenny Chang-Claude, Maria Carmen De Santis, Sara Gutiérrez-Enríquez, Marcel van Herk, Peter Hoskin, Maarten Lambrecht, Zoe Lingard, Petra Seibold, Alejandro Seoane, Elena Sperk, R. Paul Symonds, Christopher J. Talbot, Tiziana Rancati, Tim Rattay, Victoria Reyes, Barry S. Rosenstein, Dirk de RuysscherAna Vega, Liv Veldeman, Adam Webb, Catharine M.L. West, Marianne C. Aznar*

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

Abstract

Background: Normal tissue complication probability (NTCP) models can be useful to estimate the risk of fibrosis after breast-conserving surgery (BCS) and radiotherapy (RT) to the breast. However, they are subject to uncertainties. We present the impact of contouring variation on the prediction of fibrosis. Materials and methods: 280 breast cancer patients treated BCS-RT were included. Nine Clinical Target Volume (CTV) contours were created for each patient: i) CTV_crop (reference), cropped 5 mm from the skin and ii) CTV_skin, uncropped and including the skin, iii) segmenting the 95% isodose (Iso95%) and iv) 3 different auto-contouring atlases generating uncropped and cropped contours (Atlas_skin/Atlas_crop). To illustrate the impact of contour variation on NTCP estimates, we applied two equations predicting fibrosis grade = 2 at 5 years, based on Lyman-Kutcher-Burman (LKB) and Relative Seriality (RS) models, respectively, to each contour. Differences were evaluated using repeated-measures ANOVA. For completeness, the association between observed fibrosis events and NTCP estimates was also evaluated using logistic regression. Results: There were minimal differences between contours when the same contouring approach was followed (cropped and uncropped). CTV_skin and Atlas_skin contours had lower NTCP estimates (-3.92%, IQR 4.00, p < 0.05) compared to CTV_crop. No significant difference was observed for Atlas_crop and Iso95% contours compared to CTV_crop. For the whole cohort, NTCP estimates varied between 5.3% and 49.5% (LKB) or 2.2% and 49.6% (RS) depending on the choice of contours. NTCP estimates for individual patients varied by up to a factor of 4. Estimates from “skin” contours showed higher agreement with observed events. Conclusion: Contour variations can lead to significantly different NTCP estimates for breast fibrosis, highlighting the importance of standardising breast contours before developing and/or applying NTCP models.
Original languageEnglish
Article number103578
Number of pages9
JournalBreast
Volume72
Issue number1
DOIs
Publication statusPublished - 1 Dec 2023

Keywords

  • Breast cancer
  • Fibrosis
  • Inter-observer variation
  • Late effects
  • NTCP modelling
  • Radiotherapy

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