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Updated: Feb 12, 2026

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Does setup on rectal wall improve rectal cancer boost radiotherapy?

Jean-Paul J E Kleijnen1, Bram van Asselen2, Martijn Intven2

  • 1Department of Radiotherapy, University Medical Center Utrecht, Heidelberglaan 100, 3584 CX, Utrecht, The Netherlands. J.J.E.Kleijnen@umcutrecht.nl.

Radiation Oncology (London, England)
|April 5, 2018
PubMed
Summary

Setting up rectal cancer radiotherapy using the rectal wall as a surrogate for tumor position slightly reduces setup errors but does not decrease planning target volume margins. Direct tumor visualization is needed for improved accuracy.

Keywords:
BoostDose escalationGTVMRIMobilityPosition surrogateRectal cancerRectal wallSetupTumor

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Area of Science:

  • Radiation Oncology
  • Medical Imaging
  • Gastrointestinal Oncology

Background:

  • Pathological complete response (pCR) in rectal cancer patients after neoadjuvant chemoradiotherapy improves prognosis.
  • Escalating radiation dose increases pCR rates but requires large margins due to lack of tumor contrast on online imaging.
  • Accurate tumor setup is crucial for effective rectal cancer boost radiotherapy.

Purpose of the Study:

  • To evaluate the feasibility of using the rectal wall as a surrogate for tumor position in rectal cancer boost radiotherapy.
  • To assess setup errors when using rectal wall versus bony anatomy for patient setup.
  • To determine the correlation between rectal wall and tumor displacement during radiotherapy.

Main Methods:

  • Daily MRI scans were performed for 16 patients during one week of radiotherapy.
  • Tumor and rectal wall were delineated on MRI scans to determine displacements.
  • Setup errors were compared between bony anatomy and rectal wall surrogates, and rectal wall-tumor displacement correlation was analyzed.

Main Results:

  • Mean setup error was slightly lower when using the rectal wall (2.2 mm) compared to bony anatomy (2.7 mm).
  • Similar planning target volume (PTV) margins (8.0 mm) were required for both setup methods.
  • A moderate correlation (ρ = 0.66) was found between rectal wall and tumor displacement, with limitations in detecting motion along the rectal wall.

Conclusions:

  • Setup on the rectal wall offers a minor reduction in mean setup errors but necessitates comparable PTV margins to setup on bony anatomy.
  • While rectal and tumor mobility may be similar, current online imaging lacks anatomical landmarks to detect rectal wall displacements accurately.
  • Direct or indirect online tumor visualization is essential to reduce uncertainties in rectal cancer radiotherapy positioning.