3-Dimensional target coverage assessment for MRI guided esophageal cancer radiotherapy

M. R. Boekhoff, I. L. Defize, A. S. Borggreve, N. Takahashi, A. L.H.M.W. van Lier, J. P. Ruurda, R. van Hillegersberg, J. J.W. Lagendijk, S. Mook, G. J. Meijer

Research output: Contribution to journalArticlepeer-review

10 Citations (Scopus)


Purpose: This study aimed to quantify the coverage probability for esophageal cancer radiotherapy as a function of a preset margin for online MR-guided and (CB)CT-guided radiotherapy. Methods: Thirty esophageal cancer patients underwent six T2-weighted MRI scans, 1 prior to treatment and 5 during neoadjuvant chemoradiotherapy at weekly intervals. Gross tumor volume (GTV) and clinical target volume (CTV) were delineated on each individual scan. Follow-up scans were rigidly aligned to the bony anatomy and to the clinical target volume itself, mimicking two online set-up correction strategies: a conventional CBCT-guided set-up and a MR-guided set-up, respectively. Geometric coverage probability of the propagated CTVs was assessed for both set-up strategies by expanding the reference CTV with an isotropic margin varying from 0 mm to 15 mm with an increment of 1 mm. Results: A margin of 10 mm could resolve the interfractional changes for 118 out of the 132 (89%) analyzed fractions when applying a bone-match registration, whereas the CTV was adequately covered in 123 (93%) fractions when the registration was directly performed at the CTV itself (soft-tissue registration). Closer analyses revealed that target coverage violation predominantly occurred for distal tumors near the junction and into the cardia. Conclusion: Online MR-guided soft-tissue registration protocols exhibited modest improvements of the geometric target coverage probability as compared to online CBCT-guided bone match protocols. Therefore, highly conformal target irradiation using online MR-guidance can only be achieved by implementing on-table adaptive workflows where new treatment plans are daily generated based on the anatomy of the day.

Original languageEnglish
Pages (from-to)1-7
Number of pages7
JournalRadiotherapy and Oncology
Publication statusPublished - 2020 Jun


  • Adaptive radiotherapy
  • Esophageal cancer
  • Interfractional motion
  • MR guided radiation therapy
  • Treatment margin


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