Pelvic lymph node motion during cone-beam computed tomography guided stereotactic radiotherapy

J. Janssen*, F. H.E. Staal, J. A. Langendijk, S. Both, C. L. Brouwer, S. Aluwini

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review


Background and purpose: Stereotactic body radiotherapy (SBRT) is increasingly applied for pelvic lymph node recurrence. Thus far, knowledge on pelvic lymph node motion during CBCT-guided SBRT is lacking and the applied margins vary between institutions. This study evaluated pelvic lymph node motion during CBCT-guided SBRT and assessed the currently applied PTV margins of 3 and 5 mm.

Material and methods: In total, 45 pelvic lymph node metastases were included. One observer delineated 45 GTVs on planning CT, 224 GTVs on pre-fraction and 216 on post-fraction CBCT. The GTV centroid coordinates were derived from all images for inter- and intrafraction motion analysis. Additionally, we assessed the influence of treatment time and lesion location on lesion motion. The expected coverage of a 3-mm and 5-mm PTV margin was assessed using the inclusiveness index for GTVs on pre- and post-fraction CBCT.

Results: Lymph node interfraction motion was limited to 5 mm in 96–97 % of fractions for all translational directions and intrafraction lesion motion was limited to 3 mm in 97–100 % of fractions. Para-rectal lesions (11 %) were associated with significantly larger inter- and intrafraction motion compared to other pelvic locations and treatment duration showed no correlation with lesion motion. The mean (sd) lesion inclusiveness index was 99 % (5 %) for the 5-mm PTV margin and 96 % (9 %) for the 3-mm margin.

Conclusion: Pelvic lymph node motion during CBCT-guided stereotactic radiotherapy was within the widely applied PTV margin of 5 mm, providing an opportunity to reduce this margin for pelvic lymph node SBRT.

Original languageEnglish
Article number100794
Number of pages6
JournalClinical and Translational Radiation Oncology
Publication statusPublished - Jul-2024


  • Lymph nodes
  • Margins
  • Oligometastasis
  • Stereotactic radiotherapy
  • Target motion


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