Rectal motion in patients receiving preoperative radiotherapy for carcinoma of the rectum

Int J Radiat Oncol Biol Phys. 2011 May 1;80(1):97-102. doi: 10.1016/j.ijrobp.2010.01.042.

Abstract

Purpose: To assess the movement of rectum, mesorectum, and rectal primary during a course of preoperative chemoradiotherapy.

Methods and materials: Seventeen patients with Stage II or III rectal cancer had a planning CT scan with rectal contrast before commencement of preoperative chemoradiation. The scan was repeated during Weeks 1, 3, and 5 of chemoradiation. The rectal primary (gross tumor volume), rectum, mesorectum, and bladder were contoured on all four scans. An in-house biomechanical model-based deformable image registration technique, Morfeus, was used to measure the three-dimensional spatial change in these structures after bony alignment. The required planning target volume margin for this spatial change, after bone alignment, was also calculated.

Results: Rectal contrast was found to introduce a systematic error in the position of all organs compared with the noncontrast state. The largest change in structures during radiotherapy was in the anterior and posterior directions for the mesorectum and rectum and in the superior and inferior directions for the gross tumor volume. The planning target volume margins required for internal movement for the mesorectum based on the three scans acquired during treatment are 4 mm right, 5 mm left, 7 mm anterior, and 6 mm posterior. For the rectum, values were 8 mm right, 8 mm left, 8 mm anterior, and 9 mm posterior. The greatest movement of the rectum occurred in the upper third.

Conclusions: Contrast is no longer used in CT simulation. Assuming bony alignment, a nonuniform margin of 8 mm anteriorly, 9 mm posteriorly, and 8 mm left and right is recommended.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antimetabolites, Antineoplastic / therapeutic use
  • Combined Modality Therapy / methods
  • Contrast Media
  • Fluorouracil / therapeutic use
  • Humans
  • Movement*
  • Patient Positioning
  • Pelvic Bones / diagnostic imaging
  • Preoperative Care
  • Radiography
  • Radiotherapy Dosage
  • Radiotherapy Planning, Computer-Assisted / methods*
  • Rectal Neoplasms / diagnostic imaging*
  • Rectal Neoplasms / drug therapy
  • Rectal Neoplasms / pathology
  • Rectal Neoplasms / radiotherapy
  • Rectal Neoplasms / surgery
  • Rectum / diagnostic imaging*
  • Tumor Burden
  • Urinary Bladder / diagnostic imaging

Substances

  • Antimetabolites, Antineoplastic
  • Contrast Media
  • Fluorouracil